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Dietary Fats and Health: Dietary Recommendations in the Context of Scientific Evidence1

  1. Glen D. Lawrence*

+Author Affiliations

  1. Department of Chemistry and Biochemistry, Long Island University, Brooklyn, NY
  1. *To whom correspondence should be addressed. E-mail:[email protected].
 
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Abstract

Although early studies showed that saturated fat diets with very low levels of PUFAs increase serum cholesterol, whereas other studies showed high serum cholesterol increased the risk of coronary artery disease (CAD), the evidence of dietary saturated fats increasing CAD or causing premature death was weak. Over the years, data revealed that dietary saturated fatty acids (SFAs) are not associated with CAD and other adverse health effects or at worst are weakly associated in some analyses when other contributing factors may be overlooked. Several recent analyses indicate that SFAs, particularly in dairy products and coconut oil, can improve health. The evidence of ω6 polyunsaturated fatty acids (PUFAs) promoting inflammation and augmenting many diseases continues to grow, whereas ω3 PUFAs seem to counter these adverse effects. The replacement of saturated fats in the diet with carbohydrates, especially sugars, has resulted in increased obesity and its associated health complications. Well-established mechanisms have been proposed for the adverse health effects of some alternative or replacement nutrients, such as simple carbohydrates and PUFAs. The focus on dietary manipulation of serum cholesterol may be moot in view of numerous other factors that increase the risk of heart disease. The adverse health effects that have been associated with saturated fats in the past are most likely due to factors other than SFAs, which are discussed here. This review calls for a rational reevaluation of existing dietary recommendations that focus on minimizing dietary SFAs, for which mechanisms for adverse health effects are lacking.

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Introduction

Since the Framingham Heart Study reported that high serum cholesterol was a major risk factor for coronary heart disease (1), there has been an aggressive campaign in the medical community to decrease serum cholesterol. It has been a widely accepted belief that dietary saturated fats and dietary cholesterol cause an increase in serum total cholesterol, as well as LDL-cholesterol (LDL-C)2 and thereby increase the risk of heart disease if consumed (2). Over the years, it became clear that high levels of LDL circulating in the blood are susceptible to lipid peroxidation, which results in the oxidized LDL being scavenged by macrophages lining certain arteries, particularly around the heart, leading to atherosclerosis (3). Although this mechanism provides a role for high serum LDL-C causing atherosclerosis, evidence of the involvement of saturated fats is lacking, even though it is well established that a diet high in saturated fat increases serum cholesterol and a diet high in polyunsaturated oil decreases serum cholesterol (45). In fact, PUFAs are the components that are oxidized and generate antigenic substances that are recognized by immune cells for clearance of oxidized LDL in atherogenesis (68).

Numerous reports and reviews in recent years have begun to call the perceived pernicious effects of dietary saturated fatty acids (SFAs) into question. The purpose of this review is to summarize the scientific understanding as it relates to dietary fats in health and disease, particularly with regard to the innocuous nature of SFAs and the physiological effects that have implicated PUFAs in numerous disorders and diseases. The role of dietary fats in cardiovascular disease (CVD) and many other diseases is complex, yet there is a powerful inertia that has allowed the saturated fat doctrine to endure.

Dietary fatty acids and serum cholesterol

Dietary fat studies in the mid-20th century stressed the relationship of dietary SFAs and PUFAs to serum cholesterol levels with an aim toward decreasing the likelihood of the development of coronary artery disease (CAD) and premature death (45). Once lipoprotein fractions were separated in the blood, it became evident that LDL and VLDL were the carriers of cholesterol that were most closely associated with risk of heart disease (9). Later it was found that the ratio of total serum cholesterol to HDL-C was a better indicator of heart disease risk (10). By the 1990s, the mechanisms by which dietary fats and specific types of fatty acids were regulating serum cholesterol and lipoproteins were beginning to be revealed.

A family of proteins known as sterol regulatory element binding proteins (SREBPs) were discovered in the early 1990s. These proteins move to the nucleus in cholesterol-depleted cells to alter transcription of several genes involved in lipid metabolism (11). When intracellular cholesterol levels are low, SREBP-1 promotes expression of genes for synthesis of cholesterol and LDL receptors that remove cholesterol from the circulation. When intracellular cholesterol levels are high, SREBP-1 is not activated by protease cleavage, and the genes for cholesterol production and LDL receptors are downregulated. SREBP-1 also activates promoters for genes involved in fatty acid synthesis and lipid storage (12). PUFAs, particularly docosahexaenoic acid and others to a lesser extent, regulate expression of the SREBP genes (13,14). Consequently, when PUFAs are present, there is less expression of SREBPs and enzymes for cholesterol synthesis, and the serum cholesterol pool decreases.

There appears to be a number of proteins that bind PUFAs and are involved in regulating gene expression, including a family of G protein–coupled receptors (15), as well as peroxisome proliferator–activated receptors-α and -γ, retinoid X receptors, and various other nuclear receptors (16). The liver uses a variety of these receptors or sensors for PUFAs to regulate storage and utilization versus oxidation of PUFAs (17). In this way, PUFAs can stimulate fatty acid oxidation in the liver to minimize their potential for free radical oxidation in the body when their levels are high in the diet. One must keep in mind that this complex array for regulation of expression of a wide range of genes is also subject to an even more complex array of responses to dietary PUFAs and other dietary factors.

Single nucleotide polymorphisms in genes for many of the above factors, as well as in genes for several apolipoproteins, TNFs, glutathione peroxidases, and other proteins result in a wide range of individual responses to dietary constituents. The consequences of such genetic variation can be either little change or very large changes in serum lipids and lipoproteins in response to diet, depending on an individual’s genetic makeup (18). However, one should not lose sight of the fact that levels of many other proteins are being altered in the process, which can give rise to a wide array of physiological responses that influence susceptibility to many unhealthy conditions, such as CVD and cancer.

Short-chain SFAs, such as those in dairy fat and coconut oil, can also influence gene expression via interactions with various G protein–coupled receptors that are linked to several hormonal responses, including insulin and leptin, that regulate overall energy metabolism in the body (19). It is clear that there are numerous sensors that respond to dietary PUFAs and short- or medium-chain SFAs (20).

Genetic factors

Brown and Goldstein (21) received the Nobel Prize in Physiology or Medicine in 1985 for their work on genetic defects in LDL receptors of people with familial hypercholesterolemia (FH). They identified several mutations that produce nonfunctional LDL receptors, resulting in death from atherosclerosis and heart disease at an early age. Individuals with FH have serum LDL-C in excess of 300 mg/dL (or 8 mmol/L), although LDL-C may be as high as 650 mg/dL (17 mmol/L) in homozygous individuals. Goldstein and Brown (22) also identified several genes that code for other proteins involved in cholesterol transport and metabolism, such as apolipoprotein B-100 (apo B), which is a component of LDL that binds to LDL receptors. There are other proteins involved in LDL synthesis, transport, and clearance that can result in a genetic predisposition to increased serum LDL cholesterol and FH (2325).

In the early 1990s, it was discovered that men with CVD tended to have smaller HDL particles than healthy controls (26). It was later found that LDL particle size was also significantly smaller in men with CAD than in case-matched controls (27), although another study showed the ratio of total serum cholesterol to HDL-C was a better predictor of CAD risk than LDL particle size (28). A prospective, population-based cohort study also found an increased risk of CAD in middle-aged men with smaller, dense LDL particles than in men with larger LDL particles, although the relationship did not show a linear dependence on particle size (29). It later became evident that LDL particle size was influenced by several factors and was not necessarily a useful predictor of heart disease risk; the nature of LDL is influenced by both dietary and genetic factors (30).

Lipoprotein (a) [Lp(a)] is a complex lipoprotein that has several properties in common with LDL. Like LDL and VLDL, Lp(a) contains apo B, but also contains highly variable forms of apolipoprotein(a) that strongly influence its atherogenicity and propensity to promote heart disease (31). The wide array of apolipoprotein(a) isoforms present in the human population may have caused some confusion regarding the role of Lp(a) in atherogenesis and CVD. The association of apo B with oxidized phospholipids was found to be dependent on Lp(a) (32). The presence of oxidized phospholipids and Lp(a) tend to be proinflammatory and promote atherogenesis.

Small, dense LDL particles rarely occur as an isolated condition, but are often associated with a specific phenotype that is characterized by hypertriglyceridemia, low HDL-C, abdominal obesity, insulin resistance, and other metabolic irregularities that lead to endothelial dysfunction and susceptibility to thrombosis (33). Small, dense LDL is also more susceptible to lipid peroxidation due to changes in the lipid composition, making it more atherogenic (34). LDL particles from the atherogenic phenotype contain less cholesterol and phospholipid, but more triglyceride. This phenotype is generally referred to as phenotype B and is characterized by elevated levels of apo B, which is found in LDL and VLDL (35).

There have been a host of proteins linked to lipoprotein metabolism and transport and a wide range of genetic variations identified that result in alterations of those proteins. Many are associated with HDL and larger HDL particle size, which is consistently associated with a decreased risk of CAD (36). HDL is important in reverse-cholesterol transport, bringing cholesterol from arterial deposits to the liver for processing, where it is converted to useful metabolites and eventually cleared from the body via bile secretions. A family of lipoprotein lipases, including hepatic lipase and endothelial lipase, are intimately involved in HDL metabolism. Endothelial lipase is upregulated during inflammation, a condition that increases LDL oxidation and atherogenesis (37). Genetic variation in apolipoprotein A-I, a major protein component of HDL, can result in larger but less stable HDL particles and decreased levels of circulating HDL (38). Cholesteryl ester transfer protein is generally considered to be protective, although this protein may transfer lipids from HDL to other lipoproteins that result in a less desirable serum lipid profile (39). HDL is emerging as a fascinating lipoprotein with a complex array of functions that involve both protein and lipid components. HDL has been found to influence immune function, vascular inflammation, glucose metabolism, and platelet function as well as other physiological phenomena unrelated to CVD (40).

Paraoxonase 1 (PON1) is another protein associated with HDL that exhibits esterase and lactonase enzyme activity, including metabolism of toxic organophosphorus pesticides and oxidized lipids in oxidized LDL particles. The levels of PON1 activity varies tremendously among humans, which depends to a large degree on genetic variation. However, environmental factors, such as dietary antioxidant consumption, alcohol consumption, and certain drugs can also influence PON1 activity (41). Dietary olive oil can increase levels of serum PON1 in some individuals, which is genotype dependent (42), whereas MUFAs and PUFAs can inhibit PON1 enzymatic activity (43). SFAs (palmitic and myristic) had virtually no effect on PON1 enzymatic activity. A recent study found that HDL isolated from patients with CAD lacks endothelial anti-inflammatory properties, has lower PON1 enzyme activity, and does not promote endothelial nitric oxide production (44), all of which are most likely tied to genetic rather than dietary factors.

Fatty acids involved in atherogenesis and CVD

Linoleic acid makes LDL more susceptible to lipid peroxidation and subsequent deposition of the oxidized LDL in macrophages lining the arteries (45). Several lipid peroxidation products have been shown to trigger transformation of circulating monocytes to macrophages that line the arteries and ultimately become foam cells (4647). Lipid peroxidation products also signal cells in the arterial intima to encapsulate foam cells by surrounding them with extracellular matrix proteins and eventually calcify the matrix (48). It would stand to reason that a greater abundance of PUFAs, relative to SFAs and MUFAs, during conditions of oxidative stress would provoke atherogenesis. The fibrous cap that is formed over fatty deposits makes them inaccessible to apolipoproteins such as apolipoprotein A-I or E, which are components of HDL, the lipoprotein that removes cholesterol from these deposits (49). The protein cap is characteristic of advanced atherosclerotic plaque and erosion of this protective cap by extracellular metalloproteases can release collagen and collagen-like fragments that trigger blood platelets to initiate a blood clot, which results in myocardial infarction or stroke (3).

Because saturated fats are not susceptible to lipid peroxidation, they have not been found to be involved in these mechanisms. This begs the question of how dietary polyunsaturated oils seem to lower the risk of CAD, even though many studies have shown no such effect. One important consideration is that foods that are considered sources of predominantly saturated fats, such as meats, are often cooked at high temperatures, which can induce lipid peroxidation in the minor amounts of PUFAs present in those animal products (5052). Oxidative stress and lipid peroxidation products are known to promote heart disease, cancer, and several other chronic diseases (5354). High-temperature cooking can also oxidize carbohydrates, producing a range of toxic oxidation products that promote oxidative stress, type 2 diabetes, and CVD (55). The preparation and cooking methods used for foods that are traditionally classified as saturated fat foods may be producing substances from PUFAs and carbohydrates in those foods that are promoting disease.

Human food preferences tend to favor foods with both fats and sugar (56), which complicates any attempts to correlate saturated fats with disease. Sugars readily undergo oxidation, with fructose generally getting oxidized many times faster than glucose, whereas sucrose is relatively resistant to oxidation (57). The oxidation products of these monosaccharides include glyoxal, methylglyoxal, and formaldehyde. Methylglyoxal has been shown to promote endothelial dysfunction as well as hypercholesterolemia in rats (58). Methylglyoxal is also associated with increased atherosclerosis and hypertension in humans (59). Formaldehyde and methylglyoxal have been implicated in endothelial injury, oxidative stress, and angiopathy (60).

Many clinical studies show that there are fewer coronary events when polyunsaturated oils replace saturated fats in the diet (61). However, a recent meta-analysis found that interventions using mixed ω3 and ω6 PUFAs resulted in a significant (22%) decrease in CAD events compared with control diets with fewer PUFAs. However, interventions that used ω6 polyunsaturated oils with no ω3 PUFAs showed ∼16% more cardiovascular events compared with the control diets, although the increased number was not statistically significant (62). It would seem that even moderate amounts of ω3 PUFAs in the diet result in attenuation of inflammatory responses that are reflected in the significant reduction in coronary events observed with increasing dietary PUFAs. Of the common vegetable oils, soy oil contains ∼7% ω3 PUFAs and canola oil as much as 10% ω3 PUFAs, whereas corn, safflower, and sunflower oils generally contain <1% ω3 PUFAs (63). Another systematic review found insufficient evidence to support an association (positive or negative) between CAD and several dietary factors, including SFAs or PUFAs, α-linolenic acid, total fat, meat, eggs, and milk (64).

Lipid peroxidation and inflammation

Lipid peroxidation is invoked as a mechanism for numerous adverse health effects, such as aging, cancer, atherosclerosis, and tissue necrosis. The greater in vivo susceptibility of ω6 PUFAs relative to the ω3 PUFAs, has placed the spotlight on these fatty acids as contributing to or exacerbating many ailments (68). The metabolism of arachidonic acid to bioactive eicosanoids is responsible for many of the biological processes that lead to inflammation. Indeed, steroidal and nonsteroidal anti-inflammatory drugs suppress inflammation by blocking the release of arachidonic acid from membranes or its subsequent metabolism to eicosanoids.

Studies of inflammation in rats have found that dietary manipulation of relative amounts of ω6 PUFA precursors can have profound effects on the degree of inflammation. Predominantly SFAs in the diet result in far less inflammation than diets with either ω3 (69) or ω6 PUFAs (70). Several studies have shown that dietary supplementation with ω3 PUFAs can reduce inflammation and make patients less dependent on drug therapy to manage the pain and stiffness of arthritis (7173). Patients should be advised to minimize their intake of ω6 oils when attempting ω3 supplementation as a therapeutic approach to reduce the inflammation of arthritis and other inflammatory syndromes (74,75). Small amounts of ω3 supplements in a sea of dietary ω6 oils would have relatively little chance of changing the course of an inflammatory response. Because dietary saturated fats do not promote inflammation, it may be wiser to minimize ω6 PUFAs and consume more SFAs to reduce various types of inflammation; most sources of MUFAs contain significant amounts of PUFAs as well. There have been few scientific studies along these lines because of the misguided concern that saturated fats, even those from vegetable sources such as palm and coconut oil, would be detrimental to one’s health.

The efficacy of ω3 supplements for inflammatory syndromes other than rheumatoid arthritis are less persuasive, although study designs are questioned regarding whether patients are advised to reduce their ω6 fatty acid intake (76). Fish oil supplements improved pulmonary function in some asthmatics (responders) but not in others (nonresponders). A relatively high ratio (10:1) of dietary ω6 to ω3 PUFAs resulted in diminished respiratory function in methacholine-provoked asthmatics, whereas a lower ratio (2:1) produced significant improvement in >40% of the study participants (77). A study in Japan showed beneficial effects of ω3 supplements in asthmatic children in a controlled hospital ward environment (78). A comparison of dietary saturated fats with polyunsaturated oils was not found in the literature for asthma studies. Such an approach would be logical for this life-threatening condition, in view of the benign nature of saturated fats and the fact that carbohydrates, especially sugars, may actually be augmenting the incidence of asthma (79).

Are low-fat, low-saturated fat diets healthier?

Studies with laboratory animals have shown that high-fat diets promote chemically induced cancers (8081). A study of chemically induced mammary tumors in rats found that ω6 PUFAs promoted tumor proliferation, whereas saturated fats or ω3 PUFAs did not promote tumors as much or even suppressed tumors, depending on what one uses as a reference (8283). Although 1 review and meta-analysis found that linoleic acid, the predominant ω6 fatty acid in vegetable oils, is not a risk factor for breast, colorectal, and prostate cancers in humans (84), there is evidence to the contrary that high intake of ω6 relative to ω3 PUFAs increases cancer risks (8587). There are multiple processes by which ω6 fatty acids can promote carcinogenesis; production of bioactive eicosanoids from arachidonic acid is 1 mechanism (8889). Nonsteroidal anti-inflammatory drugs as well as cyclooxygenase-2 inhibitors can suppress tumors by inhibiting production of prostaglandins, particularly those of the ω6 variety (90). Lipid peroxides are also known to promote chemically induced tumors (91), and PUFAs are highly susceptible to lipid peroxidation.

Investigators often seem to have a particular bias against saturated fats. One report showed that red meat alone was not significantly associated with colorectal cancer, although there was some increase in colorectal cancers with higher red meat intake [HR = 1.17 for highest vs. lowest intakes (95% CI = 0.92–1.49, P-trend = 0.08)]. Processed meats were significantly associated [HR = 1.42 (95% CI = 1.09–1.86, P-trend = 0.02)]. The authors then combined the data for red meat and processed meat to give a significant association and concluded that red and processed meat are positively associated with colorectal cancer (92). When specific types of meat were analyzed, significant risk was associated with pork [HR = 1.18 (95% CI = 0.95–1.48, P-trend = 0.02)] and lamb [HR = 1.22 (95% CI = 0.96–1.55, P-trend = 0.03)], but not with beef/or veal [HR = 1.03 (95% CI = 0.86–1.24, P-trend= 0.76)]. It is interesting to note that in 1 study, beef had a much lower ratio of PUFAs to SFAs than pork, but nearly the same ratio of PUFAs to SFAs as sheep (93). The ratio of MUFAs to SFAs in beef also varies, as it does in most meats, with the ratio ranging from ∼0.8 to 1.8, depending on breed and feeding practices (94).

Nitrite used in the preservation of many processed meats is known to form a carcinogen with secondary amines under acidic conditions that would prevail in the stomach (95). Others have found no association of red meat and only a very weak association of processed meat with breast cancer (96) and prostate cancer (97). Most studies find no differences in cancer risk with different types of fat, but do find associations with high levels of fat in the diet (81).

A recent meta-analysis (98) reviewed 20 studies with >1 million subjects and found that red meat was not associated with CAD events [RR = 1.00 (95% CI = 0.81–1.23, P-trend = 0.36)]. In contrast, processed meats were associated with increased incidence of CAD [RR = 1.42 (95% CI = 1.07–1.89, P-trend = 0.04)]. This indicates that saturated fat per se is not increasing CAD events, but other factors are, such as preservatives used in processed meats or other dietary substances that are being consumed in conjunction with processed meats. It is important to keep in mind that meats generally contain as much MUFA as SFA. Others are beginning to challenge the saturated fat hypothesis with closer analyses of past studies (99103).

Campaigns were waged against tropical oils (palm and coconut oils) in the early 1980s because of their high levels of SFAs, even though palm oil contains about as much MUFAs acids as SFAs and has an ample amount of PUFAs to keep serum cholesterol low. In fact, 2 studies showed that the higher ratio of SFAs to MUFAs in palm oil (1.1:1) compared with olive oil (0.22:1) had no effect on serum lipids in healthy volunteers (104105). Palm oil and olive oil have similar amounts (∼10%) of PUFAs. SFAs in coconut oil increase serum HDL-C more than LDL-C to give a more favorable lipid profile relative to dietary carbohydrates (10). Claims that tropical oils with a high SFA content increase the risk of CAD lack clear scientific evidence to that effect. Indeed, countries with high intake of tropical oils have some of the lowest rates of heart disease in the world (106).

Many of the shorter chain fatty acids found in milk fat and coconut oil have beneficial health effects. The shorter chain SFA in milk (C4–C12) are not only metabolized rapidly for energy in infants, but have been found to have important antiviral, antimicrobial, antitumor, and immune response functions (107). Lauric acid, which is present in milk and the most abundant fatty acid in coconut oil, is effective in preventing tooth decay and plaque buildup (108). Diets rich in coconut oils have also been shown to lower other risk factors for CAD, such as tissue plasminogen activator antigen and Lp(a) (109). The medium-chain SFAs in coconut oil and butterfat (milk) increase total serum cholesterol, but their positive effects on HDL-C are protective in many ways. There is also evidence that proteins, fats, and calcium in milk are beneficial in lowering blood pressure, inflammation, and the risk of type 2 diabetes (110111). Indeed, these constituents of milk have clear beneficial effects against metabolic syndrome, which is a major factor in promoting heart disease, as well as premature death from a variety of causes (112).

There has been a spate of recent publications in the biomedical literature that question the negative perception that dairy fats are bad for health. One meta-analysis showed that participants in prospective studies with the highest consumption of dairy products had a lower RR for all-cause mortality as well as for CAD, stroke, and diabetes compared with the lowest intake of dairy products (113). Many of the studies included in the analysis started before low-fat milk was available on the market. Another review arrived at the same conclusion that consumption of dairy products is not associated with higher risk of CVD (100). Although prospective cohort studies often find a significant reduction in the incidence of CAD with a larger ratio of PUFAs to SFAs in the diet (114), there are often many other factors related to overall health that correlate with the unsaturated to SFA ratio, such as exercise, a healthier lifestyle, and more fiber and less sugar in the diet.

Less fat generally means more carbohydrate

It should not be surprising that substitution of carbohydrates (starches) for saturated fats in the diet has relatively little effect on serum lipids. Excess carbohydrates are converted to fats for efficient energy storage, and the human body synthesizes primarily SFAs from excess carbohydrates, although MUFAs are also formed. Consequently, from a physiological viewpoint, there is no reason to believe that replacing fat in the diet with carbohydrate at a constant caloric intake will improve the serum lipid profile significantly. Indeed, a low-fat, high-carbohydrate diet causes an increase in serum triglycerides and small, dense LDL particles (115), which are more strongly associated with CAD than serum total cholesterol or LDL-C. When dietary fat is replaced by carbohydrate without changing the fatty acid composition of the fat, there is no change in LDL-C or HDL-C, but there is an increase in serum triglycerides (116). However, if there is a higher percentage of PUFAs and lower SFAs in a low-fat diet, serum total cholesterol and LDL-C will decrease (117).

Young children who consumed more fruit juice than their peers were shorter in stature and had greater BMI than their peers who drank less fruit juice (118). A trend of increased fruit juice consumption by infants and children in recent years has coincided with a decrease in milk consumption (119). The rates of childhood obesity have skyrocketed since the introduction of low-fat milk, although high fructose corn syrup (HFCS) became omnipresent in foods at the same time and is more strongly associated with obesity than dietary fat (120121). As stated previously, the short-chain SFAs in milk provide valuable antibacterial and antiviral activities, which would result in healthier children. The short-chain SFAs found in milk act as signaling agents in the immune system (122). Infections in children also correlated with higher levels of atherogenic oxidized LDL, as well as lower levels of HDL (123). It is possible that oxidized LDL and low HDL impart increased susceptibility to infection, although the combination of infections and an adverse serum lipid profile may both result from an undesirable diet, i.e., more sugar and fewer healthy fats.

Food processors generally add large amounts of sugar to fat-free or low-fat foods to make them more palatable to consumers. Fructose is 1 dietary constituent that is consistently found to have adverse health consequences, and the larger the proportion of fructose is in the diet, the more formidable the effect. The adverse effects of fructose that have been documented include increased serum triglycerides, particularly in men (124125); increased serum uric acid, which is associated with gout and hypertension (126); increased lipid peroxidation (57) and increased oxidation of LDL (127); increased oxidative stress in animal models (128); greater risk of the development of metabolic syndrome, including obesity, insulin resistance, hypertension, and CVD risk (129130); increased nonalcoholic fatty liver disease (131); and increased systemic inflammation and associated renal disease (132).

There are clearly many established physiological mechanisms by which fructose increases CVD and several other diseases. Whether the source of dietary fructose is sucrose or HFCS would seem irrelevant, although sucrose is 50% fructose, whereas the most common dietary source of HFCS (soft drinks) is generally 55% fructose and ∼43% glucose. Solutions of fructose are also highly susceptible to autoxidation, producing a host of toxic products (57), whereas sucrose is highly resistant to oxidation. The toxic products from fructose oxidation include formaldehyde and α-dicarbonyls. Although saturated fats have been implicated in many of the adverse health effects attributed to fructose, there is no scientific evidence to support a role for saturated fats in the physiological mechanisms. On the other hand, plausible mechanisms are proposed for all of the unhealthy conditions promoted by high fructose intake mentioned earlier.

It turns out that a high level of fructose in the diet increases plasma triglycerides, which leads to not only increased levels of VLDL and small, dense LDL particles, but increased levels of oxidized LDL, insulin resistance, and other metabolic consequences linked to metabolic syndrome and dyslipidemia (133). The mechanisms by which fructose promotes inflammation and elevated levels of uric acid and several cytokines have been reviewed (132).

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Conclusions

Saturated fats are benign with regard to inflammatory effects, as are the MUFAs. The meager effect that saturated fats have on serum cholesterol levels when modest but adequate amounts of polyunsaturated oils are included in the diet, and the lack of any clear evidence that saturated fats are promoting any of the conditions that can be attributed to PUFA makes one wonder how saturated fats got such a bad reputation in the health literature. The influence of dietary fats on serum cholesterol has been overstated, and a physiological mechanism for saturated fats causing heart disease is still missing.

Various aldehydes produced in the oxidation of PUFAs, as well as sugars, are known to initiate or augment several diseases, such as cancer, inflammation, asthma, type 2 diabetes, atherosclerosis, and endothelial dysfunction. Saturated fats per se may not be responsible for many of the adverse health effects with which they have been associated; instead, oxidation of PUFAs in those foods may be the cause of any associations that have been found. Consequently, the dietary recommendations to restrict saturated fats in the diet should be revised to reflect differences in handling before consumption, e.g., dairy fats are generally not heated to high temperatures. It is time to reevaluate the dietary recommendations that focus on lowering serum cholesterol and to use a more holistic approach to dietary policy.

Eat less saturated fat

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Practical tips to help you cut down on the amount of fat in your diet, including saturated fat.

Eating a diet that is high in saturated fat can raise the level of cholesterol in the blood. Having high cholesterol increases the risk ofheart disease

Saturated fat is the kind of fat found in butter and lard, pies, cakes and biscuits, fatty cuts of meat, sausages and bacon, and cheese and cream.

We’re advised to eat less fat, especially saturated fat. UK health guidelines recommend that:

  • the average man should eat no more than 30g of saturated fat a day
  • the average woman should eat no more than 20g of saturated fat a day

You can use these figures to guide your choices when you're shopping. When you look at nutrition labels, you can see how easy it is to eat too much fat.

You can learn more about fat, including the different kinds of fat and their impact on our health, in Fat: the facts.

Tips on eating less fat

These tips can help you cut the total amount of fat in your diet:

  • Compare nutrition labels when shopping, so you can pick foods lower in fat.
  • Ask your butcher for lean cuts of meat, or compare nutrition labels on meat packaging. Look for meat that has visibly less fat.
  • Choose lower-fat dairy products, such as 1% fat milk, low-fat plain yoghurt or reduced-fat cheese.
  • Grill, bake, poach or steam food rather than deep frying or roasting.
  • Measure oil with a tablespoon or use an oil spray, rather than pouring it straight from a container.
  • Trim visible fat and take skin off meat before cooking.
  • Use the grill instead of the frying pan, whatever meat you’re cooking.
  • Put more vegetables or beans in casseroles and stews and curries, and a bit less meat.
  • Spoon off fats and oils from roasts, casseroles, stews and curries.
  • When making sandwiches, try leaving out the butter or spread: you might not need it if you're using a moist filling.
  • Try reduced-fat spreads, such as olive oil or sunflower spreads (a new manufacturing process solved past concerns about their trans fat content). 

Cutting down on saturated fat

Use these practical tips about common foods to help you cut down on saturated fat:

Read the label

Nutrition labels can help you cut down on saturated fat. Look out for "saturates" or "sat fat" on the label.

High: More than 5g saturates per 100g. May be colour-coded red.

Low: 1.5g saturates or less per 100g. May be colour-coded green.

Medium: If the amount of saturated fat per 100g is in between these figures, that is a medium level, and may be colour-coded amber.

The label below is an example provided by a leading supermarket, which shows clearly that the food is high in saturated fat, because the saturates section is colour-coded red.

At home

  • Spaghetti bolognese: use a lower-fat mince, as it’s lower in saturated fat. If you aren't using lower-fat mince, brown the mince first, then drain off the fat before adding other ingredients.
  • Pizza: choose a lower-fat topping, such as vegetables, ham, fish or prawns, instead of pepperoni, salami or extra cheese.
  • Fish pie: use reduced-fat spread and 1% fat milk. Try this healthy fish pie recipe.
  • Chilli: use lower-fat mince to reduce the saturated fat content. Or try it vegetarian-style by adding beans, pulses and vegetables, instead of mince. Try this healthy chilli con carne recipe.
  • Ready meals: compare the nutrition labels on different ready meals. There can be a big difference in saturated fat content. Pick the one lower in saturated fat using per 100g or per serving information. Remember, serving size may vary, so read the label carefully.
  • Potatoes: make your roast potatoes healthier by cutting them into larger pieces than usual and using just a little sunflower or olive oil.
  • Chips: choose thick, straight-cut chips instead of french fries or crinkle-cut. If you’re making your own, cook them in the oven with a little sunflower oil, rather than deep frying.
  • Mashed potato: use reduced-fat spread instead of butter, and 1% fat milk or skimmed milk instead of whole or semi-skimmed milk.
  • Chicken: before you eat it, take the skin off to reduce the saturated fat content. Try this healthy lemon chicken recipe.
  • Meat: trim the visible fat off meat such as steak.
  • Sausages: compare nutrition labels on the packs and choose the ones lower in saturated fat using per serving or per 100g information. Remember, servings may vary, so read the label carefully. Make sure you grill them instead of frying.
  • Bacon: choose back bacon instead of streaky bacon. If you’re cooking your own, grill the bacon instead of frying.
  • Eggs: prepare eggs without oil or butter. Poach, boil or dry fry your eggs.
  • Pasta: try a tomato sauce on your pasta. It’s lower in saturated fat than a creamy or cheesy sauce.
  • Milk: use 1% fat milk on your cereal. It has about half the saturated fat of semi-skimmed.
  • Cheese: when using cheese to flavour a dish or sauce, try a strong-tasting cheese, such as mature cheddar, because you’ll need less. Make cheese go further by grating instead of slicing it.
  • Yoghurt: choose a lower-fat and lower-sugar yoghurt. There can be a big difference between different products. 

Out and about

The tips below can help you cut down on saturated fat when eating out.

  • Coffee on the go: swap any large whole milk coffee for regular "skinny" ones.
  • Curry: go for dry or tomato-based dishes, such as tandoori or madras, instead of creamy curries, such as korma, pasanda or masala. Choose plain rice and chapatti instead of pilau rice and naan.
  • Kebabs: at the kebab shop go for a shish kebab with pitta bread and salad, rather than a doner kebab.
  • Chinese takeaway: choose a lower-fat dish, such as steamed fish, chicken chop suey or Szechuan prawns.
  • Thai: try a stir-fried or steamed dish containing chicken, fish or vegetables. Watch out for curries that contain coconut milk, which is high in saturated fat. If you choose one of these, try not to eat all the sauce.
  • Snack time: have some fruit, toast, a low-fat and lower-sugar yoghurt or a small handful of unsalted nuts, instead of chocolate, doughnuts, croissants or pastries. If you must have something sweet, swap cakes and biscuits for a currant bun, scone or some malt loaf, plain or with reduced-fat spread. Try these healthier food swaps

Page last reviewed: 01/06/2015

Next review due: 01/06/2017

Fat: the facts

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Too much fat in your diet, especially saturated fats, can raise your cholesterol, which increases the risk of heart disease. 

Current UK government guidelines advise cutting down on all fats and replacing saturated fat with some unsaturated fat. 

In recent years, the popular media has turned the debate about the causes of major public health issues such as heart diseasediabetesand obesity into something of a "fat versus sugar" dogfight.

But the question should not be about choosing between fat or sugar: there are good reasons for cutting down on both.

Cutting down on saturated fats is only one aspect of reducing your risk of heart disease, stroke and other cardiovascular diseases. Other risk factors include eating too much salt and sugar, being overweight,smoking and a lack of physical activity.

When it comes to heart health, you are better off focusing on your overall diet than on individual nutrients such as fat or sugar. Abalanced and nutritious diet is considered one of the best ways to reduce your risk of developing cardiovascular diseases.

Not all fat is bad

A small amount of fat is an essential part of a healthy, balanced diet. Fat is a source of essential fatty acids such as omega-3 – "essential" because the body can't make them itself.

Fat helps the body absorb vitamins AD and E. These vitamins are fat-soluble, meaning they can only be absorbed with the help of fats.

The fat you eat is broken down during digestion into smaller units of fat called fatty acids. Any fat not used by your body’s cells or to create energy is converted into body fat. Likewise, unused carbohydrate and protein are also converted into body fat.

All types of fat are high in energy. A gram of fat, whether saturated or unsaturated, provides 9kcal (37kJ) of energy compared with 4kcal (17kJ) for carbohydrate and protein.

The main types of fat found in food are saturated fats and unsaturated fats. Most fats and oils contain both saturated and unsaturated fats in different proportions.

As part of a healthy diet, we should try to cut down on foods and drinks high in saturated fats and trans fats and replace some of them with unsaturated fats.

Frequently eating more energy than you need, whether it’s from fat, carbohydrate or protein, increases your risk of becoming overweight or obese, which can increase your cholesterol.

Saturated fats

Saturated fats are found in many foods, both sweet and savoury. Most of them come from animal sources, including meat and dairy products, as well as some plant foods such as palm oil.

Foods high in saturated fats include:

  • fatty cuts of meat
  • meat products, including sausages and pies
  • butter, ghee and lard
  • cheese, especially hard cheese
  • cream, soured cream and ice cream
  • some savoury snacks and chocolate confectionery
  • biscuits, cakes and pastries
  • palm oil
  • coconut oil and cream

'Sat fat' health risks

While any type of fat in our food can be turned into cholesterol by the body, it's the "sat fat" we need to cut down on because we're eating too much of it.

Cholesterol is mostly made in the liver from any type of fat you eat. It's carried in the blood in two ways: as low density lipoprotein (LDL) and high density lipoprotein (HDL).

Too much LDL cholesterol can lead to fatty deposits developing in the arteries, which can restrict the flow of blood to the heart and brain, increasing the risk of heart disease and stroke.

On the other hand, HDL cholesterol has a positive effect by taking cholesterol from parts of the body where there is too much of it, to the liver, where it is disposed of.

Eating too much fat and sugar can also increase the level of triglycerides, a fatty substance mostly made by the liver. High levels of triglycerides in the blood have also been linked with narrowing of the arteries.

Saturated fat guidelines

Most people in the UK eat too much saturated fats. The population on average gets 12.6% of their energy (kJ/kcal) from saturated fats, which is slightly above the 11% maximum recommended by the government.

  • The average man should aim to have no more than 30g of saturated fat a day.
  • The average woman should aim to have no more than 20g of saturated fat a day.
  • Children should have less.

Trans fats

Trans fats are found naturally at low levels in some foods, such as those from animals, including meat and dairy products.

Trans fats can also be found in hydrogenated vegetable oil. Hydrogenated vegetable oil must be declared on a food's ingredients list if present.

Like saturated fats, trans fats can raise cholesterol levels in the blood. This is why it's recommended that trans fats should make up no more than 2% of the energy (kJ/kcal) we get from our diet. For adults, this is no more than about 5g a day.

However, most people in the UK don't eat a lot of trans fats. On average, we eat about half the recommended maximum. Most of the supermarkets in the UK have removed hydrogenated vegetable oil from all their own-brand products.

We eat a lot more saturated fats than trans fats. This means that when looking at the amount of fat in your diet, it's more important to focus on reducing the amount of saturated fats.

Unsaturated fats

If you want to cut your risk of heart disease, it's best to reduce your overall fat intake and swap saturated fats for unsaturated fats. There is good evidence that replacing saturated fats with unsaturated fats can help lower cholesterol.

Found primarily in oils from plants, unsaturated fats can be either polyunsaturated or monounsaturated. Monounsaturated fats help protect our hearts by maintaining levels of HDL cholesterol while reducing levels of LDL cholesterol.

Monounsaturated fats are found in:

  • olive oil, rapeseed oil and their spreads
  • avocados
  • some nuts, such as almonds, brazils and peanuts

Polyunsaturated fats can help lower the level of LDL cholesterol. Replacing saturated fats with polyunsaturated fats may also help reduce triglyceride levels.

There are two types of polyunsaturated fats: omega-3 and omega-6. Some types of omega-3 and omega-6 fats cannot be made by the body and are therefore essential in small amounts in the diet.

Omega-6 fats are found in vegetable oils such as rapeseed, corn, sunflower and some nuts. Omega-3 fats are found in oily fish such as mackerel, kippers, herring, trout, sardines, salmon and fresh tuna.

While most of us get sufficient omega-6 in our diet, mostly from cooking oil, we're advised to eat more omega-3 by eating at least twoportions of fish a week, including one of oily fish.

Vegetable sources of omega-3 fats are not thought to have the same benefits on heart health as those found in fish.

Buying lower fat

There are labelling guidelines set by the European Union to help you work out whether or not a food is high in fat and saturated fat.

The nutrition labels on food packaging can help you cut down on total fat and saturated fat (also listed as saturates, or sat fat).

Total fat

  • high fat – more than 17.5g of fat per 100g
  • low fat – 3g of fat or less per 100g, or 1.5g of fat per 100ml for liquids (1.8g of fat per 100ml for semi-skimmed milk)
  • fat-free – 0.5g of fat or less per 100g or 100ml

Saturated fat

  • high in sat fat – more than 5g of saturates per 100g
  • low in sat fat – 1.5g of saturates or less per 100g or 0.75g per 100ml for liquids
  • sat fat-free – 0.1g of saturates per 100g or 100ml

'Lower fat' labels

For a product to be labelled lower fat, reduced fat, lite or light, it has to contain at least 30% less fat than a similar product.

But if the type of food in question is high in fat in the first place, the lower-fat version may also still be high in fat (17.5g or more of fat per 100g). For example, a lower-fat mayonnaise is 30% lower in fat than the standard version, but is still high in fat.

These foods also aren't necessarily low in calories. Sometimes the fat is replaced with sugar and may end up with a similar energy content. To be sure of the fat content and the energy content, remember to check the nutrition label on the packet.

Cutting down on fat is only one aspect of achieving a healthy diet. Find out more about how to get a balanced nutritious diet in the eatwell plate.

Page last reviewed: 30/04/2015

Next review due: 30/04/2017

Fats explained

Oil in bottles

All fats are high in calories, so it’s important to bear this in mind if you are watching your weight.

In terms of your heart, it’s important to think about the type of fat you are eating.

A typical diet is made up of different types of fat. While you need to make sure you eat foods that contain healthy monounsaturated and polyunsaturated fats, too much saturated fat can increase the amount of cholesterol in your blood, which can increase your risk of developing coronary heart disease.

You can have a high cholesterol level even if you are a healthy weight. And even if your cholesterol level is healthy, it’s important to eat well and to be active to keep your heart healthy. 

Choosing fats

Monounsaturated and polyunsaturated fats provide essential fatty acids and fat soluble vitamins - so they’re an important part of your diet.  

Wherever possible replace saturated fats with small amounts of monounsaturated and polyunsaturated fats.  

The average man should have no more than 30g of saturated fat a day, and the average woman no more than 20g a day.

Type of fats

 

Found in

Monounsaturated

Have these in small amounts. They can help to maintain healthy cholesterol levels. 
  Avocados, olives, olive oil, rapeseed oil. Almonds, cashews, hazelnuts, peanuts, pistachios and spreads made from these nuts.

Polyunsaturated

Have these in small amounts. Polyunsaturated fats help to maintain healthy cholesterol levels and provide essential fatty acids.
Oily fish, corn oil, sesame oil, soya oil, and spreads made from those oils. Flaxseed, pine nuts, sesame seeds, sunflower seeds, and walnuts. 

Saturated

Swap these for unsaturated fats. Eating too much saturated fat increases the amount of cholesterol in your blood.
Processed meats like sausages, ham, burgers. Fatty meat. Hard cheeses including cheddar. Whole milk and cream. Butter, lard, ghee, suet, palm oil and coconut oil.

Trans

Avoid wherever possible. They can increase cholesterol in your blood. Foods with hydrogenated oils or fats in them likely contain trans fats. 
Fried foods, takeaways, snacks like biscuits, cakes or pastries. Hard margarines.

Saturated fat guidelines

At the moment UK guidelines encourage us to swap saturated fats for unsaturated fats.  You might have seen reports about a study we helped to fund which suggests there’s not enough evidence to back the current UK guidelines on the types of fat we eat. We think more research is needed before suggesting any major changes to healthy eating guidance.

Top tips to help you reduce your saturated fat

  • Swap butter, lard, ghee and coconut and palm oils with small amounts of monounsaturated and polyunsaturated fats, such as olive, rapeseed or sunflower oils and spreads.  
  • Choose lean cuts of meat and make sure you trim any excess fat and remove the skin from chicken and turkey.
  • Instead of pouring oils straight from the bottle, use a spray oil or measure out your oils with a teaspoon.
  • Read food labels to help you make choices that are lower in saturated fat.
  • Opt to grill, bake, steam, boil or poach your foods.  
  • Make your own salad dressings using ingredients like balsamic vinegar, low fat yoghurt, lemon juice, and herbs, with a dash of olive oil.  
  • Use semi-skimmed, 1% or skimmed milk rather than whole or condensed milk.
  • Cottage cheese, ricotta and extra light soft cheese are examples of lower fat cheese options. Remember that many cheeses are high in saturated fat so keep your portions small - matchbox sized. Opt for strongly flavoured varieties and grate it to make a little go a long way

Dietary fats: Know which types to choose

When choosing fats, pick unsaturated fat over saturated or trans fat. Here's how to know the difference.

By Mayo Clinic Staff

Most foods contain several different kinds of fat, and some are better for your health than others. You don't need to completely eliminate all fat from your diet. In fact, some fats actually help promote good health. But it's wise to choose the healthier types of dietary fat and then enjoy them — in moderation.

The facts about fat

There are numerous types of fat. Your body makes its own fat from taking in excess calories. Some fats are found in foods from plants and animals and are known as dietary fat. Dietary fat is a macronutrient that provides energy for your body. Fat is essential to your health because it supports a number of your body's functions. Some vitamins, for instance, must have fat to dissolve and nourish your body.

But there is a dark side to fat. Fat is high in calories and small amounts can add up quickly. If you eat more calories than you need, you will gain weight. Excess weight is linked to poor health.

The concern with some types of dietary fat (and their cousin cholesterol) is that they are thought to play a role in cardiovascular disease and type 2 diabetes. Dietary fat also may have a role in other diseases, including obesity and cancer.

Research about the possible harms and benefits of dietary fat is always evolving. And a growing body of research suggests that when it comes to dietary fat, you should focus on eating healthy fats and avoiding unhealthy fats. Simply stated, fat is made up of varying amounts of fatty acids. It's the type and amount of fatty acid found in food that determines the effect of the fat on your health.

Harmful dietary fat

There are two main types of potentially harmful dietary fat — fat that is mostly saturated and fat that contains trans fat:

  • Saturated fat. This is a type of fat that comes mainly from animal sources of food, such as red meat, poultry and full-fat dairy products. Saturated fat raises total blood cholesterol levels and low-density lipoprotein (LDL) cholesterol levels, which can increase your risk of cardiovascular disease. Saturated fat may also increase your risk of type 2 diabetes.
  • Trans fat. This is a type of fat that occurs naturally in some foods in small amounts. But most trans fats are made from oils through a food processing method called partial hydrogenation. By partially hydrogenating oils, they become easier to cook with and less likely to spoil than do naturally occurring oils. Research studies show that these partially hydrogenated trans fats can increase unhealthy LDL cholesterol and lower healthy high-density lipoprotein (HDL) cholesterol. This can increase your risk of cardiovascular disease.

Most fats that have a high percentage of saturated fat or that contain trans fat are solid at room temperature. Because of this, they're typically referred to as solid fats. They include beef fat, pork fat, butter, shortening and stick margarine.

Healthier dietary fat

The types of potentially helpful dietary fat are mostly unsaturated:

  • Monounsaturated fat. This is a type of fat found in a variety of foods and oils. Studies show that eating foods rich in monounsaturated fats (MUFAs) improves blood cholesterol levels, which can decrease your risk of heart disease. Research also shows that MUFAs may benefit insulin levels and blood sugar control, which can be especially helpful if you have type 2 diabetes.
  • Polyunsaturated fat. This is a type of fat found mostly in plant-based foods and oils. Evidence shows that eating foods rich in polyunsaturated fats (PUFAs) improves blood cholesterol levels, which can decrease your risk of heart disease. PUFAs may also help decrease the risk of type 2 diabetes.
  • Omega-3 fatty acids. One type of polyunsaturated fat is made up of mainly omega-3 fatty acids and may be especially beneficial to your heart. Omega-3, found in some types of fatty fish, appears to decrease the risk of coronary artery disease. It may also protect against irregular heartbeats and help lower blood pressure levels. There are plant sources of omega-3 fatty acids. However, the body doesn't convert it and use it as well as omega-3 from fish.

Foods made up mostly of monounsaturated and polyunsaturated fats are liquid at room temperature, such as olive oil, safflower oil, peanut oil and corn oil. Fish high in omega-3 fatty acids include salmon, tuna, trout, mackerel, sardines and herring. Plant sources of omega-3 fatty acids include flaxseed (ground), oils (canola, flaxseed, soybean), and nuts and other seeds (walnuts, butternuts and sunflower).

A word about cholesterol

Cholesterol isn't a fat. Rather, it's a waxy, fat-like substance. Your body manufactures some cholesterol. Your body also absorbs some dietary cholesterol — cholesterol that's found in foods of animal origins, such as meat and eggs. Cholesterol is vital because, among other important functions, it helps build your body's cells and produces certain hormones. But your body makes enough cholesterol to meet its needs — you don't need any dietary cholesterol.

Excessive cholesterol in your diet can increase your unhealthy LDL cholesterol level, although not as much as saturated fat does. This can increase your risk of heart disease and stroke. Most foods that contain saturated fat also contain cholesterol. So cutting back on these foods will help decrease both saturated fat and cholesterol. The exception to this is tropical oils, which are high in saturated fat but contain no cholesterol.

Recommendations for fat intake

Because some dietary fats are potentially helpful and others potentially harmful to your health, it pays to know which ones you're eating and whether you're meeting national recommendations. The Dietary Guidelines for Americans offer recommendations about dietary fat intake.

Here's a look at the recommendations and common sources of each type of dietary fat. Be aware that many foods contain different kinds of fat and varying levels of each type. For example, butter contains unsaturated fats, but a large percentage of the total fat is saturated fat. And canola oil has a high percentage of monounsaturated fat but also contains smaller amounts of polyunsaturated and saturated fat.

Type of fat Recommendation
Total fat This includes all types of dietary fat. Limit total fat intake to 20 to 35 percent of your daily calories. Based on a 2,000-calorie-a-day diet, this amounts to about 44 to 78 grams of total fat a day.
Monounsaturated fat While no specific amount is recommended, the guidelines recommend eating foods rich in this healthy fat while staying within your total fat allowance.
Polyunsaturated fat While no specific amount is recommended, the guidelines recommend eating foods rich in this healthy fat while staying within your total fat allowance.
Omega-3 fatty acids While no specific amount is recommended, the guidelines recommend eating foods rich in this healthy fat while staying within your total fat allowance.
Saturated fat Limit saturated fat to no more than 10 percent of your total calories. Limit to 7 percent to further reduce your risk of heart disease. Based on a 2,000-calorie-a-day diet, a 10 percent limit amounts to about 22 grams of saturated fat a day, while 7 percent is about 15 grams. Saturated fat intake counts toward your total daily allowance of fat.
Trans fat No specific amount is recommended, but the guidelines say the lower the better. Avoid trans fat by looking at food labels and by checking for the term "partially hydrogenated."
Cholesterol Less than 300 milligrams a day. Less than 200 milligrams a day if you're at high risk of cardiovascular disease.

DIETARY GUIDELINES FOR AMERICANS, 2010

Need help calculating what your daily fat intake should be in grams? Multiply your daily total calorie intake by the recommended percentage of fat intake. Divide that total by 9, which is the number of calories in a gram of fat. For example, here's how a 7 percent saturated fat limit looks if you eat 2,000 calories a day. Multiply 2,000 by 0.07 to get 140 calories. Divide 140 by 9 to get about 15 grams of saturated fat.

What about very low-fat diets?

If watching fat content is a good strategy, is it even better to try to eliminate all fat from your diet? No. First, your body needs some fat — the healthy fats — to function normally. If you try to avoid all fat, you risk getting insufficient amounts of fat-soluble vitamins and essential fatty acids.

Also, in attempting to remove fat from your diet, you may wind up eating too many processed foods touted as low-fat or fat-free rather than healthier and naturally lower fat foods, such as fruits, vegetables, legumes and whole grains. Instead of doing away with fat in your diet, enjoy healthy fats in moderation.

Tips for choosing foods with the best types of dietary fat

So now that you know which types of dietary fat are healthy or unhealthy, and how much to include, how do you adjust your diet to meet dietary guidelines?

First, focus on reducing foods high in saturated fat, trans fat and cholesterol. Then emphasize food choices that include plenty of monounsaturated fats (MUFAs) and polyunsaturated fats (PUFAs). But a word of caution — don't go overboard even on healthy fats. All fats, including the healthy ones, are high in calories. So consume MUFA-rich and PUFA-rich foods instead of other fatty foods, not in addition to them.

Here are some tips to help you make over the fat in your diet:

  • Use the Nutrition Facts label when selecting foods. Read food labels and look for the amount of trans fat listed. By law a serving of food containing less than 0.5 grams of trans fat can be labeled as 0 grams. Therefore, it is important to also check ingredient lists for the term "partially hydrogenated." It's best to avoid foods that contain trans fat and those that have been partially hydrogenated.
  • Prepare fish, such as salmon and mackerel, instead of meat at least twice a week to get a source of healthy omega-3 fatty acids. Limit sizes to 4 ounces of cooked seafood a serving, and bake or broil seafood instead of frying.
  • Use liquid vegetable oil instead of solid fats. For example, saute with olive oil instead of butter, and use canola oil when baking.
  • Use olive oil in salad dressings and marinades.
  • Use egg substitutes instead of whole eggs when possible.
  • Select milk and dairy products that are low in fat.
Comparative properties of common cooking fats (per 100 g )
Type of fat Total fat (g) Sat(g) Mono (g) Poly (g) Smoke point
Sunflower oil 100 11 20 69 225 °C (437 °F)[9]
Sunflower oil (high oleic) 100 12 84 [10] [10]
Soybean oil 100 16 23 58 257 °C (495 °F)[9]
Canola oil 100 7 63 28 205 °C (401 °F)[10][11]
Olive oil 100 14 73 11 190 °C (374 °F)[9]
Corn oil 100 15 30 55 230 °C (446 °F)[9]
Peanut oil 100 17 46 32 225 °C (437 °F)[9]
Rice bran oil 100 25 38 37 250 °C (482 °F)[12]
Vegetable shortening (hydrogenated) 71 23 8 37 165 °C (329 °F)[9]
Lard 100 39 45 11 190 °C (374 °F)[9]
Suet 94 52 32 3 200 °C (392 °F)
Butter 81 51 21 3 150 °C (302 °F)[9]
Coconut oil 100 86 6 2 177 °C (351 °F)

เมื่อใช้ความร้อนน้ำมันมะกอก และน้ำมันคาโนล่าจะเกิดสาร Aldehydes น้อยกว่าน้ำมันดอกทานตะวันและน้ำมันข้าวโพด 20 เท่า สาร Aldehydes นี้จะเป็นสารที่ทำให้เกิดมะเร็งไม่ว่าจะเกิดจากการสูดดมหรือการรับประทาน

การใช้น้ำมันอย่าปลอดภัย

  • ลดการรับประทานอาหารทอด โดยเฉพาะการทอดที่มีอุณหภูมิสูงมาก เช่นการทอดน้ำมันท่วม
  • ควรจะใช้น้ำมันที่มีไขมันไม่อิ่มตัวหนึ่งตำแหน่งเช่นน้ำมันมะกอกหรือไขมันอิ่มตัว(เช่นน้ำมันมะพร้าว) แทนไขมันไม่อิ่มตัวหลายตำแหน่ง(น้อยกว่าร้อยละ20)
  • น้ำมันควรจะเก็บไว้ไม่ให้ถูกแสง และไม่ควรใช้น้ำมันทอดซ้ำ

สารพิษที่เกิดจากการใช้น้ำมัน

ไขมันไม่อิ่มตัวเชิงซ้อน(หลายตำแหน่ง)มีประโยชน์ในการลดไขมันในเลือดและป้องกันโรคหัวใจ แต่หากเราเก็ยไขมันให้ถูกแสงึ่งทำให้เกิดสารพิษทีละน้อย แต่หากทำอาหารอุณหภูมิมากกว่าจุดเกิดควันก็จะเกิดสารซึ่งทำให้เกิดโรคมะเร็งและหลอดเลือดหัวใจ ส่วนไขมันอิ่มตัวจะทนความร้อนได้ดี แต่เนื่องจากเป็นไขมันิ่มตัวหากรับประทานมากจะทำให้เกิดโรคหัวใจและหลอดเลือด แต่เกิดสารพิษน้อยเมื่อเจอความร้อนสูง

ส่วนไขมันไม่อิ่มตัวเชิงเดี่ยว(หนึ่งตำ)แหน่งหากเป็น extra virgin หรือ virgin หากรับประทานสดจะมีคุณค่าทางอาหารสูง และคุณค่าทางอาหารจะลดลงเมื่อเจอความร้อน แต่เกิดสารพิษไม่มาก

โดยสรุป

  • ไขมันไม่อิ่มตัวเชิงเดียวชนิด extra virgin หรือ virginมีประโยชน์ลดไขมันในเลือดและป้องกันโรคหัวใจ ควรจะใช้ปรุงรสหรือทำเป็นน้ำสลัด หากใช้ผัดหรือทอดคุณค่าทางอาหารจะลดลงแต่เกิดสารพิษไม่มาก
  • ไขมันไม่อิ่มตัวเชิงซ้อน(หลายตำแหน่ง)หากไม่ถูกความร้อนจะมีประโยชน์ในการลดไขมันและป้องกันโรคหัวใจ แต่หากถูกความร้อนหรือเก็บไว้ในที่มีแสงจะก่อให้เกิดสารที่เป็นผลเสียต่อสุขภาพ
  • ส่วนไขมันอิ่มตัวมีผลเสียต่อสุขภาพ แต่สามารถทนความร้อนโดยเกิดสารพิษน้อย

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