Current recommendations concerning rational use of fats. II. Value of polyunsaturated fatty acids from the n-6 and n-3 groups and general recommendations

The number of scientific proofs of a close correlation between health state and diet is increasing. The present suggestions on the consumption of fats and PUFA effect on the human organism are discussed on the basis of current literature and statements of the panel conference on "Fat and cholesterol". The survey of the pertinent literature seems to suggest the following conclusions. Blood lipid level decrease by low-fat diet depends more on the composition of fatty acids than on the total dietary fat content and on replacement of fats with carbohydrates. Long-chain n-3 fatty acids from seafish oil exert a beneficial effect on plasma lipid level. They participate in the mechanisms of blood clotting, inhibit atherosclerosis progression and reduce the arterial blood pressure. In the assessment of the effect of dietary fatty acids on lipid metabolism the dietary content of three groups of fatty acids must be considered: saturated (S), monounsaturated (M) and polyunsaturated (P). Diets containing the same P:S proportions but different amounts of saturated fatty acids produce various effects on the blood cholesterol level. The need is perceived of making the population aware of the importance of rational fat consumption and introduction of modifications of food processed by food product industry.     

Total fat and fatty acid intakes and food sources in Mediterranean older adults requires education to improve health

The proportion of fat has increased at the expense of carbohydrates in the past years, and we aimed to assess total fat and fatty acids intake and their food sources among Mediterranean older adults and compare them to national and international recommendations. This study was conducted in 211 participants to determine lipid and fatty acid intake using a Spanish food database. The mean daily intake of lipids was 68.6 g/d (standard deviation [SD]: 24.6; 34.4%, SD: 7.0 of total energy consumed). Men, younger participants, and those with higher education ingested more lipids than their peers. Fatty acids were ingested as follows (expressed as percentage of total energy intake): monounsaturated fatty acids (MUFA) (16.7%, SD: 4.1), saturated fatty acids (SFA) (9.6%, SD: 2.6), and polyunsaturated fatty acids (PUFA) (5.0%, SD: 1.7). Oils and seeds were the highest contributors in the intake of lipids (38.8%, SD: 16.0), MUFA (53.9%, SD: 18.7), and PUFA (33.0%, SD: 16.4). The total fat intake (34.4%, SD: 7.0) was within the range of International and Spanish recommendations among Mediterranean older adults; however, the intake of fatty acids did not abide by the international (PUFA) and Spanish recommendations (SFA, MUFA). α-Linoleic acid, eicosapentaenoic acid, and docosahexaenoic acid intake were lower than recommendations, but cholesterol intake (243.9 mg, SD: 140.4) was within the range of recommendations. Therefore, public health campaigns are needed to encourage older adults to decrease SFA intake and increase adherence to the Mediterranean diet pattern for a better health.     

Contribution of specific foods to fat, fatty acids, and cholesterol in the development of a food frequency questionnaire in Koreans

The present study identified dietary sources of fat, fatty acids, and cholesterol in Koreans residing in and near Seoul. The study also identified foods to be included in a food frequency questionnaire (FFQ) by both contribution analysis (CA) and multiple regression analysis (MRA). Three-day dietary records were collected from 224 subjects (107 men and 117 women) aged 30 to 85 years. Pork was the main source of total fat and the largest contributor to saturated fatty acids (SFA) was beef. MRA identified animal food as the primary source of between-person variance for SFA. Arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid originated primarily from marine products. About a fourth of the total cholesterol intake was derived from chickens' eggs by CA, while chickens' eggs accounted for 46% of the cholesterol intake for between-person variance by MRA. With 10 food items, the FFQ could explain more than half of total intakes except for total fat and n-3 polyunsaturated fatty acids (PUFA), and at least 65% of between-person variances. The percentage coverage in the FFQ ranged from 61% for n-6 PUFA and linoleic acid and to 90% for arachidonic acid. The value of this FFQ is that it can estimate usual dietary food patterns and nutrient intake in Koreans for epidemiological studies. It can also potentially be used to study the relationship between specific diseases and nutrient intakes of interest.     

Pork with a high content of polyunsaturated fatty acids lowers LDL cholesterol in women

BACKGROUND: Animal products contribute significantly to the saturated fat and cholesterol content of the American diet. Contrary to dietary advice, consumers have not limited their consumption of animal products. Thus, an alternative approach might be to modify the fatty acid composition of animal products. OBJECTIVE: We tested the hypothesis that modified pork with a high content of polyunsaturated fatty acids (PUFAs) and a low content of saturated fatty acids (SFAs) would lower plasma LDL-cholesterol concentrations in women. DESIGN: Twenty women aged 19-24 y completed a crossover study with 2 diets. Nutritionally complete diets containing 42% of energy from fat differed only in the inclusion of either standard or modified pork. Venous blood samples were collected at weeks 0, 4, and 8. RESULTS: The diet containing modified pork significantly lowered total plasma (P < 0.0076) and LDL (P < 0.0382) cholesterol. The modified diet also resulted in an increase in the PUFA and a decrease in the SFA and monounsaturated fatty acid contents of the cholesteryl ester, free fatty acid, phospholipid, and triacylglycerol lipid classes in both plasma and erythrocytes. Plasma concentrations of glucose, insulin, triacylglycerol, and free fatty acids did not change significantly. CONCLUSIONS: Consumption of pork with a high PUFA content resulted in a decrease in the subjects' total plasma and LDL cholesterol and shifted the fatty acid composition from SFAs to PUFAs in the plasma and erythrocytes. Modification of the fatty acid composition of animal foods will be a useful approach to lowering the saturated fat consumption of Americans.     

Towards improved fat intake and nutrition for Malaysians

An examination of the fat composition of the diet of a Malaysian urban hostel population obtained by chemical analysis of representative meals prepared by a 7-day rotation menu, revealed both nutritional attributes and limitations when compared against the dietary messages contained in the American Heart Association (AHA) and World Health Organisation (WHO) models. The Malaysian diet supplies 26% kcal i.e. 66 g total fat (51 g vegetable fats, 15 g animal fats) and contains <300 mg cholesterol, which are below the upper limits for these dietary constituents in the AHA and WHO models and conflicts with the perception that Malaysians in general, may be consuming too much fat and cholesterol. The supply of essential fatty acids (EFA), however, appears sub-optimal at 3.2% kcal mainly due to the comparatively low content of both the omega-6 (linoleic acid) and omega-3 [alpha-linolenic, eicosapentaenoate (EPA) and docosahexaenoate (DHA)] fatty acids in the Malaysian diet. The estimated omega-6/omega-3 fatty acid ratio of 10 further reflects an imbalance of these two families of polyunsaturated fatty acids (PUFA), which can be corrected to a ratio of 5 to 7 by moderate increases in the consumption of fish, soyabean-based foods, and pulses and nuts. Considering the current status of knowledge on the health effects of the different families of fatty acids, the ratio of 2:3:1 for the saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and PUFA in the diet is judged to improve fat intake and nutrition in Malaysians. Such a dietary fatty acids ratio can be satisfied by the use of a cooking oil containing 28% SFA, 53% MUFA, and 19% PUFA, which may obtained by the judicious blending of palm olein with MUFA-rich and PUFA-rich vegetable oils. Alternatively, moderate increases in the consumption of marine fish, pulses, nuts, soybean-based foods and their products would also serve the same end.     

Comparison of dietary fat and fatty acid intake estimated by the duplicate diet collection technique and estimated dietary records

Introduction A high saturated fatty acid intake is a well recognized risk factor for coronary heart disease development. More recently a high intake of n‐6 polyunsaturated fatty acids (PUFA) in combination with a low intake of the long chain n‐3 PUFA, eicosapentaenoic acid and docosahexaenoic acid has also been implicated as an important risk factor. Aim To compare total dietary fat and fatty acid intake measured by chemical analysis of duplicate diets with nutritional database analysis of estimated dietary records, collected over the same 3‐day study period. Methods Total fat was analysed using soxhlet extraction and subsequently the individual fatty acid content of the diet was determined by gas chromatography. Estimated dietary records were analysed using a nutrient database which was supplemented with a selection of dishes commonly consumed by study participants. Results Bland & Altman statistical analysis demonstrated a lack of agreement between the two dietary assessment techniques for determining dietary fat and fatty acid intake. Conclusion The lack of agreement observed between dietary evaluation techniques may be attributed to inadequacies in either or both assessment techniques. This study highlights the difficulties that may be encountered when attempting to accurately evaluate dietary fat intake among the population.     

Fatty acids and CHD

During the last century much evidence has accumulated to suggest that from a public health perspective the type of fat is more important than the amount of fat. Saturated and trans-fatty acids increase and both n-6 and n-3 PUFA decrease the risk of CHD. Most of the knowledge about the effects of dietary fatty acids on CHD risk is based on observational studies and controlled dietary experiments with intermediate end points (e.g. blood lipoprotein fractions). Information from high-quality randomised controlled trials on fatty acids and CHD is lacking. The Netherlands Institute for Public Health has calculated the potential health gain that can be achieved if the fatty acid composition of the current Dutch diet is replaced by the recommended fatty acid composition. The recommendations of The Netherlands Health Council are: saturated fatty acids <10% energy intake; trans-fatty acids <1% energy intake; fish consumption (an indicator of n-3 PUFA) once or twice weekly. Implementation of this recommendation could reduce the incidence of CHD in The Netherlands by about 25,000/year and the number of CHD-related deaths by about 6000/year and increase life expectancy from age 40 years onwards by 0.5 year. These projections indicate the public health potential of interventions that modify the fatty acid composition of the diet.     

Substitution of saturated with monounsaturated fat in a 4-week diet affects body weight and composition of overweight and obese men

A randomised crossover study of eight overweight or obese men (aged 24-49 years, BMI 25.5-31.3 kg/m(2)), who followed two diets for 4 weeks each, was performed to determine whether substitution of saturated fat with monounsaturated fat affects body weight and composition. Subjects were provided with all food and beverages as modules (selected ad libitum) of constant macronutrient composition, but differing energy content. The % total energy from saturated fat, monounsaturated fat and polyunsaturated fat was 24, 13 and 3 % respectively on the saturated fatty acid (SFA)-rich diet and 11, 22 and 7 % respectively on the monounsaturated fatty acid (MUFA)-rich diet. MUFA accounted for about 80 % of the unsaturated fats consumed on both diets. Body composition, blood pressure, energy expenditure (resting and postprandial metabolic rates, substrate oxidation rate, physical activity), serum lipids, the fatty acid profile of serum cholesteryl esters and plasma glucose and insulin concentrations were measured before and after each diet period. Significant (P< or =0.05) differences in total cholesterol and the fatty acid composition of serum cholesteryl esters provided evidence of dietary adherence. The men had a lower weight (-2.1 (SE 0.4) kg, P=0.0015) and fat mass (-2.6 (SE 0.6) kg, P=0.0034) at the end of the MUFA-rich diet as compared with values at the end of the SFA-rich diet. No significant differences were detected in energy or fat intake, energy expenditure, substrate oxidation rates or self-reported physical activity. Substituting dietary saturated with unsaturated fat, predominantly MUFA, can induce a small but significant loss of body weight and fat mass without a significant change in total energy or fat intake.     

What are the health effects of fat?

In order to answer the question which health benefits are to be expected from dietary fat, we have to differentiate between different kinds of fat with varying fatty acid composition. Saturated fatty acids are commonly judged to have a negative health impact as they lead to increased serum cholesterol levels and a higher risk of coronary heart disease. Therefore, all recommendations stress the importance to limit the intake of saturated fatty acids. Monounsaturated fatty acids, on the other hand, have a positive impact on the serum lipid profile, lead to decreased LDL-oxidation and favorably influence the metabolism of diabetics. However, it is essential that monounsaturated fatty acids be mainly supplied by plant oils like rape seed or olive oil and not by foods that are simultaneously rich in saturated fatty acids. Concerning polyunsaturated fatty acids, it is important to increase the supply of n-3 fatty acids (ratio of n-6:n-3: about 5:1) as there is substantial evidence for their protective effects. If the fatty acid composition of the diet is optimized, even a total dietary fat content of 35% of total energy intake can be adequate as long as there is enough physical activity and the diet is rich in plant-derived foods like vegetables, fruits, cereals, potatoes, beans and legumes.     

Fat intake, diet variety and health promotion

Different epidemiological studies indicated that the optimization of diet and nutrition combined with healthy life style can decrease the risk and even lead to amelioration of various noncommunicable diseases. Promising food-based dietary guidelines have been recommended in order to improve the nutritional and health status. One of the most popular recommendations is related to the amount (less fat and fat-rich foods) and type of the dietary fat component (less saturated, more polyunsaturated fatty acids, lower n-6:n-3 ratio). An overview on the nutrient intake among different age groups in Austria shows that the general consumption of some food groups--especially those rich in carbohydrates--is too low and that the intake of fat is far beyond the recommended amount of 30% of total energy (E%). The results of the 24-hour recall made among Austrian adults (n = 2,585) showed that about 18% of this population group had a fat intake of 30-35 E%, whereas 60% had an intake higher than 35 E%. Only 24% of the female and male adults had a fat intake lower than 30 E%. A result of this high proportion of fat--in the form of foods rich in fat--in the average total energy consumption is a too low intake of carbohydrates, and foods rich in carbohydrates, respectively. An increasing fat intake is associated with an increasing intake of some nutrients such as vitamin A, E, calcium and zinc, but a decreasing intake of other nutrients like vitamin C, folate, carotenoids and others. The diversity of foods consumed during a day increases with decreasing amount of fat in the diet of adults. People with a high amount of fat in their daily diet show a lower intake of vegetables and fruit, cereal products, carotenoids, folates and dietary fibers, but a higher intake of meat and meat products, milk and milk products, sweets and flummeries as well as saturated fatty acids (SFA) and cholesterol. Of course, a higher variety of food items in the daily diet should not be associated with a higher energy intake. Thus, foods with a high nutrient density (vegetables, fruits, low-fat milk products, whole grain cereals, legumes etc.) are recommended. Finally, it has to be annotated that a high diversity in the daily diet with reduced fat and SFA intake allows a sufficient nutrient intake and is an important approach for health promotion.     

Serum fatty acid, lipid profile and dietary intake of Hong Kong Chinese omnivores and vegetarians

OBJECTIVE: To examine the serum fatty acid and lipid profiles and dietary intake of Hong Kong Chinese omnivores and vegetarians with respect to cardiovascular health. DESIGN: Random population survey stratified by age and sex. SUBJECTS: One-hundred and ninety-four omnivore subjects (81 men, 113 women) age 25-70 y, and 60 ovo-lacto-vegetarian adults (15 men, 45 women) age 30-55 y. MEASUREMENTS: Nutrient quantitation was by a food frequency method. Serum fatty acids were analysed by gas chromatography, and serum lipid by standard laboratory methods. RESULTS: Compared with omnivores, vegetarians had higher serum concentrations of polyunsaturated (PUFA) and monosaturated fatty acids (MUFA), and lower saturated fatty acids (SFA), long chain omega-3 and trans fatty acids (TFA). They also had lower serum cholesterol and higher apoA-1 concentrations, but the LDL/HDL ratio was not different. The ratio of polyunsaturated to saturated fatty acids intake was higher in vegetarians. Compared with results from populations with higher incidences of coronary heart disease, while lower myristic and palmitic acid concentrations and higher eicosapentaneoic (EPA) and docosahexanoic acid (DHA) may partly account for the difference in incidence, linoleic acid concentration was higher. Although the Chinese vegetarian diet may be beneficial for heart health in that antioxidant and fibre intakes are higher and saturated fat lower, the low EPA and DHA due to omission from dietary source and suppressed formation by high linoleic acid level, and the presence of TFA in the diet, may exert an opposite effect. CONCLUSION: There are some favourable features in the serum fatty acid profile in the Hong Kong Chinese population with respect to cardiovascular health, but the consumption of TFA is of concern. The Chinese vegetarian diet also contains some adverse features.     

Relationship of diet to the fatty acid composition of human adipose tissue structural and stored lipids

The habitual intake of 20 healthy free-living subjects was determined by two 7-day food records. Documented fatty acid intakes were utilized to examine the influence of fatty acid intake on fatty acid composition of stored and structural lipids in subcutaneous adipose tissue. Subjects with higher intakes of saturated fatty acids exhibited increased levels of total saturated fatty acids and decreased polyunsaturated fatty acids in adipose tissue triglycerides (p less than 0.01). The dietary P/S ratio was significantly related to the saturated and polyunsaturated content of stored lipids. In the phospholipid fraction, relationships were found between dietary C18:2(6) and the P/S ratio of phosphatidylcholine (p less than 0.05). The essential fatty acid content of the two phospholipids studied was related to the dietary fats consumed. Relationships were identified between major fatty acids in the triglyceride and phospholipid fraction. Although diet was found to relate to fatty acid composition, the structural lipids in human adipose tissue appear more resistant to compositional change than stored triglycerides.     

Dietary n-3 and n-6 fatty acids alter avian metabolism: metabolism and abdominal fat deposition

The effects of dietary saturated fatty acids and polyunsaturated fatty acids (PUFA) of the n-3 and n-6 series on weight gain, body composition and substrate oxidation were investigated in broiler chickens. At 3 weeks of age three groups of chickens (n 30; ten birds per group) were fed the fat-enriched experimental diets for 5 weeks. These diets were isonitrogenous, isoenergetic and contained 208 g protein/kg and 80 g edible tallow, fish oil or sunflower oil/kg; the dietary fatty acid profiles were thus dominated by saturated fatty acids, n-3 PUFA or n-6 PUFA respectively. Resting RQ was measured in five birds from each treatment group during weeks 4 and 5 of the experiment. There were no significant differences between treatments in total feed intake or final body mass. Birds fed the PUFA diets had lower RQ and significantly reduced abdominal fat pad weights (P<0.01) compared with those fed tallow. The dietary lipid profile changes resulted in significantly greater partitioning of energy into lean tissue than into fat tissue (calculated as breast lean tissue weight:abdominal fat mass) in the PUFA groups compared with the saturated fat group (P<0.01; with no difference between the n-3 and n-6 PUFA groups). In addition, the PUFA-rich diets lowered plasma concentrations of serum triacylglycerols and cholesterol. The findings indicate that dietary fatty acid profile influences nutrient partitioning in broiler chickens.     

Fatty acid consumption pattern of Americans: 1987–1988 USDA Nationwide Food Consumption Survey

This study characterized the fatty acid intake pattern and the contribution of different food groups to the fatty acid intake of Americans using the U.S. Department of Agriculture's 1987–1988 Nationwide Food Consumption Survey. The fatty acid intake was estimated using three-day food consumption data for children age 6–11 and for males and females age 12–19, 20–39 and 40 and older. Palmitic acid was the predominant saturated fatty acid (SFA) in the diet for all age sex groups, contributing 52–57% of SFA intake. Oleic acid was the primary monounsaturated fatty acid (MUFA) for all age sex groups, comprising 91–95% of MUFA intake. Linoleic acid was the principle polyunsaturated fatty acid (PUFA) for all age sex groups, contributing 87–92% of PUFA intake. The Milk and Milk Products group was the major contributor of the short chain SFA and lauric and myristic acids. Meat, Poultry and Meat Mixtures were the main sources of palmitic and stearic acids. Grain Products contributed appreciably to the long chain SFA intake. Oleic acid was obtained mainly from Meat, Poultry, Fish and Mixtures. Yeast breads, rolls, cakes, cookies and pastries were the main contributors of linoleic acid intake. A variety of animal and vegetable products contributed to the linolenic acid and C_18:4+20:4 intake, while fish and shellfish were the main sources of C_20:5+22:6 fatty acids. The contribution of the various food groups to intake of individual fatty acids was similar for both males and females. The results of the present study indicate that a wide variety of food groups contribute to the total fat intake Americans.     

Comparison of measures of fatty acid intake by subcutaneous fat aspirate, food frequency questionnaire, and diet records in a free-living population of US men.

In 1986-1987, the authors assessed the fatty acid intake of 118 Boston-area men, aged 40-75 years, by a semiquantitative food frequency questionnaire administered twice, by two 7-day diet records, and by capillary gas chromatography of subcutaneous fat samples obtained by needle aspirate from the lateral buttock. Spearman correlation coefficients between diet record estimates of fatty acid intake (as a percentage of total fat) and fat aspirate measures (as a percentage of total peak area) were as follows: saturated fat, r = 0.16 (p = 0.09); monounsaturated fat, r = 0.22 (p = 0.01); and polyunsaturated fat, r = 0.49 (p = 0.0001). Spearman correlation coefficients between estimates derived from the food frequency questionnaire were as follows: saturated fat, r = 0.18 ( p = 0.05); monounsaturated fat, r = 0.14 (p = 0.14); polyunsaturated fat, r = 0.50 (p = 0.0001); and eicosapentaenoic acid, r = 0.47 (p = 0.0001). These data confirm that the polyunsaturated and eicosapentaenoic fatty acid content of subcutaneous fat is a measure of dietary intake of these fats. Although diet records are commonly thought to be the "gold standard" method of dietary assessment, the similar correlations observed between the fatty acid composition of adipose tissue and estimates of intake from the food frequency questionnaire and from diet records suggest that these two dietary assessment methods have similar validity in the measurement of polyunsaturated fatty acid intake.     

Saturated fats: what dietary intake?

Public health recommendations for the US population in 1977 were to reduce fat intake to as low as 30% of calories to lower the incidence of coronary artery disease. These recommendations resulted in a compositional shift in food materials throughout the agricultural industry, and the fractional content of fats was replaced principally with carbohydrates. Subsequently, high-carbohydrate diets were recognized as contributing to the lipoprotein pattern that characterizes atherogenic dyslipidemia and hypertriacylglycerolemia. The rising incidences of metabolic syndrome and obesity are becoming common themes in the literature. Current recommendations are to keep saturated fatty acid, trans fatty acid, and cholesterol intakes as low as possible while consuming a nutritionally adequate diet. In the face of such recommendations, the agricultural industry is shifting food composition toward lower proportions of all saturated fatty acids. To date, no lower safe limit of specific saturated fatty acid intakes has been identified. This review summarizes research findings and observations on the disparate functions of saturated fatty acids and seeks to bring a more quantitative balance to the debate on dietary saturated fat. Whether a finite quantity of specific dietary saturated fatty acids actually benefits health is not yet known. Because agricultural practices to reduce saturated fat will require a prolonged and concerted effort, and because the world is moving toward more individualized dietary recommendations, should the steps to decrease saturated fatty acids to as low as agriculturally possible not wait until evidence clearly indicates which amounts and types of saturated fatty acids are optimal?     

Fifteen-year time trends in energy and macronutrient intake in German children and adolescents: results of the DONALD study

The DONALD study (Dortmund Nutritional and Anthropometric Longitudinally Designed study) gives the opportunity to evaluate long-term food and nutrient intake data on the basis of 3 d weighed dietary records of infants, children and adolescents since 1985. In this paper, we examine changes in energy and macronutrient intakes (protein, fat, saturated, mono- and polyunsaturated fatty acids, carbohydrates and added sugars) of 795 2-18-year-old subjects between 1985 and 2000 (4483 records). No significant changes in intakes of energy and of protein, polyunsaturated fatty acids and added sugars (as % energy intake, E %) were found. Fat intake decreased significantly in all age groups (between -0.20 and -0.26 E %/year), as well as intake of saturated fatty acids (between -0.11 and -0.14 E %/year) and monounsaturated fatty acids (between -0.07 and -0.014 E %/year). This decline was compensated for by a significant increase in carbohydrate intake (between +0.18 and +0.27 E %/year). The changes in macronutrient intake were mainly due to a decreased consumption of fats-oils (between -0.29 and -1.26 g/year) and meat-fish-eggs (between -0.21 and -2.92 g/year), whereas consumption of bread-cereals (between +0.12 and +2.42 g/year) and potatoes-pasta-rice (between +0.15 and +2.26 g/year) increased slightly. However, since recommended fat intake and fatty acid composition was not reached at the end of the study period by far, further efforts will be necessary to improve macronutrient composition and to stabilize favourable dietary habits.     

Dietary fat intake and risk of type 2 diabetes in women

BACKGROUND: The long-term relations between specific types of dietary fat and risk of type 2 diabetes remain unclear. OBJECTIVE: Our objective was to examine the relations between dietary fat intakes and the risk of type 2 diabetes. DESIGN: We prospectively followed 84204 women aged 34-59 y with no diabetes, cardiovascular disease, or cancer in 1980. Detailed dietary information was assessed at baseline and updated in 1984, 1986, and 1990 by using validated questionnaires. Relative risks of type 2 diabetes were obtained from pooled logistic models adjusted for nondietary and dietary covariates. RESULTS: During 14 y of follow-up, 2507 incident cases of type 2 diabetes were documented. Total fat intake, compared with equivalent energy intake from carbohydrates, was not associated with risk of type 2 diabetes; for a 5% increase in total energy from fat, the relative risk (RR) was 0.98 (95% CI: 0.94, 1.02). Intakes of saturated or monounsaturated fatty acids were also not significantly associated with the risk of diabetes. However, for a 5% increase in energy from polyunsaturated fat, the RR was 0.63 (0.53, 0.76; P < 0.0001) and for a 2% increase in energy from trans fatty acids the RR was 1.39 (1.15, 1.67; P = 0.0006). We estimated that replacing 2% of energy from trans fatty acids isoenergetically with polyunsaturated fat would lead to a 40% lower risk (RR: 0.60; 95% CI: 0.48, 0.75). CONCLUSIONS: These data suggest that total fat and saturated and monounsaturated fatty acid intakes are not associated with risk of type 2 diabetes in women, but that trans fatty acids increase and polyunsaturated fatty acids reduce risk. Substituting nonhydrogenated polyunsaturated fatty acids for trans fatty acids would likely reduce the risk of type 2 diabetes substantially.     

Effect of dietary fatty acid composition on substrate utilization and body weight maintenance in humans

Background/purpose

Dietary fat content is a primary factor associated with the increase in global obesity rates. There is a delay in achieving fat balance following exposure to a high-fat (HF) diet (≥ 40 % of total energy from fat) and fat balance is closely linked to energy balance. Exercise has been shown to improve this rate of adaptation to a HF diet. Recently, however, the role of dietary fatty acid composition on energy and macronutrient balance has come into question.

Methods

We chose studies that compared monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), and saturated fatty acids (SFA). We have reviewed studies that measured diet-induced thermogenesis (DIT), energy expenditure (EE), or fat oxidation (FOx) in response to a HF meal challenge, or long-term dietary intervention comparing these fatty acids.

Results

While single-meal studies show that SFA induce lower DIT and FOx compared to unsaturated fats, the effect of the degree of unsaturation (MUFA vs. PUFA) appears to yet be determined. Long-term dietary interventions also support the notion that unsaturated fats induce greater EE, DIT, and/or FOx versus SFA and that a high MUFA diet induces more weight loss compared to a high SFA diet. Sex and BMI status also affect the metabolic responses to different fatty acids; however, more research in these areas is warranted.

Conclusion

SFA are likely more obesigenic than MUFA, and PUFA. The unsaturated fats appear to be more metabolically beneficial, specifically MUFA ≥ PUFA > SFA, as evidenced by the higher DIT and FOx following HF meals or diets.