Tolerable upper intake levels for trans fat, saturated fat, and cholesterol

Transcription

1 Special Article Tolerable upper intake levels for trans fat, saturated fat, and cholesterol Paula R Trumbo and Tomoko Shimakawa Tolerable upper intake levels (ULs) set by the Institute of Medicine (IOM) are important, in part because they are used for estimating the percentage of the population at potential risk of adverse effects from excessive nutrient intake. The IOM did not set ULs for trans fat, saturated fat, and cholesterol because any intake level above 0% of energy increased LDL cholesterol concentration and these three food components are unavoidable in ordinary diets. The purpose of the analysis presented in this review was to evaluate clinical trial and prospective observational data that were not previously considered for setting a UL with the aim of determining whether the current UL model could be used for saturated fat, trans fat, and cholesterol. The results of this analysis confirm the limitations of the risk assessment model for setting ULs because of its inability to identify a UL for food components, such as cholesterol, that lack an intake threshold associated with increased chronic disease risk.nure_ International Life Sciences Institute INTRODUCTION The 1989 National Research Council Diet and Health report 1 evaluated the clinical (i.e., human feeding studies) and observational evidence for saturated fatty acid (saturated fat) intakes and recommended it should account for no more than 10% of total energy intake. The clinical evidence was based on the effect of saturated fat intakes on blood total and low-density lipoprotein (LDL) cholesterol levels. The report noted that the evidence for the association between high-density lipoprotein (HDL) cholesterol levels and risk of coronary heart disease (CHD) was not firm and therefore unclear. The Diet and Health report 1 stated that the recommendation was based on evidence showing that populations with mean saturated fat intakes of less than 10% of energy had low mean serum total cholesterol levels and were relatively free of atherosclerotic diseases. 2 Thus, clinical data were used to establish a causal relationship between saturated fat intake and CHD risk and observational data were used to identify an intake level that should not be exceeded. The Diet and Health report concluded that clinical studies indicatedtrans fatty acids (trans fat) and their cis isomers had similar effects on plasma lipids. Since prospective observational studies on trans fat were not available at that time, an intake level of trans fat that should not be exceeded was not provided. The recommendation that no more than 300 mg/day of cholesterol be consumed was based on the observation that, within the usual range of intakes ( mg/day, or about mg/ 1,000 kcal), dietary cholesterol influences the plasma cholesterol concentration, primarily LDL cholesterol. As part of the evaluation process for setting Dietary Reference Intakes (DRIs) for macronutrients, the IOM reviewed the evidence for various risk biomarkers of CHD when evaluating the various categories of lipids. 3 No DRIs, including ULs, were set for saturated fat, trans fat, and cholesterol because setting a UL required a threshold intake level for the adverse endpoint. For saturated fat, trans fat, and cholesterol, any intake level above Affiliation: PR Trumbo and T Shimakawa are with the Office of Nutrition, Labeling and Dietary Supplements, U.S. Food and Drug Administration, College Park, Maryland, USA. Correspondence: PR Trumbo, HFS-830, 5100 Paint Branch Parkway, College Park, MD 20740, USA. paula.trumbo@fda.hhs.gov, Phone: , Fax: Key words: cholesterol, saturated fatty acid, tolerable upper intake levels, trans fatty acids 270 doi: /j x

2 0% of energy increased LDL cholesterol concentration and therefore increased risk of CHD. Because saturated fat, trans fat, and cholesterol are unavoidable in ordinary diets, it was recommended that intakes of each be as low as possible while consuming a nutritionally adequate diet. 3 Since the release of the DRI report on macronutrients, there have been discussions about how to improve the process for establishing ULs for nutrients. 4,5 In the 2010 report of the Dietary Guidelines for Americans Committee, 6 the Committee concluded there is strong evidence, dating back to 2004, for a positive association between saturated fat intake and risk of CHD. They recommended that less than 10% of energy be consumed in the form of saturated fat and noted that further benefits could be gained by reducing saturated fat intake over time to 7% of energy, while substituting with polyunsaturated and monounsaturated fat sources. This recommendation was based, in part, on data from prospective cohort studies. 7,8 Analysis of a 14-year follow-up in the Nurses Health Study concluded that the replacement of 5% energy from saturated fat with energy from unsaturated fats would reduce the risk of CHD by 42%. 7 A significant reduction (13%) in CHD risk with a 5% replacement of saturated fat was also reported by Jakobsen et al. 8 based on 11 cohorts. The Committee also noted there are benefits of limiting trans fat intake from industrial sources; however, it was recommended to not limit trans fats occurring naturally in foods such as red meat and dairy products. The 2010 Dietary Guidelines Committee upheld prevailing recommendations that cholesterol intake should be limited to less than 300 mg/day and suggested that further reductions to less than 200 mg/day be recommended for individuals at high risk for cardiovascular disease and type 2 diabetes. In a 1993 final rule, implementing the Nutrition Labeling and Education Act of 1990, the United States Food and Drug Administration (FDA) established nutrition reference values for use in nutrition labeling. 9 Currently, there are two sets of label reference values: Reference Daily Intakes and Daily Reference Values (DRVs). The FDA based its Reference Daily Intake for vitamins and minerals on Recommended Dietary Allowances and Estimated Safe and Adequate Daily Intakes established by the National Academy of Sciences. The FDA based its DRVs on recommendations in the Diet and Health Report, 1 the Surgeon General s Report on Nutrition and Health, 10 and the 1990 Dietary Guidelines for Americans. 11 The FDA uses Reference Daily Intakes and DRVs as Daily Values (DV) in the Nutrition Facts label on food products and as qualifying criteria for food products to bear certain nutrient content claims and health claims. The DRVs are specific for protein, fat, and carbohydrate and for nutrients associated with the risk of chronic diseases or health-related conditions; such food components include saturated fat (for CHD), cholesterol (for CHD), fiber (for cancer and CHD), sodium (for blood pressure), and potassium (for blood pressure and stroke). 11 The current DRVs for saturated fat and cholesterol are 20 g (10% of 2,000 calories) and 300 mg/day. Because an intake level of trans fat that should not be exceeded has not been recommended by Federal agencies in the United States, such as in the Dietary Guidelines for Americans, or by the IOM, there currently is no DRV, and therefore no DV for trans fat. While observational evidence was reviewed by the IOM s DRI panel, it was not considered in setting a UL for trans fat, saturated fat, and cholesterol. 3 Provided that causality has been established, observational evidence can identify thresholds of intake at which the risk of chronic disease, such as CHD, is significantly increased. The objective of the current analysis was to evaluate additional evidence for potential use in setting a UL for trans fat, saturated fat, and cholesterol. Furthermore, the association between saturated fat and trans fat intake and CHD risk was compared for evaluating the appropriateness of potential ULs for each fatty acid. IDENTIFICATION AND ANALYSIS OF STUDIES This analysis was based on randomized clinical and prospective cohort observational studies published since No randomized clinical studies were identified that directly evaluated the effect of trans and saturated fat intake on CHD events (myocardial infarction or sudden death). This evaluation included clinical studies that measured risk biomarkers, used a crossover design, and were conducted for a minimum of 3 weeks for each clinical diet. While a number of risk biomarkers for CHD have been measured in clinical trials, only surrogate risk biomarkers (i.e., risk biomarkers that substitute for a clinical endpoint) of CHD risk (i.e., total and LDL cholesterol) were included in this evaluation. While LDL cholesterol is not the only contributor to CHD, biological plausibility has been established between LDL cholesterol levels and CHD risk. 12,13 The independent effect of HDL cholesterol has been shown in animal models; however, it has been difficult to differentiate the independent effects of increasing HDL cholesterol levels on reduction of CHD risk in clinical studies. 12 A recent IOM report on the evaluation of biomarkers and surrogate endpoints in chronic disease concluded that the data were limited and the biological role of HDL in heart disease risk was not fully understood. 13 The evidence for other CHD risk biomarkers is equally or even more uncertain. For analysis of the relationship between saturated versus trans fat intake and blood LDL or total cholesterol 271

3 levels, the clinical diets within each study were required to be similar in energy and in the level (percent of energy) of fat, carbohydrate, protein, polyunsaturated fat, saturated or trans fat, and in the level of cholesterol and dietary fiber. Some studies did not provide information on dietary fiber, but studies that provided all meals as rotating diets during each intervention were included. For analysis of the trans : saturated fat ratio, the clinical studies met the above dietary criteria; however, the trans and saturated fat content between the control and experimental diets could vary. Clinical studies were required to provide a statistical analysis of the various experimental diets. Regression analysis was conducted using the changes in trans and saturated fat intakes compared to the control period as the independent variable and changes in LDL or total cholesterol concentrations compared to the control period as the dependent variable. Prospective cohorts were identified from which scientific conclusions could be drawn about an association between trans fat, saturatedfat, andcholesterolintakeand the risk of CHD. Intake of foods containing these fats was estimated using a validated food frequency questionnaire. The studies included in the analysis adjusted for the majority of risk factors of heart disease including age, smoking, body mass index, alcohol use, blood pressure/ hypertension status, physical activity, energy intake, polyunsaturated fat/linoleic acid intake, saturated fat intake, cholesterol intake, and fiber intake. Trans fat FINDINGS FOR TRANS FAT, SATURATED FAT, AND CHOLESTEROL To ascertain whether a potential UL could be identified, the relationship between the change in total and LDL cholesterol and percent of energy intake from trans fat was evaluated based on nine clinical trials that met the criteria discussed above Two of these studies had two test periods with different trans fat intake levels, and these results were consequently treated as separate data points. Regression coefficients for the relationship between the change in LDL cholesterol and percent of energy intake from trans fat were not significant (P > 0.05), and the analysis did not show a threshold intake level at which LDL cholesterol concentration increased (Figure 1). The finding was similar for total cholesterol (change in total cholesterol levels = change in trans fatty acid intakes [R 2 = 0.23; P = 0.137]). While this specific type of analysis was not conducted by the IOM for determining a UL for trans fat, Figure 1 supports the IOM s conclusion that any intake level of trans fat above 0% of energy increased LDL cholesterol concentration. 3 A threshold is particularly important when the nutrient is not essential, like trans fat, and information about an intake level to meet an individual s daily requirement (i.e., a recommended dietary allowance) is consequently lacking. Thus, due to the lack of a Change in LDL Cholesterol Levels (mmol/l) Change in Trans Fatty Acid Intakes (% Energy) Figure 1 Change in LDL cholesterol levels by change in trans fatty acid intakes. The total number of crossover studies was nine, including two studies with two data points. Change in LDL cholesterol levels = change in trans fatty acid intakes. R 2 = 0.35; P =

4 threshold between trans fat intake and LDL cholesterol, a UL for trans fat could not be identified based on data from clinical trials that measure LDL cholesterol. While observational studies were reviewed in the DRI report on macronutrients, such evidence was not considered in setting a UL for trans fat, saturated fat, or cholesterol. 3 For establishing a UL, observational data were considered for a few nutrients, such as iron and vitamin A. The UL for vitamin A for women of reproductive age was based on observational studies that evaluated the relationship between vitamin A intake and teratogenic effects, specifically neural crest defects. 23 The specific study that was used to identify a no-observed-adverseeffect-level (NOAEL) for vitamin A reported a significantly increased risk of birth defects at the cranial neural crest sites among women who consumed more than 4,500 mg/day of preformed vitamin A. 24 Upon identifying a NOAEL of <4,500 mg/day, a UL of 3,000 mg/day was set for vitamin A based on an uncertainty factor of 1.5.While there are limitations in estimating nutrient intake based on dietary assessment methods and confounders of disease risk, information on inter-individual variability could be considered when determining an uncertainty factor. Using the approach taken for vitamin A, Table 1 was constructed to show the prospective observational studies that evaluated the relationship between trans fat intake andriskofchd All follow-up reports of each cohort were included since a broader range of trans fat intake was observed during earlier reports, especially at the earliest follow-up period. The Health Professional s Study reported a significant increase in the risk of death due to CHD at the second quintile of intake; however, increased risk was not observed for the higher quintiles of intake, as reflected in the P value for trend (0.42). 25 An increased risk of nonfatal myocardial infarction and CHD death was observed at the third quintile of intake during the 20-year follow-up of the Nurses Health Study 29 ; however, increased risk was not observed at the fourth quintile of intake, nor during the 8- and 14-year follow-up periods. 27,28 Increased risk of CHD was observed at the highest quintiles of intake during the 14- and 20-year follow-up periods of the Nurses Health Study and with trans fat intakes of 2.8% and 2.9% of energy. 28,29 The Finnish ATBC Study reported an increased risk of coronary death at the highest quintile of trans fat intake (5.6 g/day). 30 The Zutphen Elderly Study observed an increased risk of CHD at the highest tertile of trans fat intake (>4.86% of energy). 31 Using an approach similar to that for vitamin A, it may be possible to identify a NOAEL or a lowestobserved-adverse-effect-level by identifying an intake level below or at the lowest percentile of intake at which increased risk was found. Saturated fat A number of reports have collectively analyzed the available clinical studies on the effect of saturated fat intake on total and LDL cholesterol levels. 32,33 Similar to trans fat intake, the relationship is linear such that total and LDL cholesterol levels increase with any intake level above zero. 3 These reports, however, included studies that did not consider trans fat intake in the criteria for including studies or reported the effect of the individual fatty acids when substituting for carbohydrate. For the purposes of the present article, an insufficient number of studies were identified for conducting a regression analysis in which the diet composition of all of the relevant macronutrients, including trans fat, were controlled for and reported, and the various experimental diets collectively yielded a broad range of intake levels for saturated fat. Since the publication of the Diet and Health report 1 in 1989, several well-designed prospective cohort studies have been published that have evaluated saturated fat intake and cardiovascular disease risk (Table 2) Despite the findings that saturated fat intake increases LDL and total cholesterol levels in a dose-response manner in clinical studies, these prospective cohorts have generally not found a significant association between saturated fat intake and CHD risk at the range of intake levels consumed. Table 2 shows that only the Health Professional s Study observed a significant increased risk (RR = 1.72) of CHD death at the highest quintile of saturated fat intake (14.8% of energy). 25 Similar to the findings for vitamin A, a number of observational studies showed no adverse effects at lower levels of saturated fat intake. Trans fat versus saturated fat In considering whether potential ULs for trans and saturated fat would make sense in terms of their relative effect on CHD risk, the relationship between the change in the relative intake of trans and saturated fat and total and LDL cholesterol concentration was evaluated. Thirteen studies were identified that met the criteria for this evaluation ,34 37 Figure 2 shows the relationship between the change in the trans : saturated fat ratio and LDL cholesterol concentration up to 1.2. Increasing the ratio by 0.1 (e.g., 1% trans fat : 10% saturated fat to 2% trans fat : 10% saturated fat) was associated with an increase in LDL cholesterol of mmol/l (R 2 = 0.20; P = 0.080). Increasing the ratio by 0.1 increased total cholesterol by mmol/l (R 2 = 0.03; P = 0.558). Similar to these findings, a meta-analysis of 13 clinical studies, most of which were included in the above analysis, showed there was no statistically significant change in total (0.006 mmol/l) or LDL ( mmol/l) cholesterol 273

5 Table 1 Prospective observational studies on trans fat intake and risk of coronary heart disease and death. Study Endpoint; no. of cases Relative risk at quintiles (Q) of trans fat intake* Q1 Q2 Q3 Q4 Q5 Health Professional s Study Men 6-year follow-up 25 Total MI; 1.5 g/d 2.2 g/d; 2.7 g/d; 3.3 g/d; 4.3 g/d; 505 cases 1.12 ( ) 1.12 ( ) 1.12 ( ) 1.21 ( ) CHD death; 1.5 g/d 2.2 g/d; 2.7 g/d; 3.3 g/d; 4.3 g/d; 229 cases 1.63 ( ) 1.18 ( ) 1.59 ( ) 1.41 ( ) 14-year follow-up 26 Ischemic stroke; 1.67 g/d 2.34; 2.86; 3.44; 4.42; 455 cases 0.96 ( g/day) 0.80 ( g/day) 0.90 ( g/day) 0.80 ( g/day) Nurses Health Study Nonfatal MI and CHD death; 2.4% 3.2%; 3.9%; 4.5%; 5.7%; Women 8-year follow-up cases 1.12 ( ) 0.99 ( ) 1.16 ( ) 1.47 ( ) 14-year follow-up 28 Nonfatal MI and CHD death; 1.3% 1.7%; 2.0%; 2.4%; 2.9%; 939 cases 1.09 ( ) 1.16 ( ) 1.24 ( ) 1.53 ( ) 20-year follow-up 29 Nonfatal MI and CHD death; 1.3% (2.4 g/d) 1.6%; 1.9%; 2.2%; 2.8%; (5.5 g/d) 1,766 cases 1.08 ( ) 1.29 ( ) 1.19 ( ) 1.33 ( ) Coronary death; 1.3 g 1.7 g; 2.0 g; 2.7 g; 5.6 g; 635 cases 1.05 ( g/day) 1.12 ( g/day) 0.9 ( g/day) 1.39 ( g/day) Nonfatal MI; 1.3 g 1.7 g; 2.0 g; 2.7 g; 6.2 g; 1,399 cases 1.10 ( g/day) 0.97 ( g/day) 1.07 ( g/day) 1.14 ( g/day) Finnish ATBC Study Male smokers 6-year follow-up 30 Zutphen Elderly Study 31 Elderly men 10-year follow-up Nonfatal MI and CHD death; <3.11% % ; >4.86% ; 98 cases 1.34 ( ) 2.0 ( ) * Intake of trans fat per quintile of intake as g/day or % of energy; relative risk (95% confidence interval). Tertiles of intake. Abbreviations: CHD, coronary heart disease; MI, myocardial infarction, Q, quintile. 274

6 Table 2 Prospective observational studies on saturated fat intake and risk of coronary heart disease and death. Study Endpoint; no. of cases Relative risk at quintiles (Q) of saturated fat intake* Q1 Q2 Q3 Q4 Q5 Health Professional s Study Men 6-year follow-up 25 Nonfatal MI; 7.2% 9.5%; 10.9%; 12.3%; 14.8%; 505 cases 1.01 ( ) 0.84 ( ) 0.90 ( ) 0.96 ( ) CHD death; 9.5%; 10.9%; 12.3%; 14.8%; 229 cases 1.41 ( ) 1.38 ( ) 1.32 ( ) 1.72 ( ) 14-year follow-up 26 Ischemic stroke; 17 g/d 21 g/day; 24 g/day; 26 g/day; 31 g/day; 455 cases 1.24 ( ) 1.26 ( ) 1.13 ( ) 1.21 ( ) Nurses Health Study Women 14-year follow-up 28 Nonfatal MI and CHD death; 10.7% 12.8%; 14.3%; 16.0%; 18.8%; 939 cases 0.87 ( ) 0.85 ( ) 1.05 ( ) 0.95 ( ) 20-year follow-up 29 Nonfatal MI and CHD death; 10.1% 11.9%; 13.3%; 14.8%; 17.6%; 1,766 cases 0.94 ( ) 0.96 ( ) 1.01 ( ) 0.97 ( ) Finnish ATBC Study Male smokers 6-year follow-up 30 Coronary death; 11% (34.7 g) 43.3 g/day; 50.3 g/day; 57.4 g/day; 21.9%; (67.5) 635 cases 0.8 ( ) 0.77 ( ) 0.83 ( ) 0.73 ( ) Nonfatal MI; 43.3 g; 50.3 g; 57.4 g; 21.0% (67.5 g); 1,399 cases 11% (34.7 g) 0.87 ( ) 0.82 ( ) 0.95 ( ) 0.87 ( ) Malmö Diet and Cancer Study Coronary events; 908 (women/men) 12.2%/12.3% 15.2%/15.3% 17.5%/17.7% 21.8%/22.3% Men and women 40 Women 0.99 ( ) 0.77 ( ) 0.98 ( ) Men 1.02 ( ) 1.01 ( ) 1.05 ( ) Quartiles of intake. * Intake of saturated fat per quintile of intake as g/day or % of energy; relative risk (95% confidence interval). Abbreviations: CHD, coronary heart disease; MI, myocardial infarction; NR, not reported; Q, quintile. 275

7 Change in LDL Cholesterol Levels (mmol/l) Change in the Trans Fatty Acid Intake to Saturated Fatty Acid Intake Ratios Figure 2 Change in LDL cholesterol levels by change in the trans fatty acid intake to saturated fatty acid intake ratios. The total number of crossover studies was 12 including three studies with two data points. Change in LDL cholesterol levels = change in the trans fatty acid intake to saturated fatty acid intake ratios. R 2 = 0.20; P = concentration with each 1% energy replacement of trans fat with saturated fat. 38 Furthermore, Kris-Etherton et al. 39 reported that with every 1% of energy increase from trans fat, the increase in plasma cholesterol was not greater than the increase observed for the individual saturated fats, lauric acid, myristic acid, and palmitic acid. While the evidence from prospective cohort studies for a positive association between saturated fat and CHD risk was very limited (Table 2), the association between trans fat and CHD risk was more evident (Table 1). A meta-analysis was conducted on these prospective cohort studies that evaluated the relationship between saturated and trans fat intake and risk of CHD. 38 This metaanalysis showed that each 2% energy replacement of trans fat with saturated fat would significantly lower CHD risk by 17%. It is difficult to comment, however, on the relative effects of these fatty acids since the range of intake levels was very different (trans fat, %; saturated fat, 7 22%). Based on the available evidence, which unfortunately lacks clinical studies on the effect of trans and saturated fat on coronary events, the findings from clinical studies using surrogate markers of CHD risk and observational studies are inconsistent and thus prevent a conclusion from being made about whether one fatty acid is more adverse than the other. While recognizing that the levels of trans and saturated fats present in foods differ greatly, this comparative information would not be helpful in evaluating potential ULs for each fatty acid. Cholesterol Similar to the findings for saturated fat, a number of studies have demonstrated a linear dose-response relationship between cholesterol intake and LDL and total cholesterol concentrations. 3 Therefore, this information was not suitable for establishing a UL for cholesterol. Also similar to saturated fat, an insufficient number of studies were identified for conducting a regression analysis in which the diet composition of all of the relevant macronutrients, including trans fat, were controlled for and reported, and the various experimental diets collectively yielded a broad range of intake levels for cholesterol. Table 3 shows the prospective cohort studies that reported on the relationship between cholesterol intake and risk of CHD. As can be seen, none of these studies observed an increased risk of CHD or CHD-related mortality at the highest quintile intake levels of as high as 768 mg/day. 30 Therefore, the observational evidence does not provide a threshold intake level for dietary cholesterol and CHD risk. CONCLUSION While there is sufficient clinical evidence to support a causal association between saturated fat, trans fat, and cholesterol intake and surrogate endpoints of CHD risk, a UL was not set by the IOM because a threshold intake 276

8 Table 3 Prospective observational studies on cholesterol intake and risk of coronary heart disease and death. Study Endpoint; no. of cases Relative risk at quintiles of cholesterol intake (mg/day)* Q1 Q2 Q3 Q4 Q5 Health Professional s Study Men 6-year follow-up 25 Nonfatal MI; ; 290; 338; 442; 505 cases 0.86 ( ) 0.98 ( ) 0.94 ( ) 1.03 ( ) CHD death; 246; 290; 338; 442; 229 cases 0.92 ( ) 1.18 ( ) 1.11 ( ) 1.25 ( ) 14-year follow-up 26 Ischemic stroke; ; 278; 321; 398; 455 cases 0.93 ( ) 0.80 ( ) 0.76 ( ) 0.93 ( ) Nurses Health Study Women 14-year follow-up 28 Nonfatal MI and CHD death; ; 188; 217; 273; 939 cases 1.15 ( ) 1.08 ( ) 1.24 ( ) 1.17 ( ) Coronary death; ; 543; 621; 768; 635 cases 0.9 ( ) 0.81 ( ) 0.86 ( ) 0.92 ( ) Nonfatal MI; 390 g 477; 543; 621; 768; Finnish ATBC Study Male smokers 6-year follow-up 30 1,399 cases 0.86 ( ) 0.91 ( ) 0.87 ( ) 0.93 ( ) * Intake of cholesterol per quintile of intake as mg/day; relative risk (95% confidence interval). Abbreviations: CHD, coronary heart disease; MI, myocardial infarction; Q, quintile. level above which CHD risk increases could not be identified. The possibility of utilizing observational evidence for identifying a UL based on a NOAEL was considered, recognizing the limitations of dietary assessment methods and confounders of disease risk. While a threshold intake level could be identified for trans and saturated fat, such a level could not be identified for cholesterol. The results of this analysis confirm the limitations of the risk assessment model for setting ULs because of its inability to identify a UL for food components, such as cholesterol, that lack an intake threshold associated with increased chronic disease risk. Acknowledgment Declaration of interest. The authors have no relevant interests to declare. REFERENCES 1. National Research Council. Diet and Health: Implications for Reducing Chronic Disease Risk. Washington, DC: National Research Council/National Academy Press; Available at: Accessed 9 April Keys A. Seven Countries: A Multivariate Analysis of Death and Coronary Heart Disease. Cambridge: Harvard University Press; Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate. Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, DC: Institute of Medicine of the National Academies/National Academy Press; Available at: catalog.php?record_id=10490#toc. Accessed 9 April Institute of Medicine. The Development of DRIs : Lessons Learned and New Challenges. Washington, DC: Institute of Medicine of the National Academies/National Academy Press; Available at: catalog.php?record_id=12086#toc. Accessed 9 April World Health Organization/Food and Agriculture Organization of the United Nations. A Model for Establishing Upper Levels of Intake for Nutrients and Related Substances. Geneva: World Health Organization; U.S. Department of Agriculture and U.S. Department of Health and Human Services. Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans Available at: DGACReport.htm. Accessed 23 March Hu FB, Manson JE, Willett WC. Types of fat and risk of coronary heart disease: a critical review. J Am Coll Med. 2001;20: Jakobsen M, O Reilly EJ, Heitmann BL, et al. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. Am J Clin Nutr. 2009;89: U.S. Food and Drug Administration. Food labeling; reference daily intakes and daily reference values. Final rule. Fed Regist. 1993;58: U.S. Department of Health and Human Services. The Surgeon General's Report on Nutrition and Health. Washington, DC; Available at Accessed 23 March

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