So Many Nutrition Recommendations—Contradictory or Compatible?

The DRI, NCEP, and ADA guidelines give ranges for the percentage of total daily energy from dietary fat, whereas the AHA simply recommends a fat intake of ≤30% of total energy to assist in limiting consumption of total energy as well as saturated fat.

The DRI report concludes that adults should consume 20–35% of total energy intake from fat; infants and younger children generally need a somewhat higher proportion of fat in their diets than do adults.

The NCEP recommendation for total fat is in the range of 25–35% of energy intake provided that saturated fats and trans fatty acids are kept low. It notes that a higher intake of total dietary fat, mostly in the form of unsaturated fat, can help reduce triglycerides and raise HDL cholesterol in people with the metabolic syndrome.

The ADA also could not find evidence to support a guideline with a specific percentage of total energy from dietary fat. Based on expert consensus, it concludes that fat intake should be individualized, with carbohydrate and monounsaturated fat together providing 60–70% of energy intake. It clarifies that, when determining the monounsaturated fat content of the diet, the individual’s metabolic profile and need for weight loss should be considered. It cautions that increasing fat intake may result in increased energy intake. Furthermore, ethnic or cultural preferences may play a role in determining whether saturated fat is to be replaced with carbohydrate or monounsaturated fat.

The DRI report recommends that intake of saturated fatty acids and trans fatty acids be kept as low as possible while consuming a nutritionally adequate diet because many of the foods containing these fats also provide valuable nutrients. It notes that a nutritionally adequate diet is possible with only 5% of total energy from saturated fats.

The DRI report points out that neither saturated nor trans fatty acids have a known beneficial role in preventing chronic disease, and neither are required at any level in the diet. Both increase the risk of heart disease in some people by raising the levels of LDL cholesterol in the bloodstream, and this occurs even with very small quantities in the diet. Furthermore, recent data have demonstrated that the higher the intake of trans fatty acids, the higher the ratio of LDL to HDL cholesterol and that the magnitude of this effect may be greater for trans fatty acids than for saturated fats.

Although not in the report, it is helpful to remember that only ∼3% of usual total energy is from trans fatty acids compared to ∼11% from saturated fats. Because saturated fats are consumed in larger amounts, lowering saturated fats is likely to have a greater overall beneficial effect.

All three of the health organizations have similar guidelines for the desirable percentages of energy from saturated fat and for minimizing intake of trans fats (Table 3). The ADA notes that research supporting these guidelines is from the general population; studies in people with diabetes demonstrating the effects of specific percentages of saturated fatty acids (e.g., 10 vs. 7% of energy) and the effect of trans fats are not available in the scientific literature.

The maximal effect of nutrition therapy is typically reported to reduce LDL cholesterol by 15–25 mg/dl.8 Thus, if LDL cholesterol exceeds the goal by >25 mg/dl, pharmacological therapy is generally needed in combination with lifestyle strategies. The target LDL cholesterol level for adult patients with diabetes is <100 mg/dl.9 In patients treated with only nutrition therapy, lipids should be evaluated at 6-week intervals, with consideration of pharmacological therapy between 3 and 6 months. Pharmacological treatment is indicated if there is an inadequate response to lifestyle modifications and improved glucose control.

A meta-analysis of 37 dietary intervention studies in free-living subjects indicated that lowering saturated fat to 7–10% of total energy and dietary cholesterol intake to 200–300 mg/day decreases total cholesterol by 24–32 mg/dl (10–13%), LDL cholesterol by 19–25 mg/dl (12–16%), and triglycerides by 15 mg/dl (8%).10 HDL cholesterol decreased by 7% in only the more restrictive approach. Adding exercise resulted in greater decreases in total and LDL cholesterol and triglycerides and prevented the decrease in HDL cholesterol associated with the lower-fat diet.

Although generally referred to simply as monounsaturated fatty acids (MUFAs), it should be noted the guidelines are for the cis form of MUFAs. (In natural unsaturated fatty acids, the two carbons participating in a double bond each bind a hydrogen on the same side of the bond and thus are the cis-isomer form. Hydrogenation of unsaturated fatty acids adds hydrogen to liquid oils to form a solid and stable fat, and in the process, fatty acids are reshaped into trans fatty acids.)

Monounsaturated and polyunsaturated fatty acids reduce blood cholesterol concentrations when they replace saturated fatty acids in the diet. People must get two types of polyunsaturated fatty acids, linoleic acid (an omega-6 fatty acid) and α-linolenic acid (an omega-3 fatty acid), from the foods they eat because the body cannot make them. A lack of either one will result in symptoms of deficiency, including scaly skin, dermatitis, and reduced growth. However, this is rare in the United States and Canada.

Studies have shown that populations with diets naturally high in α-linolenic acid and longer-chain omega-3 fatty acids (common in countries where large quantities of fatty fish are eaten) have a decreased risk of cardiovascular disease. Additionally, individuals whose diets are naturally high in linoleic acids and longer-chain omega-6 fatty acids (commonly obtained from vegetable oils) have higher levels of HDL cholesterol, which is also protective of cardiovascular disease. Based on the median intakes, the DRI report sets an AI of linoleic acid for adult men and women of 17 and 12 g/day, respectively, and an AI for α-linolenic acid of 1.6 and 1.1 g/day, respectively. Fatty fish, nuts, avocados, olives, flaxseed, soybeans, and various oils, including safflower, canola, and corn oil, are sources of these beneficial fatty acids.

The AHA notes that in the absence of weight loss, diets high in total carbohydrate (e.g., >60% of energy) can lead to elevated triglycerides and reduced HDL cholesterol. These effects do not occur with substitution of monounsaturated or polyunsaturated fats for saturated fat. NCEP suggests monounsaturated fat can be up to 20% of total energy and polyunsaturated fat up to 10% of total energy.

The ADA is more cautious in recommending increased intake of monounsaturated or polyunsaturated fats. Diets high in monounsaturated fat or low in fat and high in carbohydrate result in improvement in glucose tolerance and lipids compared to diets high in saturated fats. Diets enriched with monounsaturated fat may also reduce insulin resistance;11 however, other observational studies have reported total dietary fat (regardless of the type of fat) to be associated with insulin resistance.12–16 

In people with type 2 diabetes and in the absence of weight loss, a diet high in total carbohydrate (e.g., >60% of total energy) leads to an elevation in triglycerides and a lowering of HDL cholesterol. The classic study by Garg et al.17 compared diets high in either carbohydrate (55% of energy intake) or monounsaturated fat (45% total fat, 25% monounsaturated fat) and in which energy intake is maintained so that subjects did not lose weight. LDL cholesterol was lowered equivalently, but on the high-carbohydrate diet, triglycerides were 39 mg/dl higher than on the monounsaturated fat diet, with no differences in fasting glucose, insulin, or hemoglobin A_1c (A1C). In other studies,18,19 when energy intake was reduced and a low-fat, high-carbohydrate diet was compared to a diet high in monounsaturated fat, there was no detrimental effect on triglycerides. Energy intake, therefore, appears to be a factor in determining the effects of high-carbohydrate diets versus diets high in monounsaturated fat on triglycerides and HDL cholesterol.

However, the level of carbohydrate intake is also a factor in that carbohydrate needs to exceed 55–60% of energy in weight-maintaining diets to raise triglycerides. In the United Kingdom Prospective Diabetes Study (UKPDS), after intensive individual nutrition therapy with dietitians emphasizing a low-fat diet, the average carbohydrate intake was 43% and had not increased to the recommended 50–55%. Protein intake was 21%, fat intake was 37%, and males had an estimated mean energy intake of ∼1,800 kcal compared to ∼1,500 kcal for females.20 This intake is similar to that of many patients with type 2 diabetes in the United States, suggesting that the carbohydrate level of a recommended low-fat diet is in actuality unlikely to elevate triglycerides.

The ADA recommends that an individual’s metabolic profile and need to lose weight will determine nutrition therapy recommendations. For people who need to lose weight, a lower-energy intake and a low-fat, moderate-carbohydrate approach can be emphasized. For people who do not need to lose weight, an approach substituting monounsaturated fats for saturated fats may be employed to improve triglycerides or postmeal glycemia (B level evidence).

A diet high in monounsaturated fat selected ad libitum may lead to higher energy intakes and weight gain. The major monounsaturated fat in the diet is oleic, and major dietary sources of oleic are the same as for saturated fat: dairy, beef, pork, poultry, and lamb. This means that when saturated fat is restricted, so is monounsaturated fat. Therefore, to increase monounsaturated fats, individuals need to add nuts and oils to their diets, and unless portion sizes are carefully monitored, it may be easy to increase total energy intake.

In general, research suggests that low-fat diets are usually associated with modest weight loss, which can be maintained as long as the diet is continued.21 With this modest weight loss, decreases in total cholesterol and triglycerides and an increase in HDL cholesterol are observed. Consistent with this, low-fat, high-carbohydrate diets over long periods of time have been shown to not increase triglycerides and reportedly have led to modest weight loss22–24 as well as to maintenance of weight loss better than other types of reduced-energy diets. Conversely, diets high in fat also tend to be higher in energy intake.25–27 Therefore, the ADA concluded that reduced-fat diets when maintained over the long-term contribute to weight loss and improvements in dyslipidemia (B level evidence).

There is evidence from the general population that foods containing n-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), confer cardioprotective effects, and both AHA and ADA suggest that at least two servings of fish per week can be recommended.

The majority of studies in subjects with type 2 diabetes, however, have used n-3 supplements, which lower triglycerides but slightly raise LDL cholesterol.28–30 No detrimental effects on glycemia have been observed, but if supplements are used, the effects on LDL cholesterol should be monitored. n-3 supplements may be most beneficial in the treatment of severe hypertriglyceridemia.31,32 

The DRI report notes that, along with saturated and trans fats, dietary cholesterol has no role in preventing chronic disease and is not required in the diet. Thus, intake should be kept as low as possible.

The AHA found no evidence for cholesterol guidelines for all individuals but recommends <300 mg/day on average for the general public. It notes that by limiting cholesterol intake from foods high in animal fat, the guideline for saturated fat intake also will be met.

The National Cholesterol Education Program (NCEP) therapeutic lifestyle change recommends <200 mg/day.

The ADA recommends that for all people with diabetes, dietary cholesterol should be <300 mg/day. Some individuals (i.e., those with LDL cholesterol >100 mg/day) may benefit from lowering dietary cholesterol to <200 mg/day (A level evidence). Preliminary observational evidence suggests that people with diabetes compared to nondiabetic subjects are more susceptible to risks from dietary cholesterol.33 In people with diabetes, higher intakes of dietary cholesterol were associated with an increased risk of coronary heart disease. Therefore, it may be prudent for people with diabetes to be more conservative in limiting cholesterol-containing foods.

Carbohydrate, which includes sugars and starches, provides energy to the cells of the body, particularly the brain. The DRI report sets the first RDA for total carbohydrate for adults and children at 130 g/day, the minimum amount of carbohydrate needed to produce enough glucose for the brain to function. Most people typically exceed this daily amount, with the median intake of available carbohydrate ranging, depending on age, from ∼200 to 300 g/day for men and 180–230 g/day for women. However, individuals who follow extremely-low-carbohydrate diets may not be getting enough carbohydrate from the food they eat.

Although the acceptable range for carbohydrate is 45–65% of total calories, the DRI suggests that no more than 25% of total calories come from added sugars. This suggested maximum level is based on trends that show that people whose diets are at this level of added sugars or above are more likely to have poorer intakes of important essential nutrients. Although supplements may compensate for poor eating habits, the DRI stresses the benefit of getting needed nutrients from foods. Natural foods are chemically complex and likely to contain other healthy nutrients as yet unknown.

All three organizations support the importance of foods containing carbohydrate, such as whole grains, fruits, vegetables, and low-fat milk, in a healthy diet. However, the ADA concludes that in regard to the glycemic effects of carbohydrate, the total amount of carbohydrate in meals or snacks is more important than the source (starch or sugars) or type (glycemic index) (A level evidence).

Various health benefits, including increased laxation and lower blood glucose and cholesterol concentrations, have been ascribed to fiber in the diet. The DRI report for the first time makes fiber recommendations—men and women 50 years old and younger should have 38 and 25 g/day, respectively, of total fiber. The recommended intakes for men and women over 50 years of age are 30 and 21 g/day, respectively, because of decreased energy consumption among individuals in this age-group. This amount was selected based on the amount that appears to be necessary to lower cardiovascular risk.

Recommendations for fiber vary among the other sets of guidelines. AHA acknowledges that soluble fibers (notably β-glucan and pectin) modestly reduce total cholesterol and LDL cholesterol beyond what is observed from a diet low in saturated fat and cholesterol. However, it notes that there are insufficient data to recommend a specific target for fiber intake. Consumption of the recommended portions of grains, fruits, vegetables, legumes, and nuts can result in an intake of >25 g/day of fiber.

NCEP recommends increasing viscous (soluble) fiber by 10–25 g/day in addition to eating a diet low in saturated fat, trans fat, and cholesterol to enhance lowering of LDL cholesterol.

The ADA questions whether the palatability and gastrointestinal side effects of fiber in the amounts needed to demonstrate favorable effects would be acceptable to most people over the long term. It is of interest to review fiber intake in the UKPDS.20 In that study, it was recommended that half of the energy content from the diet be obtained from unrefined carbohydrate; this resulted in a mean fiber intake of 22 g/day, which was less than the recommended 30 g/day. In support of fiber, a study comparing a diet that included 24 g/day to a diet containing 50 g/day of fiber reported improved glycemic control, reduced hyperinsulinemia, and decreased plasma lipids from 50 g/day and no beneficial effects from 24 g/day of fiber.34 Based on results from this and other studies,35–37 it appears that large amounts of fiber are necessary to observe benefits. Therefore, the ADA concluded that although, just as for the general public, fiber intake is to be encouraged for its other health benefits, there is no reason for people with diabetes to consume more fiber than do other Americans (B level evidence).

Evidence for the cholesterol-lowering effects of dietary fiber comes from a meta-analysis of 67 controlled trials in which the authors concluded that the effect of soluble fiber on total and LDL cholesterol, within the range of practical intake, is small.38 For example, daily intake of 3 g of soluble fiber from oats (three servings of oatmeal, 28 g each, or three apples) can decrease total cholesterol by ∼5 mg/dl, a reduction of ∼2%. Therefore, the additional contribution of soluble fiber to a diet low in saturated fat is thought to be modest.

Recognizing that maintaining an optimal weight to decrease the risk of chronic disease depends on balancing total energy consumption with energy expenditure, the DRI report targets a daily caloric intake based on the amount of physical activity an individual typically gets. A table lists the total number of calories (estimated energy requirements [EERs]) that is predicted to maintain energy balance consistent with good health in a healthy adult of a defined age, gender, weight, and height for each of four different physical activity levels (PALs). In children and pregnant and lactating women, the EERs take into account the needs associated with deposition of tissues or the secretion of milk. The DRI report recommends for the first time that total energy expended be at least 1.6–1.7 times an individual’s resting energy expenditure (considered an active lifestyle) in order to maintain body weight in the ideal range (body mass index [BMI] of 18.5–25 kg/m²), as well as decrease the risk of cardiovascular disease.

The AHA stresses that prevention of weight gain (<5 kg), particularly between the ages of 25 and 44 years, is a high priority, and when BMI is excessive (>30 or >25 kg/m² with comorbidities), weight reduction between 5 and 10% can reduce the risk for heart disease and stroke. Because of the challenge of achieving long-term weight maintenance after weight loss, the AHA points to the importance of primary prevention of obesity.

NCEP encourages weight reduction therapy for overweight and obese patients to enhance LDL cholesterol lowering.

The ADA acknowledges the benefits of modest weight loss, especially in improving insulin sensitivity in the short term (A level evidence). However, long-term studies are not available to determine whether this benefit continues over the long term, probably because weight loss is seldom maintained over the long term. In the UKPDS, even when weight loss was maintained, the improved fasting plasma glucose response was only maintained in patients who continued a restricted-energy intake.39 UKPDS researchers concluded that the reduction of energy intake was at least as important as, if not more important than, the actual weight lost in determining fasting plasma glucose.

Nutrition interventions such as standard weight-reduction diets, when used alone are unlikely to produce long-term weight loss (A level evidence). Structured, intensive lifestyle programs that emphasize education, reduced fat and energy intake, regular physical activity, and regular participant contact are necessary to produce long-term weight loss on the order of 5–7% of starting weight (A level evidence).

Furthermore, modest weight loss is most beneficial for individuals who are insulin resistant and for the prevention of type 2 diabetes.40,41 Once diabetes develops, it often is too late for weight loss to improve glycemic control42 because weight loss improves insulin resistance, not insulin deficiency. At this point, the focus on nutrition therapy must shift to lifestyle strategies that will improve glycemia, lipids, and blood pressure. Medications may need to be combined with nutrition therapy to achieve target glucose goals.

Based on a comprehensive review of the scientific data, the DRI panel found that in order to move from a very sedentary to an active lifestyle, adults and children alike need to engage in activities equivalent to a total of 60 minutes of moderately intense physical activity throughout the day.43–45 This new physical activity goal, while higher than the minimum goal of 30 minutes/day set by the 1996 Surgeon General’s Report for adults, may seem unrealistic. However, it includes everything an individual does beyond sleeping and breathing. Thus, gardening, dog walking, light housekeeping, and taking stairs instead of an elevator are all activities that contribute to an active lifestyle.

For example, someone in a largely sedentary occupation can achieve this new activity goal by walking at 4–5 miles per hour for a total of 60 minutes every day; jogging for 20–30 minutes 4–7 days/week; or doing the following: taking the stairs for a total of 10 minutes/day, walking for a total of 30 minutes during work and to the car or bus, raking leaves for 45 minutes, walking an hour while shopping, or spending an hour in the evening preparing dinner, cleaning up the kitchen, and walking the dog.

All three sets of guidelines from the health organizations support the importance of regular physical activity in reducing the risk of cardiovascular disease and promoting health. The AHA notes that physical activity is essential for maintaining physical and cardiovascular fitness. NCEP encourages moderate physical activity contributing ∼200 kcal/day to total energy expenditure. The ADA supports exercise as a means to improve insulin sensitivity, to acutely lower blood glucose levels, and to improve cardiovascular status. However, exercise by itself has only a modest effect on weight46 but is essential for the long-term maintenance of weight loss.47,48 Therefore, exercise is a useful adjunct to other weight loss strategies but is most helpful in weight maintenance (A level evidence).

Back to the original question: so many nutrition guidelines—contradictory or compatible? The answer is compatible, if you realize the population each set of guidelines is intended for. The DRIs are intended for a healthy population, their objective being to provide for vitamins, minerals, macronutrients, and energy needs by identifying ranges such that consumption above or below these ranges may be associated with nutrient inadequacy and increased risk of developing chronic diseases including coronary heart disease, obesity, type 2 diabetes, and cancer. The AHA nutrition guidelines also are designed for the general population, with the objective being to decrease the risk of cardiovascular disease by dietary and other lifestyle practices. The NCEP Adult Treatment Panel (ATP) III updates clinical guidelines for cholesterol testing and clinical management of high blood cholesterol. Although ATP III’s attention is to intensive treatment, including nutrition therapy, of patients with coronary heart disease, the major new feature of ATP III is attention to primary prevention in people with multiple risk factors. The ADA report provides evidence-based principles and recommendations for nutrition therapy in the treatment and, for the first time, prevention of diabetes. Therefore, although all the organizations review the same research studies, depending on their objectives, they develop nutrition guidelines for their intended populations.