American Diabetes Association Guide to Nutrition Therapy for Diabetes. Marion J. Franz

intakes were associated with worse glycemic control at year 5 compared to a higher carbohydrate (56%) intake (A1C values of 7.5 versus 7.0%, respectively), independent of exercise and BMI (Delahanty 2009). The authors suggest that the carbohydrate content is less critical than the total and saturated fat content, to which it is usually inversely related. They note that high-fat meals have been shown to interfere with indexes of insulin signaling, which results in a transient increase in insulin resistance (Savage 2007), and that a lower-fat diet reduces basal free fatty acid concentrations and improves peripheral insulin sensitivity in type 1 diabetes (Rosenfalck 2006).

      To determine the effects on CVD risk factors in people with type 1 diabetes, a eucaloric diet higher in carbohydrate and lower in fat was compared to a diet lower in carbohydrate and higher in monounsaturated fatty acids (MUFAs). After 6 months, there were no significant differences between groups other than decreased plasminogen activator inhibitor 1 and weight gain in the lower-carbohydrate/MUFA group. This result suggests that if individuals choose to lower carbohydrate intake, these calories should be replaced with unsaturated fats rather than saturated fats and special attention should be paid to total energy intake (Strychar 2009).

      Type 2 Diabetes

      A cross-sectional study of American Indians with type 2 diabetes in the Strong Health Study assessed dietary intake in 1,284 participants. Lower intake of carbohydrate (<35–40% of energy) and higher intakes of total (>25–30% of energy) and saturated fats (>13% of energy) were associated with poorer glycemic control. A lower fiber intake and a higher protein intake were marginally associated with poor glycemic control (Xu 2007).

      Clinical trials in individuals with diabetes have compared lower carbohydrate intakes and higher total fat and saturated fat intakes to higher carbohydrate intakes and lower total fat and saturated fat intakes. A meta-analysis of 19 short-term studies (10 days to 6 weeks) with 306 individuals with type 2 diabetes compared lower-carbohydrate, higher-fat diets (40%/40%) to higher-carbohydrate, lower-fat diets (58%/24%) and found no significant differences between diets in the reduction in A1C and total and LDL cholesterol. The higher-carbohydrate diets did increase triglyceride levels and decrease HDL cholesterol. However, the higher-carbohydrate diet did not elevate triglycerides when energy restriction was prescribed. Therefore, total energy intake is a factor when determining the effect of carbohydrate on triglyceride levels. Studies in which glucose-lowering medications were changed and that included an increase in fiber and whole grains were excluded from the meta-analysis because such diets are high in fiber, which in itself has beneficial effects on glycemia and lipemia, regardless of the carbohydrate-to-fat ratio (Kodama 2009). In general, total and LDL cholesterol change more favorably in individuals assigned to low-fat/higher-carbohydrate diets, whereas, HDL cholesterol and triglyceride values change more favorably in individuals randomized to low-carbohydrate diets (Nordmann 2006).

      Since publication of the meta-analysis, three 1-year studies in people with type 2 diabetes comparing higher-carbohydrate diets to lower-carbohydrate, low-fat, or high-MUFA diets have been published and reported no differences in A1C, weight loss, LDL cholesterol, triglycerides, or blood pressure (Brehm 2009; Davis 2009; Wolever 2008). Vegetarian and vegan diets are high in carbohydrate. A vegetarian diet (52% energy from carbohydrate) was compared to a diet high in MUFAs, with reported beneficial effects from the vegetarian diet on lipids (total cholesterol, LDL cholesterol, postprandial triglycerides), glucose, and insulin levels (De Natale 2009). A 22-week low-fat vegan diet (75% carbohydrate) compared to a control diet (60–75% carbohydrate and MUFAs) showed greater improvements in A1C levels (~1% point reduction), body weight, and lipids (total and LDL cholesterol, triglycerides) from the vegan diet in secondary analysis. The intent-to-treat analyses, however, showed no significant differences between groups (Barnard 2006).

      In summary, in observational studies in people with type 1 and type 2 diabetes, higher-carbohydrate diets compared to diets higher in total fat and saturated fat are associated with lower A1C levels. However, in clinical trials, both high- and low-carbohydrate diets lead to similar improvements in A1C and body weight. It appears likely that the total energy intake of the eating pattern outweighs the distribution of carbohydrates. High-carbohydrate diets, which are generally low in fat, tend to have beneficial effects on total and LDL cholesterol, whereas low-carbohydrate diets tend to have beneficial effects on triglycerides and HDL cholesterol. Because of beneficial and/or similarities in outcomes, it would seem prudent to recommend an eating pattern with moderate amounts of carbohydrate (which is how many people with diabetes already eat) and that includes fruits, vegetables, whole grains, and low-fat dairy foods—all carbohydrate sources—in appropriate amounts and portion sizes.

      Types of Carbohydrate

      Sucrose. After reviewing 15 studies in which sucrose was substituted for isocaloric amounts of starch, the Acad Nutr Diet EBNPG concluded the following: “If persons with diabetes choose to eat foods containing sucrose, the sucrose-containing foods can be substituted for other carbohydrate foods. Sucrose intakes of 10% to 35% of total energy do not have a negative effect on glycemic or lipid level responses when substituted for isocaloric amounts of starch” (Acad Nutr Diet 2008; Franz 2010). The ADA also concluded, “sucrose-containing foods can be substituted for other carbohydrates in the meal plan, or, if added to the food/meal plan, covered with insulin or other glucose-lowering medications” (ADA 2008). However, as with the general public, care should be taken to avoid excess energy intake, and excessive intake of sugars should be avoided in a healthier eating pattern. The DGAC recommends a maximal intake level of ≤25% of total energy from added sugars, based on research showing that people with intakes of added sugars at or above this level are more likely to have poorer intakes of important essential nutrients (DGAC 2010). For a daily energy intake of ~2,000 kcal, this would be about 10 teaspoons of added sugars; however, average intake for all individuals in the U.S. is ~22 teaspoons per day. (One 12-ounce can of cola contains ~8 teaspoons of added sugar, for ~130 kcal.) In general, it is recommended that most women should eat or drink no more than 100 kcal/day from added sugars and most men no more than 150 kcal/day (Johnson 2011).

      There is a natural liking of sweet tastes and, in that regard, people with diabetes are similar to people without diabetes. Unfortunately, people with diabetes are often made to feel guilty if they choose foods that contain added sugars. Knowing the total carbohydrate content, including sugars, of foods can assist people with diabetes to make appropriate food choices that they will enjoy while maintaining glycemic control.

      High-fructose corn syrup. High-fructose corn syrup is composed of either 42 or 55% fructose and is similar in composition to table sugar (sucrose). Therefore, the recommendations discussed above related to sucrose also apply to high-fructose corn syrup. High-fructose corn syrup does not differ uniquely from sucrose and other nutritive sweeteners in metabolic effects (glucose, insulin, and triglycerides), subjective effects (hunger, satiety, and energy intake at subsequent meals), and adverse effects such as weight gain (Acad Nutr Diet 2012). It is the sweetener commonly used by the beverage industry.

      Fiber and whole grains. Foods containing fiber and whole grains are also recommended. After reviewing 15 studies reporting on the effect of fiber intake on glycemic and lipid outcomes in individuals with diabetes, the Acad Nutr Diet EBNPG concluded the following: “While diets containing 44 to 50 g fiber daily are reported to improve glycemia in persons with diabetes, more usual intakes (up to 24 g/day) have not shown beneficial effects on glycemia. Recommendations for fiber intake for people with diabetes are similar to the recommendations for the general public (DRI: 14 g/1,000 kcal)” (Acad Nutr Diet 2008; Franz 2010). However, the guidelines do recommend including foods containing 25–30 g fiber per day, with special emphasis on soluble fiber sources (7–13 g) because of their beneficial effect on lipids.

      The ADA also recommends that people with diabetes choose a variety of fiber-containing foods such as legumes, fiber-rich cereals (≥5 g fiber/serving), fruits, vegetables, and whole-grain products because they provide vitamins, minerals, and other substances important for good health. The first priority is to achieve fiber-intake goals set for the general population of 14 g/1,000 kcal (ADA 2008). Interestingly, the DGAC notes that it is difficult to meet dietary fiber recommendations with a low carbohydrate intake (DGAC 2010).

      However, consumption of whole-grain foods is likely to be of equal importance