Diabetes Mellitus: Nutritional Considerations

Prevention: Type 1 Diabetes

Dietary factors that may influence the risk of type 1 diabetes have been under investigation. The following considerations have emerged as potentially important candidates for preventive strategies:

• Breast–feeding: In some epidemiologic studies, breast–feeding is associated with reduced risk of developing type 1 diabetes. Longer duration of breast–feeding may be the key to reduced risk, presumably by increasing protection against infections, enhancing the infant’s immune responses, and delaying exposure to foreign food allergens. Although breast–feeding is the best choice for infant feeding, controlled trials of its effect on diabetes risk are difficult from ethical and practical standpoints and have not been conducted.
• Avoidance of early introduction of cow’s milk: Cow’s milk has been related to the diagnosis of diabetes, and children with type 1 diabetes have been found to have higher levels of antibodies against certain proteins contained in cow's milk. Although it has not yet been proven conclusively that cow’s milk is a trigger for type 1 diabetes, the American Academy of Pediatrics concluded that avoiding early exposure to cow’s milk may reduce the risk. An international study, the Trial to Reduce Type 1 Diabetes in the Genetically at Risk (TRIGR) study, has been designed to test the hypothesis that using a hydrolyzed formula instead of cow’s milk may delay or prevent the onset of type 1 diabetes in genetically susceptible children. Although the results of this study are pending, a smaller study with a similar design found that this intervention resulted in a significant protection from diabetes.
• Avoiding early introduction of gluten–containing foods: A higher prevalence of celiac disease has been observed in children with type 1 diabetes, compared with other children. In epidemiologic studies, supplementing infant diets with gluten–containing foods (e.g., wheat, barley, and rye) before the age of three months is associated with increased risk for developing antibodies typical of diabetes. In some children, both early (before three months) and late (after seven months) introduction of cereals was associated with increased risk.

Prevention: Type 2 Diabetes

Although type 2 diabetes has a strong genetic component, diet and lifestyle significantly affect the likelihood that the disease will occur. The risk for type 2 and gestational diabetes can be decreased by maintaining a healthy weight and a healthful diet.  

Individuals in Asia and Africa who follow traditional diets low in animal fat and high in complex carbohydrates have a far lower prevalence of diabetes than those who follow a Western diet. Vegetarians also have a lower prevalence of diabetes than meat–eaters.

These results are probably due to several factors. Intake of saturated fat is associated with high blood sugar, poor insulin action, gestational diabetes, and type 2 diabetes. In contrast, a higher intake of dietary fiber, particularly in the form of fruits and vegetables, results in lower blood sugar levels following meals. In addition, high–fiber diets often contain micronutrients important in regulation of blood sugar, including magnesium and vitamin E. 

The Diabetes Prevention Program (DPP) demonstrated that dietary changes designed to reduce body weight, combined with regular exercise, can significantly reduce the risk for type 2 diabetes. Specifically, risk was reduced by nearly 60 percent in the group that combined diet and exercise, compared with a 30 percent reduction for those on drug treatment. In individuals age 60 and older, the risk was reduced more than 70 percent with diet and exercise, while drug treatment was not effective for persons older than 45 years.

Nutritional Management of Diabetes

The goals of nutrition therapy in diabetes management include control of blood sugar at near–normal levels, maintenance of healthy blood pressure and cholesterol levels, and attainment of a healthy weight. Adherence to a healthful diet, regular exercise, and use of medications when necessary may achieve these goals and help minimize the risk of complications.    

• Maintenance a healthy weight: Current guidelines of the American Diabetes Association prescribe a calorie–controlled meal plan that uses food exchange lists that keep carbohydrate intake reasonably steady throughout the day and from one day to the next. The guidelines also limit saturated fat and cholesterol. Advantages of this approach include flexibility and the allowance of most foods, albeit in limited amounts. Its disadvantages include the need to measure foods and the difficulty in restricting calories over the long term. Such diets require ongoing education and monitoring, which should generally be provided by a registered dietitian in a series of visits.
  
  Recent studies suggest that low–fat, plant–based diets may be more effective for weight loss, blood sugar control, and reduction of cardiovascular risk factors, particularly blood cholesterol. Such diets may also be easier for patients to follow. A low–fat, plant–based diet works in several ways. First, because such diets are low in fat, they tend to be low in calories. And because they are high in fiber, they are filling. The result is a low calorie intake and easy weight loss, an important effect given that increased body fat is associated with diabetes. A recent study showed that a low–fat, vegan diet led to greater weight loss and blood glucose control, compared to a diet following American Diabetes Association guidelines.
• Carbohydrate type may influence blood sugar control: A review of five studies of individuals with type 1 or type 2 diabetes showed that diets with fewer simple sugars improved glucose control. Furthermore, diets richer in fiber tend to produce lower blood sugar levels after meals, compared with fiber–depleted diets, and high–fiber diets have been shown to improve control of blood sugar in individuals with type 2 diabetes. Because vegan diets consist solely of plant–derived foods, they are typically high in fiber, compared with non–vegan diets, provided the diet does not rely heavily on processed foods.
  
  The glycemic index is a means of rating the effect of various foods on blood glucose. High–glycemic–index foods tend to raise blood sugar rapidly. These include sugar, wheat breads, baking potatoes, and most cold cereals. Low–glycemic–index foods tend to have less effect on blood sugar. These include beans, rye or pumpernickel bread, yams, sweet potatoes, oatmeal, bran cereals, and most vegetables and fruits. Favoring low–glycemic–index foods may help control blood glucose and may also reduce triglycerides (blood fats).
• Excess body iron stores may increase the risk for diabetes: Limited evidence suggests that elevated body iron stores are associated with diabetes, and lowering the excess iron (by dietary changes or blood donation) may decrease the risk. A study comparing 30 vegetarians and 30 meat–eaters, all of whom were healthy and had normal body weights, showed that the vegetarians had adequate, but lower, body iron stores, compared with the meat–eaters. The vegetarians also demonstrated less risk for diabetes than the meat–eaters.

Similar dietary changes are helpful for patients with type 1 diabetes. A high–fiber diet results in lower insulin requirements and improved management of blood sugar and cholesterol.

Gestational diabetes

Further study is needed to establish optimal dietary interventions in gestational diabetes. Some evidence suggests that a diet limiting carbohydrates to 40 percent of calories, with fat providing 40 percent and protein providing the remaining 20 percent, improves control of blood sugar and reduces the need for insulin injections. Future studies are required to compare a carbohydrate–reduced diet with a low–fat, high–fiber diet, particularly a vegan diet.

Vegan diets may present a clinical advantage because they include no animal fat, and increases in food quantity are less likely to result in substantial increases in saturated fat intake. While vegetarian or vegan diets may sound restrictive at first glance, their acceptability in clinical studies is similar to that of other types of diets. Because vegan diets do not limit portions, calories, or carbohydrates, they may be simpler to follow than regimens that limit quantities of certain foods.

Dietary Supplements in Type 2 Diabetes

Several supplements have been investigated for their role in diabetes management, notably chromium and certain botanicals:

• Chromium: Chromium is believed to increase the body’s response to insulin. However, studies in individuals with type 1, type 2, or gestational diabetes, including trials using daily doses as high as 1,000 mcg of chromium, have yielded mixed results. Thus, most diabetes authorities do not recommend chromium supplements.
  
  According to the Food and Nutrition Board of the Institute of Medicine, the safe and adequate daily intakes of chromium for adults 19 to 50 years of age are 35 mcg for men and 25 mcg for women. For people over 50, the numbers are 30 mcg for men and 20 mcg for women. Most common multiple vitamins include chromium, usually in amounts ranging from 100 to 200 mcg.
• Botanicals: The role of certain botanicals for patients with type 2 diabetes is also under investigation. Metformin, a common diabetes drug, was developed from Galega officinalis (French lilac). Ginseng has been found in small studies to lower blood sugar levels after large meals. Bitter melon (Momordica charantia), a botanical with insulin–like effects, has also demonstrated blood sugar–lowering effects in humans.
  
  In spite of these initial benefits, problems remain with the use of botanicals in diabetes. First, clinical trials of ginseng and bitter melon have included only small numbers of persons, yielding inconclusive results. Another problem is the lack of standardization of active ingredients.