The most important dietary goal for individuals with type I diabetes mellitus is the establishment of a regular meal pattern with consistent day-to-day caloric and carbohydrate intake. Ideally, the diet should contain 55 to 60 per cent of total calories as carbohydrate, less than 30 per cent of calories as fat, less than 10 per cent of calories as saturated fat, and less than 300 mg of cholesterol per day. The best tool for helping type I individuals achieve these objectives is the Exchange Lists for Meal Planning. A second important dietary goal in type I diabetes is to avoid weight gain during intensive treatment programs. The most important dietary and therapeutic goal in obese persons with type II diabetes is weight loss. Unfortunately, no dietary method, whether initiated by self-help groups like TOPS, physicians, or other health care professionals, has been demonstrated to be effective in achieving and maintaining weight loss. Nevertheless, some individual patients will be successful, and it therefore is appropriate to attempt weight reduction with a balanced diet moderately restricted in calories. A reduction of 500 calories per day below the weight maintenance level is reasonable and can be expected to produce weight loss of about 1 lb per week. For those type II diabetic patients who are not able to lose weight and are at least twice their ideal body weight, gastric reduction surgery could be considered. The Glycemic Index of Foods is a new concept that has not been evaluated adequately. Recent evidence suggests that differences among foods are reduced when the foods are combined in a meal and thus raises questions about the utility of glycemic indexing. The longstanding restriction on the use of sucrose in the diabetic diet is without scientific basis. Recognizing this, the American Diabetes Association recently sanctioned consumption of modest amounts of sucrose in the diabetic diet. Although conclusive evidence is not yet available that high fiber diets improve glycemic control or reduce serum lipids in diabetic persons, it appears reasonable to encourage the consumption of natural foods high in soluble fiber. Vegetables (particularly legumes), oats, and many fruits are good sources. The American Diabetes Association recommends a goal of 40 g of soluble fiber intake per day. The dietary treatment of diabetes is likely to be more successful if physicians learn more about its essential features and pay it greater attention. The goals of dietary therapy are difficult to achieve and often require significant sacrifices.(ABSTRACT TRUNCATED AT 400 WORDS)