Dietary therapy in diabetes mellitus: Is there a single best diet?

The ideal diet for diabetic patients remains to be determined. Recommendations generally call for low-fat high-carbohydrate diets. The primary purpose of this recommendation is to reduce the risk for coronary heart disease, a major killer of diabetic patients. Some investigators also suggest that high-carbohydrate diets also improve glucose tolerance, even in patients with non-insulin-dependent diabetes mellitus (NIDDM). Another potential advantage of a low-fat diet (high percentage of carbohydrate) is that it may promote weight reduction. High-fat diets are thought by many investigators to stimulate weight gain. Thus, in obese NIDDM patients a trial of a low-fat weight-reduction diet may be worthwhile. However, if after an adequate trial of this diet, weight reduction is not achieved, this suggests that the patient is consuming large quantities of carbohydrates. The continued feeding of a high-carbohydrate diet to a persistently obese patient with NIDDM may have several untoward effects. For example, it can heighten hyperglycemia, raise plasma triglycerides, and lower high-density lipoproteins. In such dietary failures, it may be better to replace carbohydrate with fat to avoid these responses. Ideally, the fat should not raise the serum cholesterol level, and hence it should be unsaturated. Monounsaturated fatty acids seem preferable to polyunsaturated fatty acids, because polyunsaturates may increase the risk for cancer or promote the oxidation of low-density lipoprotein, another potentially atherogenic change. Many NIDDM patients. particularly obese patients in the earlier stages of diabetes, tolerate weight-maintenance high-carbohydrate diets without deterioration of glucose tolerance. However, as their insulin reserve declines, high-carbohydrate diets may further raise glucose levels, and a lower-carbohydrate diet seems preferable. The same may be true for nonobese patients with NIDDM; the predominant defect in many of these patients is a deficient secretion of insulin. Replacement of carbohydrates by monounsaturated fatty acids in the latter two groups of patients may be advantageous. In summary, the best dietary approach in obese patients with NIDDM, who are relatively early in the course of their disease, is to attempt weight reduction with a low-fat diet. However, if this diet should fail, it probably would be better to reduce carbohydrate intake and replace some of it with monounsaturates. Likewise, in more advanced NIDDM, with deficiency of insulin secretion, high-carbohydrate diets probably should be avoided, because they accentuate hyperglycemia. Therefore, the ideal diet for diabetic patients may depend on the presence or absence of obesity, the response to a weight-reduction diet, and the stage of progression of β-cell dysfunction.