The American Diabetes Association (ADA) periodically revises dietary guidelines for persons with diabetes mellitus. Most recently, the replacement of saturated fats with carbohydrates or, alternatively, with cis monounsaturated fats was recommended. An increase in dietary fiber, from 20 to 35 g per day, was recommended as well, given the observed benefit of fiber in lowering cholesterol. The ADA, however, has not acknowledged the effects of dietary fiber on glycemic control. Chandalia and colleagues assessed the effect of increased dietary fiber on blood glucose control and plasma lipid concentrations in patients with type 2 diabetes (formerly known as non–insulin-dependent diabetes).
Adults with type 2 diabetes mellitus with onset of disease after age 40 were eligible for the study. Patients were admitted to a clinical research center for a five-day baseline period, during which time a history was obtained. A physical examination and baseline laboratory tests were conducted. For the first six weeks, one half of the patients consumed a standard ADA diet, and one half received a high-fiber diet. For details on the composition of the diets, see the accompanying table
. After a one-week interval in which the patients consumed an isocalorie diet, all crossed over to receive the opposite diet.
Blood for lipid analysis was drawn two days before the study diet and daily on days 38 through 42 of both dietary periods. Plasma glucose was drawn four times daily during the baseline period and on days 38 to 42 of both dietary periods. Glycosylated hemoglobin levels were evaluated at baseline and at the end of each dietary period. Finally, plasma glucose and insulin levels were checked every two hours on the last day of each dietary period.
Thirteen persons were enrolled in the study (12 men and 1 woman), and compliance with the two diets was reported as “excellent” based on interviews and estimates of leftover foods. During the last week of each dietary period, participant body weight (approximately 90 kg [198 lb]) and caloric intake (approximately 2,300 kcal per day) were similar. At the end of each dietary period, mean plasma glucose levels were 13 mg per dL (0.72 mmol per L) lower in participants consuming the high-fiber diet compared with those consuming the ADA diet. In addition, daily plasma glucose and plasma insulin concentrations were 10 and 12 percent lower, respectively, in participants consuming the high-fiber diet. Compared with the ADA diet, the high-fiber diet also lowered total cholesterol by 6.7 percent, triglyceride concentrations by 10.2 percent (205 versus 184) and low-density lipoprotein cholesterol concentrations (6.3 percent).
The authors conclude that a high-fiber diet, emphasizing soluble fibers, improves glycemic control and reduces insulin and cholesterol levels. They note that in the United States, the average daily intake of fiber among persons with diabetes is only 16 g. They emphasize that dietary guidelines for patients with diabetes should strongly encourage an overall increase in dietary fiber through the consumption of unfortified foods rather than fiber supplements.