According to a new American study, a high-protein diet may lead to lower plasma glucose concentrations in people with type 2 diabetes. Dietary recommendations for both healthy and diabetic persons have traditionally focused on carbohydrate and fat intake, with protein being largely disregarded. However, several single-day and single-meal studies have suggested that protein ingestion may actually lead to a decrease in postprandial glucose concentrations.
Mary C. Gannon, MD, of the Veterans Affairs Medical Center, Minneapolis, Minnesota, and colleagues conducted a study to examine the effect of a high-protein diet on glucose levels over a longer term.
Twelve subjects with mild, untreated type 2 diabetes (mean age, 61 years; 10 males) were randomly assigned to either a control diet designed according to the recommendations of the American Diabetes Association (protein:carbohydrate:fat, 15:55:30) or a high-protein diet (30:40:30) for a period of 5 weeks. The subjects were given a 2 to 5 week washout period after the first 5-week phase, and then switched to the opposite diet for a second the following 5 weeks.
Dr. Gannon found that fasting glucose concentration was consistently lower after the high-protein diet, with no significant change in body weight. The mean 24-hour integrated glucose area responses (with fasting glucose concentration as baseline) were 34.1 ± 7.2 mmol x h/L and 21.0 ± 4.2 mmol x h/L after the control and high-protein diets, respectively, revealing a 40% decrease with the high-protein diet.
The high-protein diet also showed a greater decrease in the mean total percent glycated haemoglobin (0.8%) compared with the control diet (0.3%, P<0.05), with a significantly greater rate of decline (P<0.001).
The insulin area response was 18% greater with the high-protein diet, but not significantly different from the control diet. This response was less than expected based on previous single-meal and single-day studies. The cause of the smaller response in the present study is uncertain, but the researchers suggest that it “may be due to a corresponding decrease in carbohydrate in the diet.”
Triacylglycerol concentration decreased with the high-protein diet, whereas the total cholesterol and HDL and LDL cholesterol were unchanged. However, Dr. Gannon notes that, “these data must be interpreted with caution because some subjects were taking medications for lipid control.”
“The data suggest that a high-protein diet may improve blood glucose control in persons with type 2 diabetes,” the researchers conclude, but they recommend that “longer term studies are necessary to determine potential adverse effects of such a diet, if any.” Am J Clin Nutr 2003 Oct;78:4:734-41.