Low-Carb Diets and Diabetes: Just What the Doctor Ordered?

MARCH 01, 2005
Anna D. Garrett, PharmD, BCPS, CPP

Atkins, Zone, Sugar Busters, Protein Power, South Beach—the list of high-protein fad diets is seemingly endless. All of these diets reduce the amount of carbohydrates ingested and promise rapid weight loss. Yet, are these diets safe for people with diabetes?

Maintaining a healthy weight is important for both the prevention and the treatment of diabetes. Obesity increases the risk of developing diabetes. For people with the disease, weight loss can improve blood glucose control and prevent long-term complications. Losing weight is difficult, however, and people often resort to diets that are unbalanced and potentially unsafe. The latest craze is lowcarb diets, which severely restrict carbohydrates. It is claimed that these diets reduce insulin production through carbohydrate restriction, which then results in weight loss.

People do lose weight on high-protein, low-carbohydrate diets. The weight loss, however, is largely due to water loss and reduced calories, not lower insulin levels as claimed by the authors. Nutrition experts generally do not recommend these diets for people with diabetes: these diets are difficult to maintain over a long period of time, and higher fat and protein intake may increase the risk of coronary heart disease (CHD) and kidney damage—2 conditions for which diabetics are already at high risk.

Diets that are high in protein tend to be high in fat. The Atkins Diet, which encourages high intake of meats, eggs, and dairy products, provides about 20% to 25% of calories from saturated fat. The South Beach Diet encourages a more moderate approach, limiting highfat cuts of meat and high-fat dairy products. The American Diabetes Association (ADA) recommends that no more than 10% of calories come from saturated fat.

Diets high in saturated fat may raise blood cholesterol levels, which then increase the risk of CHD. Two studies of the Atkins Diet found increased cholesterol in the participants.1,2 The researchers in one of the studies calculated that long-term use of this diet would result in a 25% increase in cholesterol, which translates into a 50% increased risk of CHD. Another study of a low-fat versus low-carb diet in obese patients demonstrated stable cholesterol levels in the low-carb group. The recommended diet in this study, however, encouraged use of low-fat cuts of meat and reduced-fat dairy products.3 Weekly diet counseling was provided in the study as well.

High-protein diets also tend to be low in fiber, which may increase the risk of CHD. The ADA recommends 20 to 35 g of fiber per day. The Atkins and Protein Power diets supply only 5 to 10 g per day. Research has shown that foods high in soluble fiber—such as bran, beans, and apples—can lower cholesterol levels. High-protein diets may increase the risk for renal dysfunction in people with diabetes or exacerbate problems that already exist. The ADA recommends no more than 20% of calorie intake from protein. Protein intake in most of the low-carbohydrate diets is 28% to 35% of calories. High-protein, low-carb diets induce ketosis, which may lead to diabetic ketoacidosis, a medical emergency.

The scientific evidence surrounding the effects of low-carbohydrate diets is not clear. A recent review of clinical trials assessing the relative effects of fat versus carbohydrate, the difference between fatty acids and the types of carbohydrate on insulin resistance, and associated risk factors for diabetes and cardiovascular disease concluded that diets higher in monounsaturated fatty acids, fiber, and low-glycemic index foods showed advantages in reducing risk factors for chronic disease, especially those associated with insulin resistance.4 The Steno-2 trial, conducted in patients with type 2 diabetes, showed fewer cardiovascular events despite consumption of a high-carb, low-fat diet over an 8-year period.5 A recent review of studies of low-carb diets found no advantage to these diets, when compared with balanced diets that contained carbohydrates.6

Currently available scientific evidence does not support the recommendation of low-carbohydrate diets for people with diabetes. All carbohydrates are not the same. The American diet contains large amounts of processed, high-fat, calorie-dense foods, such as fast food. Our carbohydrate choices have typically favored high-sugar, low-fiber carbohydrates that have relatively little nutritional value. A more sensible approach to weight management in diabetes would include a diet with fruits, vegetables, and whole grains, as well as foods low in saturated fat—plus a regular dose of exercise.

Dr. Garrett is a clinical pharmacist practitioner at Cornerstone Health Care, High Point, NC.

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