Short-Term Effects of Low-Carbohydrate Diet Compared with Usual Diet in Obese Patients with Type 2 Diabetes

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The summary below is from the full report titled "Effect of a Low-Carbohydrate Diet on Appetite, Blood Glucose Levels, and Insulin Resistance in Obese Patients with Type 2 Diabetes." It is in the 15 March 2005 issue of Annals of Internal Medicine (volume 142, pages 403-411). The authors are G. Boden, K. Sargrad, C. Homko, M. Mozzoli, and T.P. Stein.

What is the problem and what is known about it so far?

Low-carbohydrate diets are popular among people who want to lose weight. Some studies show that people lose weight more quickly with low-carbohydrate diets than with diets that restrict calories and fat. It is not clear whether the more rapid initial weight loss with a low-carbohydrate diet is due to eating fewer calories or to some other factor, such as greater loss of body water. Some worry that low-carbohydrate diets might have an unfavorable effect on risk factors for heart disease, such as cholesterol levels. However, low-carbohydrate diets may be beneficial for other metabolic factors, such as blood sugar, that are linked to diabetes.

Why did the researchers do this particular study?

To describe the changes in weight, body water, appetite, blood sugar level, and cholesterol level that occurred when obese patients with type 2 diabetes switched from their usual diet to a low-carbohydrate diet.

Who was studied?

10 volunteers with type 2 diabetes who were very obese (average body mass index was more than 40 kg/m²).

How was the study done?

During the study, the patients stayed in a research center of the hospital. For the first 7 days, patients ate their usual diet. For the next 14 days, they followed a low-carbohydrate diet (about 21 grams of carbohydrates per day). Before, during, and after each diet, the researchers measured many factors, including body weight, body water, calorie energy intake, appetite hormone levels, and several measures of blood sugar control.

What did the researchers find?

On average, patients lost 1.65 kg after 14 days on the low-carbohydrate diet. On average, patients reduced their calorie intake from 3111 calories per day to 2164 calories per day when on the low-carbohydrate diet. This reduction in calorie intake explained the weight loss. Weight loss was not due to loss of body water. Blood sugar and cholesterol levels improved during the low-carbohydrate diet.

What were the limitations of the study?

This study included a small number of patients who were studied for a short period of time in a very controlled research setting.

What are the implications of the study?

Reduced calorie intake seems to account for weight loss associated during the first 2 weeks of a low-carbohydrate diet. Low-carbohydrate diet improves blood sugar and cholesterol levels in obese patients with type 2 diabetes.