January 2008: Restricted Carbohydrate Diets in Patients with Type 2 Diabetes: A Meta-Analysis

Interest in carbohydrate restricted diets has seen a dramatic increase throughout the general population. Some research has even suggested that diets low in carbohydrate content may provide greater weight loss in the short term. Since many Type 2 Diabetes patients are overweight, which can contribute to a higher risk for diabetes related complications, an interest in recommending carbohydrate restricted diets for quick weight loss in this population has developed. One of the possible issues with this diet being recommended to diabetic patients is that it may accelerate the reduction of renal function. The mechanism behind this concern stems from protein making up the calorie difference, which in return makes the kidneys work harder. Research in this area has left the risks and benefits unclear for this population of patients.

The American Diabetes Association does not recommend diets less than 130 grams of carbohydrate per day, but many of these carbohydrate restrictive diets are far less than this guideline. According to the article, the National Academy of Sciences recommends 45%-65% of total calories come from carbohydrate per day in order to provide adequate amounts of energy in the form of glucose, essential vitamins and minerals, and dietary fiber. If following a restrictive diet at 130 grams of carbohydrate or less, the daily carbohydrate percent will not fall in this recommended range even if one is only consuming 1200 calories a day.

This meta-analysis included studies with carbohydrate restrictions of 4%-45% of calories coming from carbohydrates. In order to meet criteria the studies also had to analyze the outcomes of weight loss, triglycerides, cholesterol (including LDL, HDL, and total), hemoglobin A1c, and fasting glucose related to the specific percent of carbohydrate restricted. The database resulted in 329 articles related to Type 2 Diabetes and carbohydrate content with participants ranging from 48-66 years old. Various techniques were used throughout the studies to monitor compliance to the low carbohydrate diet proposed in each scenario.

After reviewing the results of all of the included studies, glycemia, lipid values, and weight loss were looked at. In the majority of the studies looking at the effects of carbohydrate on glucose levels, hyperglycemia and hemoglobin A1C were reduced when on a carbohydrate restricted diet. No significant relationships were noted for choleterol (LDL, HDL, or total) or for weight loss, but a significant reduction in triglyceride levels was seen with the low carbohydrate diet. According to the data examined, the meta-analysis concluded that a diet lower in carbohydrate may be beneficial to those with Type 2 Diabetes. Although, due to the many limitations noted throughout the current research, the article suggests conducting further studies with a longer duration to assess the long term effects of a carbohydrate restricted diet.

The first additional article reviews medical nutrition therapy guidelines for Type 2 Diabetes that are currently being practiced. Although the article is assessing diabetes management outcomes at a single site, it provides details as to what medical nutrition therapy guidelines should be used for diabetes management at this time. The second article reviews a workshop held by the International Life Sciences Institute (ILSI) where they discussed what was known and unknown related to low carbohydrate diets. In the adult population, the group concluded more long term studies were needed to assess the risks and benefits of this diet on the general population.

JADA Continuing Education Article:

Austin, M., Craven, T., Graves, D.E., Kirk, J.K., Lipkin, E.W., & Margolis, K.L. (2008). Restricted Carbohydrate Diets in Patients with Type 2 Diabetes: A Meta-Analysis. Journal of the American Dietetic Association, 108(1), 91-100.

Additional Articles:

Conley, L., Mancino, J.M., & McHattie, K. (2002). Comparison of Type 2 Diabetes Medical Nutrition Therapy to Practice Guidelines in a Community Health System. Journal of the American Dietetics Association, 102(8), 1129-1131.

Jones, J.M., Levine, M.J., Lineback, D.R. (2006). Low Carbohydrate Diets: Assessing the Science and Knowledge Gaps, Summary of an ILSI North America Workshop. Journal of the American Dietetics Association, 106(12), 2086-2094.