Higher Carbohydrate Wins

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Most people with type 2 diabetes would better their health if they lost weight. Losing even modest amounts of body fat often improves insulin sensitivity, which reduces or eliminates the need for medications to lower blood sugar levels. Insulin resistance puts those with type 2 diabetes at much higher risk for cardiovascular disease.

Weight control is also important for reducing other risk factors for cardiovascular disease, such as high blood pressure and dyslipidemia (disorder of fats in the blood).


Most researchers agree that in addition to reduced calorie intake, the best diet for those with type 2 diabetes is reduced in saturated fat, trans fat, refined sugars and grains, cholesterol and salt. It should also be higher in fiber. However, there is still disagreement about the optimal ratio of fat, protein and carbohydrate.


The popularity of a low-carbohydrate diet, such as the one advocated by Atkins, is fading because it is high in saturated fat and cholesterol and low in fiber. Because this diet emphasizes animal products (most high in saturated fat and/or cholesterol), it seems a poor choice for people at high risk for cardiovascular disease such as those with type 2 diabetes.


Is high-protein with less fat ideal?


In the 1990s, diets with more protein and less carbohydrate became increasingly popular for weight loss because of some evidence suggesting they might make weight loss easier. Increasingly, people with type 2 diabetes are adopting lower-carbohydrate and higher-protein diets for this same reason.


Perhaps the best known of these diets is the “Zone Diet” created by Barry Sears, Ph.D. Sears advocates a diet with a ratio of fat to protein to carbohydrate of 30/30/40, respectively.

Little research exists regarding the impact of eating more protein at the expense of carbohydrate. Therefore, researchers at Temple and Drexel Universities in Philadelphia decided to examine the impact of differing ratios of protein and carbohydrate in a group of obese type 2 diabetes subjects. They randomly assigned two similar groups to follow either a typical weight-loss diet with about 55% carbohydrate and 15% protein (similar to the National Cholesterol Education Program guidelines) or a “Zone-like” diet for 2 months.


Both diets had a similar fat content and both diets provided about the same number of calories. The Zone-style diet did turn out to be significantly higher in fiber and also had significantly less salt and a much higher potassium-to-sodium ratio than the NCEP-style diet. Researchers measured blood-sugar levels, insulin sensitivity and other cardiovascular-disease risk factors at the beginning and end of the 2-month experimental diet period.


The study’s results showed weight loss after 2 months on the two diets was similar. Subjects lost 4.8 pounds on the higher-carbohydrate diet and 5.5 pounds on the higher-protein diet. Given the similar weight loss and fat loss in both groups and the similar intake of fat, cholesterol and fiber, a similar but modest improvement in blood lipids in both groups was predictable. Blood pressure did drop significantly on the higher protein diet, but as the researchers noted in their paper this was likely the result of reduced intake of salty snacks and increased vegetable snacks on the higher-protein diet.


Higher-protein diet worse for blood sugar control


The subjects following the higher-carbohydrate diet experienced significantly greater improvement in fasting blood sugar levels, glycosylated hemoglobin levels (HbA1c) and insulin sensitivity relative to the higher-protein diet. So why did the higher-protein diet fail to improve blood-sugar regulation as much as the higher-carbohydrate diet despite equal or slightly greater weight and body fat loss? Subjects on the higher-protein diet had significantly higher fasting free fatty acid (FFA) levels than those on the higher carbohydrate diet (714 vs. 527mmol/L). Higher FFA levels are known to interfere with the insulin-mediated removal of sugar from the blood stream resulting in more insulin resistance. While this was a small study, the results are consistent with earlier data and strongly suggest that a diet with more protein and less carbohydrate may very well be inferior to one higher in carbohydrate for most people with type 2 diabetes.1


By James J. Kenney, PhD, RD, FACN




1 J Am Diet Assoc. 2005;105:573-80

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