Does a diet that’s high in carbs—or high in the wrong carbs—raise your risk of diabetes? The answers are still murky.
When two large European studies pitted higher-carb diets against diets higher in monounsaturated fats, insulin sensitivity —that is, how much insulin it takes to remove a given amount of sugar from the blood—didn’t change.
Nor does insulin sensitivity consistently change when researchers test high-glycemic carbs (which give blood sugar a big boost) against carbs with a low glycemic index.
“The literature does not support glycemic index making a big difference in insulin sensitivity, or much of anything besides short-term blood sugar levels,” says Frank Sacks, professor of cardiovascular disease prevention at the Harvard School of Public Health.
And so far, large studies that swap white bread and other refined grains for whole grains have largely come up empty.
Still, Sacks and other researchers argue that it’s worth cutting back on carbs to lower blood sugar and insulin levels after meals.
“We can’t say that reducing carbohydrate improves insulin sensitivity, but it reduces the need for more insulin,” says Sacks. “It’s logical that if you eat less carbs, less glucose will go into the bloodstream and stimulate the pancreatic beta cells to secrete insulin.”
And there isn’t much room for white flour and added sugars in a diet that’s rich in vegetables, fruits, beans, and other healthy carbs.
“So to simplify the message, let’s just say that in a more healthful diet, carbohydrate is lower—not extremely low, but at the lower end of the range of what many people now eat,” says Sacks.
“And for the carbs that you eat,” notes Manson, “it would be better that they be whole grains, or that they come from fruits, vegetables, and legumes.”
Whole grains are rich in fiber and magnesium, which may explain why people who eat them have a lower risk of diabetes.
Carbs aside, any diet that helps you lose unwanted pounds is your best bet.
“We found reduced fasting insulin—which is a pretty clear indication of improved insulin sensitivity—after weight loss on any of the diets that we studied,” says Sacks. “It’s the reduction in body weight and body fat that decreased insulin levels.”
Sources: Int. J. Obes. 35: 800, 2011; Am. J. Clin. Nutr. 92: 748, 2010; Int. J. Obes. 2014. doi:10.1038/ijo.2014.52; Circulation 127: A016, 2013; Brit. J. Nutr. 104: 125, 2010; J. Nutr. 137: 1401, 2007.