A few years ago, Richard Kahn, the now-retired chief scientific and medical officer of the American Diabetes Association, was charged with organizing a committee to prescribe a diet plan for people with diabetes. He began by looking at the evidence for different diets, asking which, if any, best controlled diabetes.
“When you look at the literature, whoa is it weak. It is so weak,” Dr. Kahn said in a recent interview.
Studies tended to be short term, diets unsustainable, differences among them clinically insignificant. The only thing that really seemed to help people with diabetes was weight loss — and for weight loss, there is no magic diet.
But people want diet advice, Dr. Kahn reasoned, and the association really should say something about diets. So it, like the National Institutes of Health, went with the Department of Agriculture’s food pyramid.
Why? “It’s a diet for all America,” Dr. Kahn said. “It has lots of fruits and vegetables and a reasonable amount of fat.”
That advice, though, recently came under attack in a New York Times commentary written by Sarah Hallberg, an osteopath at a weight loss clinic in Indiana, and Osama Hamdy, the medical director of the obesity weight loss program at the Joslin Diabetes Center at Harvard Medical School.
There is a diet that helps with diabetes, the two doctors said: one that restricts — or, according to Dr. Hallberg, severely restricts — carbohydrates.
“If the goal is to get patients off their medications, including insulin, and resolve rather than just control their diabetes, significant carb restriction is by far the best nutrition plan,” Dr. Hallberg said in an email. “This would include elimination of grains, potatoes and sugars and all processed foods. There is a significant and ever growing body of literature that supports this method.” She is in private practice at Indiana University Health Arnett Hospital and is medical director of a start-up developing nutrition-based medical interventions.
But there are no large and rigorous studies showing that low-carbohydrate diets offer an advantage, and, in fact, there is not even a consensus on the definition of a low-carbohydrate diet — it can vary from doctor to doctor.
“There have been debates for literally the whole history of diabetes about which kind of diet is best,” said Dr. C. Ronald Kahn, chief academic officer at Joslin, and no relation to Dr. Richard Kahn. But, he said, “the answer isn’t so straightforward.”
In support of a diet like Dr. Hallberg’s, there is one recent short-term study, by Kevin Hall of the National Institute of Diabetes and Digestive and Kidney Diseases and his colleagues, involving 17 overweight and obese men, none of whom had diabetes. They stayed in a clinical center where they ate carefully controlled diets. The researchers asked what would happen if calories were kept constant but the carbohydrate composition of a diet varied from high to very low. The answer was that insulin secretion dropped 50 percent with the very low carbohydrate diet, meaning that much less insulin was required to maintain normal blood glucose levels.
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