A few years ago, Dr Richard Kahn, the now-retired chief scientific and medical officer of the American Diabetes Association, was charged with organising 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, it is weak,” Kahn said in a recent interview.
Studies tended to be short term, diets unsustainable, differences among them clinically insignificant. The only thing that seemed to help people with diabetes was weight loss and for weight loss, there is no magic diet.
But people want diet advice and Kahn reasoned the association should say something about diets. So, like the National Institutes of Health, it went with the US Department of Agriculture’s food pyramid.
Why? “It’s a diet for all America,” 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 programme at the Joslin Diabetes Center at Harvard Medical School.
Limit carbs
There is a diet that helps with diabetes, the two doctors said: one that restricts or 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,” Hallberg says 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 also the medical director of a start-up developing nutrition-based medical interventions.
But there are no large and rigorous studies showing low-carb diets offer an advantage. There is not even a consensus on the definition of a low-carb diet. “There have been debates for the history of diabetes about which kind of diet is best,” says Dr C. Ronald Kahn, Chief Academic Officer at Joslin, and no relation to Richard Kahn. But, he says, “the answer isn’t so straightforward.” In support of a diet like 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 centre 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 per cent with the very low carb diet, meaning that much less insulin was required to maintain normal blood glucose levels.
“Since diabetes results when the body can’t produce enough insulin, perhaps it is a good idea to reduce the amount of insulin it needs by eating very low carbohydrate diets,” Hall says.
Some longer-term studies, though, failed to show that low-carb diets benefited glucose control. Even if diets are effective in the short term, Hall says, “the difficulty is adhering to it over the long term”.
Good overall health?
Another issue with low-carb diets, researchers say, is what will happen to overall health if diabetics follow the diet for decades. (Heart attacks are the major killer of people with diabetes.) Insulin levels may be better, but, says Dr Rudolph Leibel, Co-director of Columbia University’s Naomi Berrie Diabetes Center, “effects of a low-carbohydrate diet on lipoproteins and vascular biology could offset such a ‘benefit’.” That is it is not clear if a lower insulin level would translate into fewer heart attacks.
Hamdy, whose recommended low-carbohydrate diet is less restrictive than the one Hallberg suggests, reports that many patients in his clinic have been able to stay with the diet for as long as five years, losing weight and keeping it off. His study involved 129 patients, half of whom were able to lose weight and keep it off, and those who did maintained an average weight loss of 9.5 per cent. Their diabetes was much improved.
But multiple studies have found that when it comes to weight loss — the only proven way to help with blood sugar control over the long term — there is no difference among diets that restrict calories, fat or carbohydrates.
— New York Times News Service
