Insulin may thwart low-fat diet

If your body produces too much insulin, you may be more susceptible to weight gain on a conventional low-fat diet.

Overview

There may be a physiological reason why some people do well on low-fat diets while others fail and it's not a lack of willpower. This research was published in the Journal of the American Medical Association in May 2007.

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Questions and answers

What did this study find?

Dr. Sanjay Gupta, CNN chief medical correspondent: It's a question a lot of us ask: Why do some people succeed on a low-fat diet while others fail miserably? It has nothing to do with willpower or motivation. A study in the Journal of the American Medical Association says that your body's biology may hold the explanation: If your body produces too much insulin, you may be more susceptible to weight gain on a conventional low-fat diet.

What is insulin and what does it have to do with weight gain?

Gupta: Insulin is a hormone that lowers blood sugar and it also tells the body to store fat. It metabolizes carbohydrates and tells the body to store fuel. High-carbohydrate meals can bring spikes in insulin levels, pushing your body into hyper-fuel-storage mode, causing extreme hunger, overeating and weight gain. This cycle of hunger and spiking insulin can make it challenging to keep weight off even with a low-fat diet. But people who were put on a low-glycemic-index diet could overcome that cycle of hunger and weight gain. And they lost more than twice as much weight as people who didn't have the problem with spiking insulin levels.

What is a low glycemic index diet?

Gupta: Seventy-three participants were randomly assigned to one of two diets: low fat or low glycemic index. The two diets, at first glance, aren't extremely different, but the distinctions between them are important. The low-fat diet focuses on whole grains, low fat, veggies and fruits and contains 55 percent carbohydrates and 20 percent fat.

The low-glycemic-index diet has a similar focus on fruits, vegetables and whole grains, but adds nuts, seeds and healthful oils such as olive and canola oil. The percentage of carbohydrates is lower, at 45 percent, and fat is higher at 35 percent. After six months, people on the low-glycemic diet lost twice as much weight as people on the low-fat diet. After 18 months, almost 13 pounds were lost on the low-glycemic-index diet, compared with only 2.6 pounds on the low-fat diet. That's a huge difference.

What are some foods that make sense if you have this tendency to produce too much insulin?

Gupta: The key is to make healthier food selections. Instead of eating foods that digest quickly, like potatoes, white bread and pasta, you want to eat foods that digest slowly: soybeans, oatmeal, broccoli, whole grain breads and some types of fruit.