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Study: Insulin Levels Show Who May Benefit from Carb-Cutting

Summary of Study from May 2007 in JAMA

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Updated August 30, 2007

I hope the days of recommending essentially the same diet for everyone ends soon. Studies such as this one should help.

This study of obese young adults, similar to the one I reported on in late 2005, attempts to differentiate which people would do better on different diets. One of the two diet groups was a traditional low fat diet with 55% of the calories from carbohydrate. The other group ate a moderate carb diet with 40% of calories from carbohydrate, with a focus on "good carbs" - those with a lower glycemic load. The diets of both groups were 25% protein, which is somewhat above the usual recommendations.

Capsule Summary of Results

It turned out people with high insulin levels in their blood lost more weight on the diet with more fat and less carbohydrate. People with normal blood insulin lost the same amount on both diets. However, regardless of insulin level, the lower carb group had a greater decrease in triglycerides and a greater increase in HDL ("good cholesterol"), while the LDL ("bad cholesterol") dropped more in the low fat group. LDL particle size was not measured. (Other studies have found that low fat diets tend to decrease LDL at least partly by decreasing the size of the cholesterol particles, however smaller particles are associated with heart disease to a much greater extent than large LDL particles. More on LDL particle size

These changes are consistent with those usually found on low carb diets.

Things to note about the study:

    • There was no group that was really low carb, although the "low glycemic load" group, at 40% carbohydrate, is still lower in carbs than the average diet or the recommended "food pyramid diet". It is consistent with the Zone Diet. Even so, differences were found between the groups.
    • People were instructed to keep to the recommended percentages, and then eat "ad libitum", in other words eat as much as they wanted. This means that there was no one *amount* of carbohydrate, fat, or protein that people were instructed it eat. When they ate more, they ate more carbs.
    • At the end of 18 months, the high insulin women on the lower carb diet lost an average of almost 13 pounds, whereas the high insulin women on the higher carb low carb diet lost an average of 2½ pounds. Predictably, body fat percentage dropped more as well.
    • Figures were not given for the weight loss of the participants with normal insulin levels, only that the amount did not differ between diet groups.
    • None of the young adults in the study were diabetic.

    Reference:

    Ebbeling, Cara, Leidig, Michael, Feldman, Henry, et al. "Effects of a Low–Glycemic Load vs Low-Fat Diet in Obese Young Adults." Journal of the American Medical Association. 297.19 (2007):2092-2102.

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