Diabetes & Byetta

Low-Glycemic Load Diet May Be More Effective For Dieters With Certain
Insulin Response Patterns

May 2007 - Overweight individuals who secrete insulin at a higher level
may experience greater weight loss by selecting a low-glycemic load
diet, compared to a low-fat diet, according to a study in the May 16
issue of JAMA. The researchers also found a low-glycemic load diet to
have beneficial effects on HDL cholesterol and triglyceride concentrations.

"With prevalence approaching one-third of the population, obesity is
among the most important medical problems in the United States and
identification of effective dietary treatment has become a major public
health priority. Three popular diets—low fat, low carbohydrate, and low
glycemic load—have recently received much attention.

However, clinical trials have produced inconsistent findings, with some
suggesting that one diet is superior for weight loss and others
indicating no difference between diets," the authors write. They add
that one explanation for the inconsistent findings could relate to the
inherent physiological differences among study participants. "One
physiological mechanism that might relate weight loss to dietary
composition is individual differences in insulin secretion."

Cara B. Ebbeling, Ph.D., of Children’s Hospital Boston, and colleagues
conducted a study to determine whether insulin secretion affects weight
loss and body fat loss among obese individuals with different diets.
This randomized controlled trial, conducted from September 2004 to
December 2006, included 73 obese young adults (age 18-35 years) and
consisted of a 6-month intensive intervention period and a 12-month
follow-up period.

Serum insulin concentration at 30 minutes after a 75-g dose of oral
glucose was determined at baseline as a measure of insulin secretion.
Outcomes were assessed at 6, 12, and 18 months. Participants consumed
either a low–glycemic load (40 percent carbohydrate and 35 percent fat)
or low-fat (55 percent carbohydrate and 20 percent fat) diet.

The researchers found that change in body weight and body fat percentage
did not differ between the diet groups overall. However, for those with
insulin concentration at 30 minutes above the median (midpoint), the
low–glycemic load diet produced a greater decrease in weight (12.8 lbs.
vs. 2.6 lbs.) and body fat percentage (–2.6 percent vs. –0.9 percent)
than the low-fat diet at 18 months. There were no significant
differences in these end points between diet groups for those with
insulin concentration at 30 minutes below the median level.

Among all the participants in the study, high-density lipoprotein
cholesterol (the "good" cholesterol) and triglyceride concentrations
improved more on the low–glycemic load diet, whereas low-density
lipoprotein cholesterol (the "bad" cholesterol) concentration improved
more on the low-fat diet.

"The main finding of our study is that a simple measure of insulin
secretion predicted weight and body fat loss on low–glycemic load and
low-fat diets," the authors write. "For obese individuals with high
insulin concentration at 30 minutes during an oral glucose tolerance
test, a low–glycemic load diet may promote more weight and body fat loss
than a low-fat diet.

Regardless of insulin secretion, a low–glycemic load diet has beneficial
effects on concentrations of HDL cholesterol and triglycerides but not
on LDL cholesterol. Additional research is needed to examine these
effects in other populations and to explore the mechanistic basis for
the observed diet-phenotype interaction."

JAMA. 2007;297:2092-2102.

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