FRIDAY, July 20, 2007 (HealthDay News) -- A low-carbohydrate diet helps people with a condition called metabolic syndrome, a collection of serious risk factors found in some obese individuals.
Now, a new study confirms the diet is effective against the syndrome, and the researchers think they've discovered how it works.
Eating a low-carb diet improves the hormonal signaling involved in obesity and improves the sense of fullness, allowing weight loss, according to study leader Matthew R. Hayes, a postdoctoral fellow at the University of Pennsylvania.
"There is this strong interest in the field in carb-restricted diets in the treatment of obesity," said Hayes, who conducted the research while a doctoral student at Pennsylvania State University. "That [interest] comes from a number of controlled clinical trials that demonstrate overweight or obese people, maintained on low-carb diets, are successful if they adhere to the diet."
"It's definitely a hot debate in the field," Hayes added, whether the diets work. "We wanted to look at not only if it worked but how."
People with metabolic syndrome struggle with excessive abdominal fat; low levels of HDL -- good -- cholesterol; and insulin resistance or glucose intolerance, in which the body doesn't properly use insulin or blood sugar. Metabolic syndrome raises the risk of heart disease, type 2 diabetes and other serious health problems, according to the American Heart Association.
Hayes and his colleagues studied 20 men and women with metabolic syndrome, instructing them to follow a low-carb diet similar to the popular South Beach Diet. For phase one, which lasted two weeks, the study participants were told to get 10 percent of their calories from carbohydrates. For phase 2, which lasted the remaining 10 weeks of the study, they were told to eat up to 27 percent carbs.
"The subjects did lose weight, and they lost total body fat. Their weight was a little over 200 pounds when the study started. By the end of the study, the subjects weighed about 193, 194. They lost close to 10 pounds during the three-month study."
And, Hayes said, "By the end of the study, about 50 percent no longer had metabolic syndrome."
The study participants didn't follow the diets strictly, he found. "Phase one intake was 25 percent [carbohydrates], on average," he said, rather than the 10 percent recommended. "Phase two carb intake was 35 percent," he said, although 27 percent was recommended. But it was a reduction from the participants' pre-study diet, which included 47 percent of calories from carbohydrates, he said.
To find out why the weight declined, Hayes' team did hormone assays, measuring fasting and post-meal blood levels of hormones associated with appetite and food intake, such as insulin, leptin and cholecystokinin (CCK).
"We found some changes in hormone levels," he said. "We saw a decrease in insulin, a decrease in leptin levels by the end of phase one. It was fast."
"By the end of phase 2, the insulin levels had crept up toward baseline; the leptin levels also rose, but it did not come back to the levels at baseline," Hayes said.
"These alternations in hormone levels acting together help reduce the amount of food consumed," he said. "There's a synergy. Based on the literature already out there, we are speculating that this synergy of hormones may be the mechanism explaining why people are satisfied with less food and [the low-carb diet] results in weight loss."
However, Hayes emphasized that the study, published in the August issue of The Journal of Nutrition, was small and preliminary, and more research is needed.
Connie Diekman, director of university nutrition at Washington University in St. Louis and president of the American Dietetic Association, also urged caution when interpreting the study findings. "The study is small in size, and the population is not extremely diverse," she said, although she thinks the study design was good.
"The study was focused on metabolic syndrome, so the outcomes may not be transferable to people who are overweight but do not have the syndrome, since the cause of the syndrome is still not clear," Diekman said.
To learn more about metabolic syndrome, visit the American Heart Association.
SOURCES: Matthew R. Hayes, Ph.D., postdoctoral fellow, University of Pennsylvania, Philadelphia; Connie Diekman, M.Ed., R.D., director of university nutrition, Washington University, St. Louis, and president, American Dietetic Association; August 2007, The Journal of Nutrition
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