STUDY FINDS "GOOD" CARBS LINKED TO LOWER BODY WEIGHT

Researchers analyzed dietary habits of 572 people over five years and found those who ate carbohydrates with lower glycemic index values weighed less.

February 8, 2005

WORCESTER, Mass.— Seeking some clarity in the “low carb, no carb” diet craze that has swept the nation in recent years, researchers at the University of Massachusetts Medical School (UMMS) analyzed the eating habits of 572 people in Central Massachusetts and found a clear link between the intake of certain carbohydrate foods and higher body mass index (BMI)— the standard measure for obesity.

The results of the study, published in the current issue (Feb. 15) of the American Journal of Epidemiology, show that people who ate more refined grains, starchy vegetables, white flour and similar carbohydrates were significantly heavier than people who ate foods with “good carbohydrates” such as whole grains, non-starchy vegetables, nuts and seeds. It wasn’t the total amount of carbohydrates that made the difference, it was the type of carbohydrates eaten that tipped the scales. “There are many factors involved in obesity, but our study found a clear association with eating certain carbohydrates and body weight,” said Yunsheng Ma, MD, PhD, assistant professor of medicine at UMMS, and lead author of the study.

Dr. Ma’s team analyzed data collected from 572 people in Worcester County from 1994 to 1998, as part of a National Institutes of Heath-funded blood cholesterol study conducted by Ira S. Ockene, MD, the David J. and Barbara D. Milliken Professor of Preventive Cardiology and professor of medicine at UMMS. Each subject was followed for one year, with his or her eating patterns charted at five different times during that year. Ma’s team also examined the physical activity of the subjects to control for the variables of exercise and energy consumption, thereby focusing the analysis solely on the connection between eating various food containing carbohydrates and body weight.

The carbohydrates were classified based on their glycemic index (GI) which is a measure of how much and how fast a food raises a person’s blood sugar level. Foods with a high GI value rapidly spike blood sugar, while foods with a low GI value can help control blood sugar levels. Several other studies have shown that blood sugar levels are related to fat deposition in tissues because, when blood sugar spikes, insulin is elevated and that prompts the body’s fat and muscle cells to absorb the sugar in the blood and store it as fat.

Carbohydrates are the foods that most severely affect the GI of a person’s diet. Items like potatoes, refined grains, pasta, overly processed breads, starchy vegetables and ingredients such as refined sugars and flour, have the highest GI values. For example, a baked potato has a GI of 85 and an ear of corn’s GI is 60. Other carbohydrates such as whole grains, nuts, many fruits and most vegetables, have lower GI values. A cup of broccoli, for example, has a GI of 0.

Based on the population in Dr. Ma’s study, people weighed 9.6 pounds less for every 10-point reduction in the combined glycemic index of their diet. In other words, a person with a GI of 95 typically weighed nearly 10 pounds more than someone in the study with a GI of 85, all other factors being equal. “Nearly 10 pounds is a clinically significant difference,” said Barbara Olendzki, RD, MPH, an instructor in medicine at UMMS and a co-author of the study. “One of the takeaway messages of these findings is that if people can lower the GI of their diet by choosing the best carbohydrates to eat, they should be able to lose some weight. Those lower GI foods can also be helpful for appetite control.”

Recent national studies have shown that the number of Americans who are obese has jumped 61% since 1991. Today, some two-thirds of Americans are overweight (BMI of 25 to 30), with nearly 30 percent of the country’s adult population now considered obese. The rise in obesity is believed to be a key factor in the dramatic increase in type 2 diabetes in the United States. During the same time frame, several studies have documented a significant drop in the overall fat content of the American diet. That data, coupled with the findings published this month from Dr. Ma’s study, suggest that it is the type of carbohydrate in a person’s diet, along with proper exercise and overall caloric intake, that is most relevant in affecting body weight. “We must continue to examine all the factors that play a role in obesity. In the meantime I hope these findings will help people make better choices in their diet and help those who are motivated, to lose weight and improve their quality of life,” Dr. Ma said.

The University of Massachusetts Medical School, one of the fastest growing academic health centers in the country, has built a reputation as a world-class research institution, consistently producing noteworthy advances in clinical and basic research. TheMedical School attracts more than $167 million in research funding annually, 80 percent of which comes from federal funding sources. UMMS is the academic partner of UMass Memorial Health Care, the largest health care provider in Central Massachusetts. For more information visit www.umassmed.edu

Contact: Michael Cohen 508-856-2000, michael.cohen@umassmed.edu