Published: Sept. 14, 2005
Updated: Sept. 15, 2005
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By Duke Medicine News and Communications
DURHAM, N.C. -- Inactivity leads to significant increases in visceral fat, and a moderate exercise regimen can keep this potentially dangerous form of fat at bay, according to the results of the first randomized clinical trial evaluating the effects of exercise amount and intensity in sedentary overweight men and women.
Additionally, the Duke University Medical Center researchers found that increasing amounts of exercise can reduce visceral fat. In terms of overall weight gain, the patients who did not exercise would gain approximately four pounds per year, the researchers said.
Visceral fat, the form which accumulates around the organs inside the belly, particularly concerns physicians because increased levels have been associated with insulin resistance, cardiovascular disease and other metabolic syndromes. Visceral fat is located deeper in the body than subcutaneous fat, which lies just under the skin.
"In our study, the control group that did not exercise saw a sizable and significant 8.6 percent increase in visceral fat in only six months," said Duke exercise physiologist Cris Slentz, Ph.D., lead author of a study published in the October issue of the Journal of Applied Physiology. "We also found that a modest exercise program equivalent to a brisk 30-minute walk six times a week can prevent accumulation of visceral fat, while even more exercise can actually reverse the amount of visceral fat.
"We believe that these results shine a clear spotlight on the high costs Americans are paying for their continued inactivity," Slentz continued. "I don't believe that people in general have gotten lazier – it's more that they are working too hard or are at their desks working on computers with fewer opportunities for exercise. The situation is out of balance."
The modest exercise program cited by Slentz is consistent with the latest recommendations by the Centers for Disease Control and Prevention and the American College of Sports Medicine. However, Slentz believes that the public health message needs to be modified, especially for a country where two out of three adults are overweight or obese.
"Until we are able to prevent the weight many dieters regain following short-term dieting success, we should place a greater national emphasis toward prevention," Slentz said. "It will be a challenge to change the message from 'exercise now to lose weight' to 'exercise now so in five years you won't be 20 pounds heavier.'"
To better understand the effects of differing amounts of exercise, the researchers studied 175 overweight sedentary men and women who were beginning to show signs of lipid problems. They were randomized into one of four groups: no exercise, low dose/moderate intensity (equivalent of 12 miles of walking per week), low dose/vigorous intensity (12 miles of jogging per week) or high dose/vigorous intensity (20 miles of jogging per week).
Since the trial was designed solely to better understand the role of exercise, patients were told not to alter their diet during the course of the trial, which lasted six months for the group that did not exercise or eight-months for the exercise groups. The additional two months for the exercise group came at the beginning of trial, when participants slowly ramped up their exercise to their designated levels.
The exercise was carried out on treadmills, elliptical trainers or cycle ergometers in a supervised setting. The researchers used computed tomography (CT) both before the exercise program began and eight months later to determine the extent and distribution of fat change.
"There were no significant changes in visceral, subcutaneous or total fat in either of the low exercise groups for men or women, which suggest that this amount of exercise is adequate to prevent significant gain in fat around the stomach, and that the amount of exercise is more important than the intensity," Slentz said.
"On the other hand, participants who exercised at a level equivalent to 17 miles of jogging each week saw significant declines in visceral fat, subcutaneous abdominal fat and total abdominal fat," Slentz continued. "While this may seem like a lot of exercise, our previously sedentary and overweight subjects were quite capable of doing this amount."
Specifically, those participants exercising at the highest level saw a 6.9 percent decrease in visceral fat and a 7 percent decrease in subcutaneous fat.
The Duke team was led by cardiologist William Kraus, M.D., who received a $4.3 million grant from the National Heart, Lung and Blood Institute in 1998 to investigate the effects of exercise on sedentary overweight adults at risk for developing heart disease and/or diabetes. The results of that five-year trial, known as STRRIDE (Studies of Targeted Risk Reduction Interventions through Defined Exercise), and other analyses of the data collected, began to be published in 2002.
The Duke team is currently enrolling patients in STRRIDE II, in which researchers are seeking to determine the effects of weight training, alone and in combination with aerobic training, on cardiovascular health.
Joining Slentz and Kraus were Duke colleagues, Lori Aiken, Connie Bales, Ph.D., Johanna Johnson, and Brian Duscha. Joseph Houmard, Ph.D., and Charles Tanner from East Carolina University, were also members of the team.