Dieting Slims Waistline But Not Abdominal Fat Cells

WINSTON-SALEM, N.C., Aug. 8 -- The waistline may succumb to a diet, but it takes exercise as well to shrink the size of subcutaneous abdominal fat cells that affect type 2 diabetes, according to researchers here.

The larger subcutaneous abdominal fat cells are, the more likely the development of type 2 diabetes, independent of obesity and insulin resistance, said Tongjian You, Ph.D., and colleagues, of Wake Forest School of Medicine here.

Previous studies have also shown that obese women with larger subcutaneous abdominal fat cells are more likely to have hyperinsulinemia and glucose intolerance, Dr. You and colleagues said in the August issue of the International Journal of Obesity.

The current study included 45 obese, middle-age women (average age: 58). They were randomized to one of three groups. The first group was put on a diet to reduce their energy intake by 2,800 calories per week. The second group was put on a diet plus a regimen of treadmill walking at a moderate pace (one to two miles per hour) three times weekly. The third group was put on a diet plus more-intense exercise (three to four miles per hour on a treadmill) three times a week.

In the two exercise groups, the combination of dieting plus exercise was designed to achieve a weekly energy deficit of 2,800 calories.

At 20 weeks, all three groups had lost a comparable amount of weight. The diet-only group averaged a 10.4 kg loss, the diet plus moderate exercise group 10.9 kg, and the diet plus intense exercise group 8.8 kg. The latter group maintained more lean tissue and therefore lost slightly less weight.

All groups reduced their waist size by a similar amount. The diet only group slimmed by an average of 8.8 cm, the diet plus moderate exercise group 9.4 cm, and the diet plus intense exercise group 9.3 cm (P=not significant).

However, analysis of biopsied subcutaneous abdominal fat cells revealed that while the cells of the diet-only group shrank by an average of 0.8%, those of the moderate exercise group shrank by about 18% and those of the intense exercise group by nearly 17% (P<.05 for both compared with the diet group). The difference was not significant between the exercise groups.

Previous research suggested that exercise preferentially mobilizes lipids from the abdominal region as opposed to other areas of the body. This mobilization is likely mediated by a decrease in hormone-sensitive lipase enzyme activity and an increase in lipoprotein lipase enzyme activity, the researchers noted.

The weight loss and waist reduction in the diet-only group likely resulted from shrinking visceral and intramuscular fat cells in the abdomen, rather than subcutaneous abdominal fat cells, although the study did not directly examine these others types of fat cells, Dr. You said in an interview.

However, because of the study's small sample size, there may have been significant reductions in the size of subcutaneous abdominal fat cells in the diet-only group that went undetected, he added.

If confirmed by larger studies, "these findings suggest that exercise is important to reducing the size of these cells and might one day be part of a prescription for treating the health complications associated with abdominal fat," Dr. You said.