Study Title:

Aerobic Exercise and Belly Fat

Study Abstract

Adipose tissue inflammation causes metabolic disturbances, including insulin resistance and hepatic steatosis. Exercise training (EX) may decrease adipose tissue inflammation, thereby ameliorating such disturbances, even in the absence of fat loss. The purpose of this study was to 1) compare the effects of low-fat diet (LFD), EX, and their combination on inflammation, insulin resistance, and hepatic steatosis in high-fat diet-induced obese mice and 2) determine the effect of intervention duration (i.e., 6 vs. 12 wk). C57BL/6 mice (n = 109) fed a 45% fat diet (HFD) for 6 wk were randomly assigned to an EX (treadmill: 5 days/wk, 6 or 12 wk, 40 min/day, 65–70% O2max) or sedentary (SED) group. Mice remained on HFD or were placed on a 10% fat diet (LFD) for 6 or 12 wk. Following interventions, fat pads were weighed and expressed relative to body weight; hepatic steatosis was assessed by total liver triglyceride and insulin resistance by HOMA-IR and glucose AUC. RT-PCR was used to determine adipose gene expression of MCP-1, F4/80, TNF-, and leptin. By 12 wk, MCP-1, F4/80, and TNF- mRNA were reduced by EX and LFD. Exercise (P = 0.02), adiposity (P = 0.03), and adipose F4/80 (P = 0.02) predicted reductions in HOMA-IR (r2 = 0.75, P < 0.001), only adiposity (P = 0.04) predicted improvements in hepatic steatosis (r2 = 0.51, P < 0.001). Compared with LFD, EX attenuated increases in adiposity, hepatic steatosis, and adipose MCP-1 expression from 6 to 12 wk. There are unique metabolic consequences of a sedentary lifestyle and HFD that are most evident long term, highlighting the importance of both EX and LFD in preventing obesity-related metabolic disturbances.

From press release:

A new University of Illinois study suggests that moderate amounts of exercise alone can reduce the inflammation in visceral fat—belly fat, if you will—that has been linked with metabolic syndrome, a group of risk factors that predict heart disease and Type 2 diabetes.

"In the study, the benefits of exercise were apparent, even without a change in diet. We saw improvements in insulin sensitivity, less fat in the liver, and less inflammation in belly fat," said Jeffrey Woods, a U of I professor of kinesiology and community health and faculty member in the U of I Division of Nutritional Sciences and the Integrative Immunology and Behavior Program.

Belly fat is particularly dangerous because it produces inflammatory molecules that enter the bloodstream and increase the risk of heart disease and diabetes, he said.

"Scientists now know that obesity is associated with a low-grade systemic inflammation. Obese people have higher levels of circulating inflammatory markers, such as C-reactive protein (CRP), which are produced and secreted by fat tissue. This inflammation then triggers the systemic diseases linked with metabolic syndrome, such as Type 2 diabetes and heart disease," he said.

In the study, Woods and his colleagues examined the effects of diet and exercise on the inflammation of visceral fat tissue in mice. A high-fat diet was first used to induce obesity in the animals. After 6 weeks, mice were assigned to either a sedentary group, an exercise group, a low-fat diet group, or a group that combined a low-fat diet with exercise for 6 or 12 weeks so the scientists could compare the effects in both the short and long term.

"The surprise was that the combination of diet and exercise didn't yield dramatically different and better results than diet or exercise alone," said Vicki Vieira, the lead author of the study.

"Unexpectedly, the only significant increase from 6 to 12 weeks in belly fat—the type of fat that triggers these inflammatory diseases--was in the mice who were sedentary, which suggests that exercise is an effective behavioral approach to reduce the accumulation of visceral fat even when fat in the diet is high," she said.

Woods says that is a promising finding. "The benefits of exercise were apparent even if the animals were still eating a high-fat diet. That tells me that exercise could decrease or prevent these life-threatening diseases by reducing inflammation even when obesity is still present."

"The good news is that this was a very modest exercise program. The mice ran on a treadmill only about one-fourth of a mile five days a week. For humans, that would probably translate into walking 30 to 45 minutes a day five days a week," he noted.

"Even if you struggle with dieting, we believe you can still reduce the likelihood of developing obesity-related inflammatory diseases, such as Type 2 diabetes and heart disease, by adding a modest amount of exercise to your life," said Woods.

These results were reinforced by the scientists' study of sedentary older adults published in a recent issue of Brain, Behavior and Immunity (BBI).

In that 10-month study, one group of sedentary older adults participated in three 45- to 60-minute cardiovascular exercise sessions per week, while another group focused on exercises to improve non-cardiovascular flexibility and balance for 75 minutes twice a week.

"At the end of the study, the 'cardio' group had lower levels of C-reactive protein (CRP), less belly fat, and improved general fitness than the 'flex' group," said Ph.D. candidate Vieira.

"The lower CRP levels were partially mediated by the reduction in trunk fat," she explained.

Study Information

Victoria J. Vieira, Rudy J. Valentine, Kenneth R. Wilund, Nirav Antao, Tracy Baynard, and Jeffrey A. Woods
Effects of exercise and low-fat diet on adipose tissue inflammation and metabolic complications in obese mice
Am J Physiol Endocrinol Metab
2009 May
Univ. of Illinois at Urbana-Champaign

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