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Obesity and low muscle mass join to impact body function

OW Staff | 3/7/2012, 5 p.m.

Obesity appears to increase muscle wasting by increasing insulin resistance and decreasing glucose absorption, which is important for creating muscles and supplying energy.

Older people who are obese and have low muscle mass are more susceptible to physical functioning problems in their everyday life, whether it is standing up or walking around, according to a recent USC study published in the journal Obesity.

The effect of the combination of increased weight and decreased--muscle was much greater than either problem alone-physical functioning problems were 91 percent higher for obese people with low muscle mass compared to those with just obesity.

Still in the end, the culprit appears to be obesity and the lack of muscle mass a side effect, say the authors, USC Davis School of Gerontology professor Eileen Crimmins and USC doctoral student Morgan Canon.

The association between body composition and functioning appears to be related to insulin resistance, often a factor in diabetes. Obesity-caused insulin resistance affects glucose absorption, an important ingredient for creating muscles and supplying energy. Obese subjects with low muscle mass had about 35 per higher levels of insulin resistance than obese subjects with normal muscle mass, the study found.

Further, the extra weight also creates added strains on muscles and joints, potentially causing aches and pains. This can lead to a more sedentary lifestyle and a lack of the everyday exercise that build muscles.

"As people age, muscle wasting may increase disability for those gaining weight earlier in life," said Canon, the lead author. "If we understand the mechanisms behind this, we may be able to intervene earlier. We can change the trajectory."

This cross-sectional study surveyed 2,287 people age 60 and older without diagnosed diabetes. Insulin resistance was measured using the homeostasis model assessment and inflammatory states were assessed through measurement of serum C-reactive protein.

Physical functioning was measured though simple tasks, such as walking up 10 steps, stooping, crouching and kneeling, standing for long periods of time or carrying a heavy object.

As the population ages and people live longer, "successful aging"--the capacity to maintain quality of life and independence for those over 65--is important to understand as the answers impact the effectiveness and the cost of healthcare.

The authors emphasize the importance of maintaining a healthy weight and lifestyle in early life and mid-life. However, even older obese adults may benefit by keeping blood sugar levels in an optimal range and losing weight, particularly in their midsection. At the same time, weight loss should be accompanied by strength-building exercises to ensure muscle isn't being lost along with fat.