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.
“As people age, muscle wasting may increase disability for those gaining weight earlier in life,” said the study’s lead author.
In the end, the culprit appears to be obesity and the lack of muscle mass is a side effect, said USC Davis School of Gerontology professor Eileen Crimmins and USC doctoral student Morgan Canon, the study’s authors.
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 factor for creating muscles and supplying energy. Obese people with low muscle mass had nearly 35 percent higher levels of insulin resistance than obese subjects with normal muscle mass, the study found.
Moreover, 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 who were 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 because the answers have an impact on the effectiveness and cost of health care.
The authors emphasized the importance of maintaining a healthy weight and lifestyle in early 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 mid-section. Nevertheless, weight loss should be accompanied by strength-building exercises to ensure that muscle isn’t being lost along with fat.
The study was funded by a training grant from the National Institute on Aging and USC Davis.