Although weight-loss therapy is recommended to improve obesity-related medical complications and functional impairments (2
), a prevailing concern in the therapy of obese older adults is that weight loss alone will accelerate sarcopenia. However, the precise amount of muscle loss that result from voluntary weight loss in obese older adults and the efficacy of exercise in protecting against this weight-loss-induced reduction in muscle mass in this population are unclear. Therefore, we used a randomized trial to directly compare the effects of diet alone versus diet + exercise on changes in total FFM, appendicular UE and LE lean mass, and UE and LE muscle strength in obese older adults. Our data show that diet only reduces FFM by ~3.5 kg, which corresponds to a loss of appendicular lean mass of ~2.5 kg. These losses of lean tissue are effectively reduced (by one-half) through an exercise program that incorporates PRT. In fact, the loss of UE lean mass is completely prevented by regular exercise. Although the loss of LE lean mass is not completely prevented, exercise still increases LE muscle strength (despite lower muscle mass after weight loss). The volume of exercise training correlates with the amount of UE and LE lean mass, suggesting a dose response to resistance exercise training. These findings demonstrate that weight-loss-induced loss of FFM can be attenuated or prevented by regular exercise, which additionally leads to significant gains in UE and LE muscle function.
The 3.5 ± 2.1 kg (5.9%) loss of FFM that we observed in obese older adults consisted of 32% of the total absolute ~11 kg weight loss over the 6-month study interval. Data from previous weight-loss studies that were conducted in young and middle-aged adults found 2.5–2.8 kg loss of FFM with a weight loss of ~10 kg (4
). Importantly, we also found that the addition of exercise to diet reduced the FFM loss from 3.5 to 1.8 kg in older adults. Previous weight-loss studies conducted in younger adults reported that exercise combined with diet reduced the expected FFM loss to 1.7 kg (10
). Therefore, the present data further demonstrate that regular exercise added to diet is just as effective in attenuating FFM loss in older adults despite the presence of underlying age-related sarcopenia.
Older adults are particularly susceptible to the adverse effects of excessive body weight on physical function due to 1) the decreased muscle mass and strength that occur with aging and 2) a need to carry greater weight due to obesity (30
). Indeed, obese older adults have been shown to have sarcopenia (low relative muscle mass, low muscle strength per muscle mass) despite more than adequate body weight which is opposite the stereotypical frail older adult (30
). In the present study, we found that relative FFM (the percent of body weight as FFM) improved in the diet group and the diet + exercise group, but the improvement was greater in the diet + exercise group due to the additional exercise-induced preservation of FFM. In addition, we found that muscle quality (muscle strength per muscle mass) (21
) improved in both groups, but the improvement was also greater in the diet + exercise group due to the additional exercise-induced increase in muscle strength. Because muscle strength increased whereas muscle mass decreased, the improvement in muscle quality in the diet + exercise group could best be explained by exercise-induced neuromuscular activation (22
). Additional mechanisms for the improvement in muscle quality observed in the diet + exercise group are possible and may include improvement in muscle architecture (16
) and fiber type area (20
) and increase in high-energy phosphate availability (15
). The reason for the improvement in muscle quality in the diet group is unknown. However, both obesity and aging are accompanied by increased muscle lipid content, which correlates with decreased muscle strength (11
), and weight loss decreases muscle fat infiltration (12
). Therefore, muscle quality may improve due to a decrease in muscle fat infiltration as well as a reduction in inflammation (27
) as a result of weight loss. Indeed, there is an association between inflammation and muscle mass and strength (8
), and thus it is possible that a loss of muscle fat may benefit through a decrease in inflammation (28
). Our findings are consistent with a recent report by Wang et al. (36
) that knee strength was maintained and muscle quality was improved despite 3 kg FFM loss during weight loss in obese older adults. However, although our data demonstrate that 6 months of diet alone does not decrease muscle strength despite muscle loss, they also demonstrate that the addition of an exercise program is essential for inducing significant increases in muscle strength, thus potentially improving overall function in frail obese older adults (9
A primary goal of our study was to determine the efficacy of an exercise program to minimize the loss of lean tissue during voluntary weight loss. Therefore, because the adaptations to exercise are muscle specific and overload dependent, we incorporated different resistance exercises that stimulated major muscle groups of the UE and the LE and progressively increased the exercise-training volumes (1
). In response to exercise added to diet, we found no loss of lean mass in the UE, whereas the loss of lean mass in the LE was reduced by ~50%. To our knowledge, this is the first study to report a differential protective effect of exercise in the UE and the LE extremities in older adults during voluntary weight loss. As the quantity and the quality of UE and LE exercises were similar, a possible explanation for this finding is that the UE may be more responsive to acute high-intensity PRT because it is more novel, whereas the weight-bearing LE may be used more often during daily activities (e.g., walking and stair climbing) in community-living obese adults. Regardless of the amount of muscle mass lost, we found that the addition of exercise to dietary restriction significantly improved muscle strength in both UE and LE.
Our study is the first direct comparison between a diet alone group and a diet + exercise group within a randomized clinical trial specifically conducted in frail obese older adults. We used PRT following ACSM guidelines (18
) supervised by a physical therapist at our exercise facility to ensure safe and effective implementation of the exercise regimen. Although a few participants were unable to complete some exercises due to site-specific orthopedic or arthritic impairments expected in this frail population, overall, the compliance was high and all participants completed the 72 sessions of exercise intervention. A limitation of our study is that we did not have a control group that did not participate in weight loss or a group that participated in exercise only. These groups are essential for future research to understand how weight loss may affect FFM in this population and how resistance exercise may assist in preserving FFM. Another limitation of our study is that we were not able to examine sex differences in response to diet and exercise due to the small sample size. However, we controlled for the effect of sex by including it as a covariate in the analyses of variance. In addition, our study was limited to 6-month duration, so longer studies are needed to evaluate long-term compliance with diet and exercise in this older population.
In conclusion, our study provides evidence that the addition of exercise training to diet reduces the amount of muscle mass loss during voluntary weight loss in frail obese older adults and significantly increases muscle strength. Therefore, diet should be combined with regular exercise to reduce the loss of FFM in older obese adults undergoing weight-loss therapy to attenuate obesity-related medical and functional complications.