Effects of an Individualized Dietary Behavioural Change (IDBC) Programme and Exercise Training in Combination or Separately on Managing Sarcopenic Obesity in Community-dwelling Older Adults: A Cluster Randomized Controlled Trial

Low muscle mass and high body fat mass often coexist in older adults, a condition known as sarcopenic obesity. Older adults with low muscle mass and strength are 1.95-2.62 times more likely to suffer from obesity than those with normal muscle mass. This is because both sarcopenia and obesity have common risk factors that include unhealthy lifestyles and age-related physiological changes with a decline in growth hormones, increased insulin resistance, and increased oxidative stress. Sarcopenic obesity has synergistic detrimental effects on physical functions and overall health. The risks of developing cardio-metabolic diseases, institutionalization, and mortality are higher than with sarcopenia or obesity alone. Depending on the diagnostic criteria, its prevalence can be up to 20.4% and 27.0% in women and men, respectively, in China and worldwide.

Effective interventions to simultaneously increase muscle mass and decrease body fat mass are challenging, but highly warranted. To date, only a limited number of trials have focused on managing sarcopenic obesity. The common proposed interventions are lifestyle interventions (i.e. exercise and a nutritional intervention). Unfortunately, evidence-based interventions are yet to be established due to diverse methodologies with inconsistent results in different clinical trials.

Exercise-based interventions: The current evidence shows that managing sarcopenic obesity with exercise interventions tends to produce better outcomes than with nutritional interventions. A recent systematic review of 15 trials with 856 participants revealed that the combination of aerobic and resistance exercise decreased fat mass and improved physical performance (i.e. gait speed). However, additional benefits could not be observed when combining a nutritional intervention and exercise. Another systematic review of eight RCTs with 605 participants observed that resistance training alone could increase muscle strength. To also improve physical functions (i.e. gait speed and grip strength), exercise combining aerobic and resistance training with dietary supplements seems to have more promising results. Another systematic review of seven RCTs with 558 participants also reported that exercise alone or combined with dietary supplements showed beneficial effects on increasing muscle mass and physical functions in this population. In summary, exercise, especially the combination of resistance and aerobic training, improves body composition and physical performance in older adults with sarcopenic obesity. However, the additional beneficial effects of combining exercise and nutritional interventions were inconsistent.

Nutrition-based interventions: However, nutritional intervention should not be ignored in managing sarcopenic obesity, as unhealthy diet habit is a key factor to develop both sarcopenia (i.e. a result of an inadequate protein intake) and obesity (i.e. a result of an excess calories consumption). Studies suggest that adequate protein intake is essential for building muscles, whereas caloric restriction effectively reduces fat mass. Several studies demonstrated that a hypocaloric diet was effective in reducing fat mass in older adults with sarcopenic obesity. However, this fat mass loss is often accompanied with muscle mass loss. Therefore, a weight loss diet in this population should also focus on preserving muscle mass. Protein, particularly animal-based protein, which contains leucine, can prevent loss of muscle mass associated with weight reduction and maintain physical performance. Although dietary supplements are commonly used to increase protein intake, their effects on sarcopenic obesity remain inconsistent. Protein supplements may cause side effects, including dehydration, liver and renal damage, bloating, and calcium loss. Investigators argue that people should not only take dietary supplements but foods and meals containing a whole range of interacting constituents, which is also one of the points emphasized in the Dietary Guidelines for Americans, 2020-2025. Therefore, investigators believe that modifying the daily diet habits of people with sarcopenic obesity is more appropriate and may produce long-term benefits than solely giving them dietary supplements.

To date, only two intervention studies have attempted to modify the dietary habits of older adults with sarcopenic obesity. The first RCT compared the effects of a hypocaloric normal protein diet (0.8 g/kg body weight/day) and a hypocaloric high protein diet (1.2 g/kg body weight/day) for 3 months in 104 older women. The results showed a significant reduction in muscle mass associated with fat mass loss in the normal protein intake group, but increased muscle mass in the high protein group. This study provided preliminary evidence that a hypocaloric diet moderately rich in proteins was able to preserve muscle mass in their participants. Another pilot RCT found a significant reduction in muscle mass in a hypocaloric diet plus placebo group compared with a hypocaloric high-protein group (1.2-1.4 g / kg body weight / day) during a 4-month diet control regimen involving 18 women. The preliminary results showed that muscle strength improved significantly in the high-protein intake group, while no observable differences in fat free mass were observed in both groups. Some limitations were observed in these two studies, including the use of loose screening criteria for sarcopenic obesity without referring to a commonly accepted diagnostic standard, little information on the participants' compliance with the dietary regimen, and an unclear randomization process and intervention components. Further studies are required to examine the effects of using a diet modification approach on sarcopenic obesity in a rigorous manner.