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.

The inconsistent effects of nutritional interventions may have been partly caused by a short intervention duration and/or poor adherence. A clinical trial found that muscle mass remained unchanged in the protein intake group until the nutritional programme had been implemented for 24 weeks. Hence, a longer duration (at least six months) is needed for a nutritional intervention to improve muscle mass-related parameters. Poor adherence and a high dropout rate were often reported in previous similar studies. A successful diet modification intervention requires improving the participants' adherence to the diet regimen. Therefore, behavioural change techniques grounded on a tested as effective theoretical model should be incorporated within a diet modification intervention.

Rationale for developing a dietary behavioural change programme grounded on the HAPA model: The Health Action Process Approach (HAPA) model divides the process of behavioural change into two phases: motivation and volition. The motivation phase refers to the goal initiation phase. 'Self-efficacy', 'outcome expectancies', and 'increased risk awareness' are the three attributes that motivate individuals to form an intention/goal to change their unhealthy lifestyle for a healthy lifestyle. The volition phase refers to the process of implementing intentions into actual behaviour through careful planning and action execution. The empirical evidence shows that the HAPA model can be effectively used as a conceptual framework to design concrete strategies to motivate behavioural changes. Used alongside dietary interventions, these strategies can promote adherence to diet advice on increasing fruit and vegetable consumption and to healthy dietary patterns and better nutritional behaviours.

Work done by the research team: Our team conducted a systematic review of 12 RCTs with 863 participants to identify evidence-based interventions for managing the problem. The results show that exercise, especially a combination of resistance and aerobic exercises, have better outcomes than nutritional inventions. This conclusion is similar to the findings in previous systematic reviews. Our meta-analysis showed that exercise combined with nutritional interventions significantly increased skeletal muscle mass when compared with the control group that received no intervention. With all the evidence, investigators believe nutritional interventions based on dietary modifications should be used for managing the problem. Investigators conducted a pilot two-armed RCT (Clinical Trial gov. NCT 04690985) on 60 older people with sarcopenic obesity to evaluate the feasibility and preliminary effects of an Individualized Dietary Behavioural Change (IDBC) programme. The design of the IDBC programme was grounded on a tested as effective HAPA model. The feasibility of the intervention was established by an acceptable recruitment rate (57.14%), a high retention rate (83.33%), and a high attendance rate (73.33% of participants attended five out of six dietary face-to-face consultation sessions). The participants did not report any adverse events. When compared with the control group, who received only health talks, participants in the IDBC group significantly reduced their body weight (IDBC vs Control=75.28kg to 74.78kg vs 72.29±1.40kg to 73.71±1.62kg, Wald χ2=4.90, p=0.027, d=1.22) and improved the quality of their diet (IDBC vs Control=60.03±2.02 to 65.92±2.35 vs 56.83±2.11 to 57.83±2.43, Wald χ2=12.66, p\<0.001, d=1.31). Because it was a feasibility trial with insufficient power to identify significant changes, no significance difference could be identified in other outcome measurements. However, a trend of increased physical function (i.e., handgrip strength increased from \[T1\]:15.37±1.08 kg to \[T2\]:18.21±1.68 kg) and 6-m gait speed (increased from \[T1\]:0.91±0.02 m/s to \[T2\]:0.99±0.03 m/s) was observed only in the IDBC group. The use of behavioural change techniques enhanced the participants' adherence to the dietary regimen as evidenced by 66.67% of the participants adhering to the hypocaloric diet and the recommended daily protein intake, as measured by the protein score of the Dietary Quality Index (DQI). In summary, the findings from our pilot study showed that the IDBC programme is feasible. Preliminary positive effects showed that the dietary habits of older adults could be modified, leading to reduce sarcopenic obesity. In view of inconsistent results, it is also worth evaluating if any additional benefits can be observed with a combined IDBC programme with exercise in a well-design clinical trial.

The principal investigator (PI) JL and the Co-Is (CL, PK, JW) are adept at conducting intervention studies to manage frailty-related problems in older people or their caregivers. Another Co-I (SN), who is a physiotherapist academic, has conducted many RCTs using an activity-based lifestyle intervention for managing different problems in older adults. Our strength is in conducting intervention studies involving older adults in the community. Each of us has good connections with community partners, making subject recruitment feasible. The Co-Is have all contributed to developing and verifying the lifestyle intervention protocols used in the pilot study, and have worked closely with the PI to update and modify the protocols in the proposed study. LKH is a nutritionist academic and has already contributed to the proposed study by advising on the nutritional regimen in the protocol. He will work closely with the team to ensure the smooth implementation of the IDBC programme. PL provided the statistical expertise needed during the writing of the proposal and will employ these skills in analysing the data from the study.