Obesity and Sarcopenia: The Importance of Muscle Mass in Management

According to a recent expert consensus¹, obesity is defined as a condition characterized by a body mass index (BMI) greater than 30 kg/m², combined with excess fat mass that leads to clinical complications impairing the patient’s health. From a pathophysiological perspective, this excess fat mass causes low-grade systemic inflammation due to the production of pro-inflammatory cytokines by adipose tissue (i.e., adipokines). When associated with a diet high in simple carbohydrates and saturated fats and/or a sedentary and physically inactive lifestyle, this systemic inflammation contributes to metabolic complications (e.g., type II diabetes) and cardiovascular issues (e.g., hypertension or myocardial infarction)². Additionally, excess fat mass and body weight increase mechanical stress on the musculoskeletal system (i.e., muscles, skeleton, tendons, etc.), which stimulates higher bone mass and skeletal muscle mass. Mechanical stress is indeed the primary driver of muscle protein synthesis and bone tissue mineralization³⁴, meaning individuals with obesity typically exhibit elevated muscle and bone mass.

Despite this observation, sarcopenia has already been reported in individuals with obesity⁵⁻⁷, which may seem counterintuitive. Sarcopenia is defined as a decline in muscle mass and function caused by aging and/or chronic conditions such as cancer or heart failure⁸⁻¹⁰. Pathophysiologically, sarcopenia results from increased muscle protein breakdown¹¹, combined with sedentarism and physical inactivity. This has significant consequences for patients’ daily lives, reducing their quality of life and potentially leading to frailty¹². Specifically, reduced maximal strength in these patients increases the physiological load imposed by daily activities on the body, causing fatigue. Exercise induces physiological and psychological changes that trigger neuromuscular fatigue, defined as a reversible decrease in force production caused by exercise and alleviated by rest¹³.

In daily life, neuromuscular fatigue encompasses the sensations and experiences that lead individuals to stop or struggle with an activity. For patients with sarcopenia, reduced maximal strength increases the perceived intensity of daily activities and the fatigue they generate. As these activities repeat throughout the day, patients fail to recover from the physiological load imposed by exercise, leading to accumulated physical and psychological fatigue¹⁴. This mechanism fuels a vicious cycle that promotes sedentarism, physical inactivity, anxiety/depression, and physical deconditioning¹². Consequently, patients find it increasingly difficult to perform daily activities, which generate even greater fatigue, perpetuating the cycle.

In absolute terms, individuals with obesity do not exhibit reduced maximal strength or muscle mass; however, these values remain insufficient relative to their body weight. Their body mass is so high that they must generate extreme force to move⁵. This creates conditions where daily activities impose an excessive physiological load, promoting gradual physical deconditioning and worsening clinical health. Thus, it is critical to monitor muscle mass in patients with obesity and ensure it is sufficient to comfortably perform daily activities. Conversely, tailored interventions to reduce fat mass and/or increase muscle mass become necessary.

Several therapies can be considered: bariatric surgery, nutritional interventions, adapted physical activity, or, more recently, GLP-1 analogue treatments. Bariatric surgery and GLP-1 analogues aim to reduce fat mass by lowering caloric intake. However, despite their efficacy, these approaches can cause significant muscle loss¹⁵,¹⁶, potentially leading to sarcopenic obesity and worsening the patient’s condition. They must therefore be combined with nutrition and exercise programs designed to prevent muscle loss¹⁷. In this context, muscle mass must be monitored throughout treatment to avoid therapy-induced decline.

Lifestyle management (i.e., nutrition and physical activity) can also reduce fat mass and/or preserve muscle mass if properly tailored. Patients should engage in combined resistance and aerobic exercise to maintain or gain muscle mass while promoting fat loss and cardiovascular health. Nutritionally, this should be paired with a high protein intake to support muscle growth and fat loss (via the satiety-inducing effects of protein), alongside a balanced diet. Body composition should be regularly assessed during treatment to evaluate progress and maintain patient motivation, as these processes are long-term.

Conclusion

Skeletal muscle is a vital organ for health, and a decline in its mass over time can severely impact clinical outcomes. Sarcopenia, defined as reduced muscle mass, typically arises with aging or chronic diseases but may also occur in obesity, where muscle mass becomes insufficient relative to body weight. Surgical, therapeutic, and/or lifestyle interventions can mitigate this by reducing fat mass and/or increasing muscle mass. Monitoring body composition throughout management is essential.

References

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