Sarcopenic obesity is a lack of muscle (thin, weak muscles) in someone with obesity (a body mass index over 30 kg/m2). However, it is now also recognised in some individuals with a normal weight but with increased body fat percentage.
The main cause is ageing. However, since the onset of the obesity epidemic and the increase in sedentary lifestyles, sarcopenic obesity is becoming more common in younger individuals.
Sarcopenia limits mobility, which will affect quality of life and the possibility for independent living. It also impairs balance, increasing the risk of falls and fractures. The association of sarcopenia with obesity exacerbates these changes.
Loss of muscle intensifies the metabolic changes associated with obesity, increasing the risk of obesity-related diseases, such as diabetes, hypertension and heart disease.
Treatment is difficult, as it requires us to reduce body fat at the same time as we are trying to build new muscle. Specific exercise regimens must be combined with an individualised nutrition programme that will promote weight loss while providing all the nutrients needed to rebuild muscle. Progress is monitored using body composition analysis plus tests of muscle strength.
Please read on if you would like a more in-depth review of sarcopenic obesity.
What is sarcopenic obesity?
Sarcopenia is a loss of muscle mass associated with a poor function of the remaining muscle (see my article on sarcopenia.) In this article I shall comment on the simultaneous presence of sarcopenia and obesity.
Sarcopenic obesity is, as its name suggests, a condition in which a loss of muscle and poor muscle function coexist with obesity.
Up to now, the definition of obesity has depended on body mass index (BMI). However, we are becoming increasingly aware that it is not the overall weight but rather an excess of body fat that is the major determinant of the effects of obesity on health (see my article on body fat percentage here.) This said, BMI is a perfectly valid criterion in the large majority of patients, and a BMI over 30 kg/m2 is the most commonly used criterion in the definition of sarcopenic obesity.
The main cause of sarcopenia is ageing, due to the hormonal changes in the body together with a poor diet, gastrointestinal disorders and reduced physical activity. These same changes can also provoke obesity. Since the onset of the obesity epidemic and the increase in sedentary lifestyles, sarcopenic obesity is becoming more common in younger individuals, especially when repeated dieting using poorly designed weight-loss programmes has led to weight yoyoing.
Obesity is closely associated with a decrease in physical activity in many cases, and physical activity is the main stimulus for muscle maintenance and growth. A sedentary lifestyle can provoke a loss of muscle, but in obesity there is the added problem of ectopic fat accumulation in muscle tissue (ectopic = not in a normal location). This is called myosteatosis and is a form of abnormal fat storage. Myosteatosis interferes with normal muscle function and metabolism.
How is sarcopenic obesity diagnosed?
A diagnosis of sarcopenia requires a demonstration of decreased muscle mass associated with poor muscle strength. Muscle strength is assessed using functional tests such as hand grip strength or rising repeatedly from a chair. Evaluation of muscle loss requires specific tests, such as a DEXA scan or bioelectrical impedance analysis (see my article on bioimpedance here.) These tests give us reliable estimates of the proportions of different tissues in the body and can be used for diagnosis and monitoring.
Sarcopenic obesity is diagnosed when sarcopenia is present in an individual with a BMI over 30 kg/m2 or a high body fat percentage (men, >25%; women, >33%).
Why is it important to detect sarcopenic obesity?
Sarcopenia and obesity both independently affect health and quality of life, and each can amplify the effect of the other. A vicious circle can develop, in which reduced mobility and poor diet lead to sarcopenia and obesity, which provoke a further reduction in activity.
The typical effects include the following:
- Decreased mobility, affecting quality of life and independent living
- Impaired balance, predisposing to falls and fractures, particularly in the elderly. Hip fractures in persons over 50 years of age increase mortality risk by 5 to 8 fold.
- Insulin resistance (increased risk of type 2 diabetes)
- Other complications of obesity, such as heart disease, stroke, cancer… (see here for more details on obesity-related disease.)
Ectopic fat storage in and around muscles (see above) reduces muscle strength and interferes with glucose uptake by muscle tissue by inducing insulin resistance. Insulin resistance increases the risk of type 2 diabetes, with all its possible complications (visual deterioration, kidney disease, neuropathy, vascular disease, amputations…).
Sarcopenic obesity is therefore highly significant not only for individual health but also because it increases the burden on our already stretched health services.
The treatment of sarcopenic obesity is difficult, as it requires us to reduce fat mass at the same time as we need to build up muscle mass. Simple dietary measures of reduced energy intake are ineffective or even counterproductive.
Good adherence to a specifically designed exercise programme is essential to improve muscle mass and performance. This must be combined with an individualised diet that will promote weight loss while providing all the nutrients needed to rebuild and strengthen muscles. Sometimes weight remains stable, but this is often not a sign of failure, as muscle mass may increase at a similar rate to the decrease in fat mass. This substitution of fat by muscle, within a guided exercise and diet programme, will act to reverse the metabolic abnormalities, improving muscle function and decreasing insulin resistance.
Monitoring efficacy using bioimpedance body composition analysis plus functional tests of muscle strength and performance, will enable relevant adjustments to be made to the programme.