Muscle mass and health: relation with nutrition, physical activity and comorbidities in different weight classes

Overweight and obesity are a growing societal problem, affecting respectively 1.9 billion and 650 million people worldwide. In the Netherlands, the number of people with overweight and obesity is rising as well, with more than half of the population being overweight and approximately 15 percent of them having obesity.1,2

In obesity, the focus is mostly on fat mass and the reduction of this mass, because fat mass is an important determinant of co-morbidities e.g. type 2 diabetes and hypertension. The muscle mass is usually not taken into account. The health risks of low muscle mass have been documented in populations of older adults, however awareness of low muscle mass and its health risk in obesity are lagging behind.3,4 It is known that in obesity low muscle mass and function are associated with a worse outcome, e.g. lower psychological health, lower quality of life and increased all-cause mortality.5,6 Furthermore, lower muscle mass and strength are predictors for type 2 diabetes in older adults.7 However, similar studies about the correlation between muscle mass, strength and comorbidities have yet to be performed in populations with obesity.

Weight reduction by regular diets is associated with some reduction in muscle mass. However, in the more extreme weight loss therapies, e.g. very low calorie diet, most of the weight loss was surprisingly due to the loss in muscle mass and not fat mass (loss of lean body mass: 2.8 kg, loss of fat mass: 1.6 kg).8 In the first months after bariatric surgery, there is also more muscle mass lost relative to fat mass(loss of lean tissue mass: 9.7 kg, loss of fat mass: 7.7 kg).9 One of the main causes of this muscle mass loss seems to be the lack of proteins in nutrition. Furthermore, in the case of bariatric surgery, in the first month after surgery, the physical activity will also be lower which can also play a role in the high amount of muscle mass loss. Nutrition seems to play an important part in retaining muscle mass while losing weight. Protein seems to be a key factor in retaining (and possibly even increasing) muscle mass. Next to nutrition, another important factor in retaining muscle mass is the physical activity. For clinicians treating obesity and overweight, either by diet, medication or bariatric surgery, information on muscle mass and factors involved in preservation of muscle mass is of great importance.