The mainstream solution to weight gain is a forced calories restriction diet and aerobic exercise. These are often used in combination in order to elicit a ‘negative energy balance’ which is assumed will cause weight loss. Often weight loss does result from such a strategy, but what is often not explained is that this weight loss includes a large amount of skeletal muscle mass and internal organ weight. For example in one study researcher investigated the effects of a dietary lifestyle interventions on overweight subjects with type 2 diabetes. One of the interventions was successful at causing weight loss in the subjects which amounted to a significant 6.6 kg over the course of one year. However, by year two some of this weight had been gained back and so at the year 2 point, weight loss amounted to 5.2 kg. Around 1.4 kg of the lost weight was skeletal muscle, and this was from both appendicular and trunk muscle mass. The subjects regained their appendicular skeletal muscle mass in the second year, but their trunk mass did not return.
Compared to many studies the skeletal muscle loss in this group of subjects was not extreme, but it does illustrate that skeletal muscle mass will be lost when energy restriction occurs. This study also noted that there was a significant reduction in the weight of some of the internal organs, most notably the liver and the spleen. Some of this weight could have been associated fatty tissue, as the liver particularly will increase its weight due to fatty acid accumulation. There was also a significant decrease in the mass of the kidneys of the subjects. Weight loss using forced energy restriction and aerobic exercise to cause a negative energy balance does therefore have a downside, and care should always be taken in such matters. That trunk skeletal muscle mass did not return may be due to the lower body weights that required less support, or may have been for other reasons. If this was for other reasons, this is concerning, and highlights that some weight loss changes are semi-permanent in nature, and could have long term health implications.
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