Metabolic damage. It’s every dieter’s worst nightmare. The theory of metabolic damage states that your metabolism slows down permanently, i.e. is damaged, after prolonged periods of being in energy deficit. This decrease in energy expenditure has been used to explain the occurrence of the yo-yo effect whereby people that have dieted for a long time often quickly regain their lost fat when they stop dieting.
But so far no scientific publication has actually scrutinized the theory of metabolic damage, so the Bayesian research team sought to investigate whether metabolic damage actually occurred. Our findings have now been published in the Medical Research Archives.
For a less technical and more lay friendly explanation, see Menno’s opening statement in the reverse dieting debate with Layne Norton, Eric Helms and Peter Fitschen.
Human metabolism is strongly affected by an individual’s body composition, with lean body mass, in particular organ mass, having a strong positive relation with energy expenditure and fat mass having little direct effect on energy expenditure. However, fat mass stores do relate with adaptive thermogenesis, the phenomenon that your metabolism, particularly your non-exercise physical activity level, decreases along with body fat stores.
Secondly, human metabolism is significantly affected by energy intake with higher energy intakes resulting in higher energy expenditure.
When you take body composition and energy intake into account, there is no evidence of metabolic damage in the literature. This includes anorectic women, malnourished individuals, research for the Second World War on the effects of starvation, bodybuilders during contest prep and wrestlers that aggressively make weight for their competitions. Human metabolism adapts, but even in extreme cases it does not suffer permanent damage. As such, metabolic damage can be considered a myth.