Will Dieting Make You Fatter? Only If You Are Skinny!

Professor Abdul Dulloo, University of Fribourg, Switzerland

Professor Abdul Dulloo, University of Fribourg, Switzerland

At the recent European Congress on Obesity, I had the occasion for a long chat with my friend and colleague Abdul Dulloo, from Friburg in Switzerland, who has worked extensively on the issue of weight regain.

I asked him how much evidence there is to support the common notion that losing weight makes you fatter – something many dieters claim to have experienced.

Indeed, both in animals and humans, weight loss, as a rule, is followed by a more rapid regain of body fat than lean body mass (i.e. preferential catch-up fat) than of lean body mass, as a result of which body composition post-weight regain results in a greater proportion of fat mass than before. But does this increased “fatness” persist over time?

This is where Dulloo made me aware of a recent paper he published in Obesity Reviews that examines this question.

What his analysis of prospective studies on this issue revealed is that paradoxically, people within a the normal weight range appear much more prone to weight gain over time with dieting than people who already have overweight or obesity.

Indeed as he points out,

“…it is dieting to lose weight in people who are in the healthy normal range of body weight, rather than in those who are overweight or obese, that most strongly and consistently predict future weight gain.”

The reasons for this rather unexpected finding are unclear and some have argued that repeated dieting to lose weight in normalweight people may represents unsuccessful attempts to counter genetic and familial predispositions to obesity – these people are genetically prone to weight gain, which is why they are dieting in the first place. Thus, rather than a causal relationship, the association between dieting and subsequent weight gain is just what would have happened to them anyway.

Others have argued that the metabolic effects resulting from the psychological “fear of fatness” (which prompts dieting) per se may increase the risk for weight gain hence a contributing factor to the obesity epidemic.

However, as Dulloo and colleagues discuss at length, based on their reanalysis of a wide range of human studies of weight loss and refeeding on body composition data on fat mass and fat-free mass (FFM) losses and regains, there is increasing support for the biological plausibility that dieting predisposes lean individuals (rather than those with overweight or obesity) to regaining more body fat than what had been lost (i.e. fat overshooting).

Overall the findings suggest that perhaps the reason why lean people regain fat faster is because their feedback signals in response to the depletion of both fat mass (i.e. adipostats) and fat-free mass (i.e. proteinstats), through the modulation of energy intake and adaptive thermogenesis, are more effective than in individuals with overweight or obesity, thus resulting in a faster rate of fat recovery relative to recovery of lean tissue (i.e. preferential catch-up fat).

In fact, it appears that lean people overshoot in terms of weight gain because the state of hyperphagia (in response to weight loss) appears to persist well beyond complete recovery of fat mass and interestingly until fat free mass is fully recovered (which may take months during which time fat gain continues).

Thus, it appears that in lean individuals “fat overshooting” following a diet is a prerequisite to allow complete recovery of fat-free mass (in obese individuals this may be less of an issue as recovery of fat-free mass is stimulated simply by the need to carry around a greater body weight).

Thus, it is easy to understand why repeated dieting and weight cycling would increase the risks for trajectories from leanness to fatness particularly in people who have a normal weight to begin with.

These findings have important public health implications and for promoting a “fear of fat”.

As Dulloo notes,

“Given the increasing prevalence of dieting in normal-weight female and male among young adults, adolescents and even children who perceive themselves as too fat (due to media, family and societal pressures), together with the high prevalence of dieting for optimizing performance among athletes in weight-sensitive sports, the notion that dieting and weight cycling may be predisposing a substantial proportion of the population to weight gain and obesity deserves greater scientific scrutiny.”

Indeed, I wonder how much of the obesity epidemic is directly attributable to normal weight people trying to lose weight for no good reason other than to look better.

Edmonton, AB

ResearchBlogging.orgDulloo AG, Jacquet J, Montani JP, & Schutz Y (2015). How dieting makes the lean fatter: from a perspective of body composition autoregulation through adipostats and proteinstats awaiting discovery. Obesity reviews : an official journal of the International Association for the Study of Obesity, 16 Suppl 1, 25-35 PMID: 25614201