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The battle of the bulge: defense versus offense

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Alex’s Notes: The article at hand is a short editorial by Magkos and colleagues whose title caught my eye. After reading through it, I thought it was worth sharing. We all know that obesity is – fundamentally – caused by consuming more energy than expended, and that weight loss is the result of creating a negative energy balance. Yes, there are numerous factors that can influences intake and expenditure, but the bottom line is the same. During times of caloric restriction and dieting, weight loss results in a decrease in energy expenditure for the simple reason that there is less body mass that needs energy. Even in the Minnesota Starvation Experiment 25% out of the 40% decrease in metabolic rate was due to lower body mass. Thus, when eating an amount that enables a certain rate of weight loss, an eventual plateau will be reached in which the intake is once again in balance with expenditure.

This raises the question of why weight loss is so hard to maintain, and one of the most prominent theories to answer said question is that a complex neuroendocrine system regulates food intake and energy expenditure to defend a certain “set-point” in body weight. In fact, one recent study sought to expand the details of this theory by analyzing weight loss in normal-weight, overweight, and obese persons who lost weight via dieting and via gastric bypass surgery. The authors suggest that, despite the differences in magnitude of weight loss and the mechanisms responsible for weight loss among diet and different surgical therapies, the reduced body weight is still governed by a predetermined set point, and they propose a ‘‘threshold shift paradigm’’ for the relation between adiposity signals (particularly leptin) and body weight control.

However, as Magkos points out,

“A simpler mechanism than the ‘‘threshold theory’’ could explain this relation. In general, daily energy expenditure is directly correlated with BMI, and ‘‘large’’ people require greater energy intake to maintain body mass than do ‘‘small’’ people. Accordingly, the negative energy balance induced by a specific reduced energy intake is greater for large than for small people. It is possible that the range of actual (not prescribed) energy intake (or absorption) of obese people prescribed a hypocaloric diet or who have had bariatric surgery is limited, so that the relatively larger persons will invariably be at a greater negative energy balance and will therefore lose more weight than the relatively smaller persons.”

No doubt, the authors of the study in question found an elegant explanation for their data, but seem to ignore that body weight is the result of a complex interaction between not just energy intake and expenditure, but also genetics, behavioral, developmental, lifestyle, and occupational factors. Even food availability and marketing will play a role.

The above isn’t disregarding the set-point theory. Rather, it emphasizes that additional research is needed to understand the importance of this adaptive biological response within the context of the myriad of other underlying inherent and acquired factors that led to excessive energy intake and body fat in the first place.

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