Section: New Results

Variable food availability increases weight: a mathematical prediction

Participant: H. Soula

Due to the conservation of energy, the energy storage in adipose tissue reflect the difference of energy expenditure and energy intake. Without change in physical activity, the main paradigm has always been that this storage does not depend on the timing of intake but on its whole temporal integration: the overall food intake. However, mammal and especially rats can compensate energy expenditure to save energy in case of starving. This adaptation should provoke variation in energy expenditure when food availability varies in time. Using animal experiments and mathematical modelling, we showed that indeed food availability variation - while conserving the same amount of energy - can disrupt and perturb energy balance. Submitted to variation in availability with a period above 4 weeks, rats where bigger with higher fat mass than control. Even so these rats had eaten the same amount of food as the control group during the same period. Our mathematical model uses delay equations and can predict both the food intake and the body weight variations. We showed that delay in energy saving adaptation cause this variation and estimate the lag at 1 week. This result could very well apply to humans in the so called 'yoyo regime'. Regime that are stopped are a typical case of food intake variation and could cause greater fat accretion instead of body weight reduction. We show that this should happen if the regime lasts longer than one week.

This result has been the subject of an article in the weekly journal of Inserm Rhônes-Alpes with an interview of author H. Soula.