(P16-034-23) The Level of Methionine Deficiency Determines Its Effects on Energy Metabolism in Growing Rats

Objectives: Methionine deficiency has been reported as beneficial for health through an increase in energy expenditure and an improvement of insulin sensitivity, which in turn lowers blood lipids and adiposity, despite an increased energy intake. However, when fed to young animals, methionine-deficient diets are not suitable for growth. In the majority of studies, the consequences of methionine restriction have been studied on the same level (20% of the requirement). Thus, the aim of this study is to characterize the effects of methionine deficient levels on growth, body composition, and energy metabolism in growing rats.

Methods: Growing rats (Wistar han, Male, 50-55g) were fed for 3 weeks a control diet (P20; 20% of proteins; 100% of methionine requirement) or diets deficient in methionine at different levels: slightly (M75, 75% of methionine requirement), moderately (M60, M40; 60, 40%), and severely (M25, M15; 25, 15%). Body weight and food intake (FI) were daily measured, energy expenditure (EE) was measured by indirect calorimetry, and body composition was determined by the weighting of the main tissues and organs. Body weight was analyzed by repeated measures mixt model and other variables by one-way ANOVA.

Results: Growing rats fed methionine-deficient diets increased their FI, unless the latter is too severe (15%), probably to compensate the methionine deficiency. However, the compensation was only partial and was not sufficient to prevent the decrease in weight gain, mainly reflected by a reduced lean body mass for severely to moderately deficient diets (15, 25, 40%). In the absence of dietary compensation (15%), fat mass was also decreased. The increase in FI was maximal for the 60% diet. Rats subjected to a moderate deficiency (40 and 60%) increased their resting EE. However, this does not seem to be sufficient to expend the excess energy consumed by the 60% rats, which have an increase in body fat.

Conclusions: This study shows that the level of methionine deficiency is crucial to understand its effects in young rats. For a severe deficiency, FI can not compensate methionine deficiency and growth retardation, whereas for a moderate level of methionine deficiency, the FI increased and EE can not compensate the excess of energy intake.

Funding Sources: Institut national de recherche pour l'agriculture, l'alimentation et l'environnement (INRAE)