Mice long-term selected for high body mass are more susceptible to body fat deposition in response to a high fat diet due to insufficient increase in heat production

Abstract. Using a mouse model long-term selected for high body mass (DU6i), we investigated if their higher degree of body fat as compared to unselected controls (DUKsi) was due to a greater fat accumulation, attributable to differences in substrate oxidation in response to a higher fat intake.

We measured energy expenditure (EE) and substrate oxidation by indirect calorimetry at the ages of 42 d and 98 d in response to a fat rich diet compared to a standard diet (F, 20 %; C, 5 % fat) introduced at weaning (21 d). The EE to food energy intake ratio (Q) was calculated and uncoupling protein (UCP1) mRNA expression was analysed in brown adipose tissue in male mice of both strains. The F diet increased body and fat mass in DU6i (P<0.05) but not in DUKsi. Energy intake was not influenced by diet in both strains, but EE was lower in DU6i than in controls (P<0.05). In contrast to DU6i, fat oxidation was higher in DUKsi mice fed the F diet until the age of 42 d (P<0.05). At the age of 42 d, the Q value was lower in DU6i, and higher with F diet irrespective of strain. UCP1 mRNA expression was twice as high in DUKsi as in DU6i (P<0.05).

Between 42 d and 98 d of age, DU6i mice were more susceptible to body mass gain and fat deposition in response to the F diet due to insufficient increase in fat oxidation and energy expenditure possibly related to lower UCP1 mRNA expression.