Obesity‐prone high‐fat fed rats reduce caloric intake and adiposity and gain more fat‐free mass when allowed to separate protein from carbohydrate/fat intake

Abstract

Dietary fat is among the factors often considered responsible for the high prevalence of adiposity. Both genetic and epigenetic factors influence who in a population will develop adiposity and it is established that humans as well as rodent models are not uniformly sensitive to adiposity gain under high fat diets.In addition it is also recognized that when placed on dietary self‐selection (DSS) conditions, most species are generally able to select an adequate diet for growth and maintenance. In most cases, caloric intake and body weight gain suggest that DSS is closely related to nutritional and physiological requirements. In one previous studies (1), when shifted from a control (low‐fat) mixed diets to DSS rats spontaneously increased protein and strongly decreased caloric intake (−40%) together with preservation of a normal growth which suggested that before DSS rats ate more food in order to increase protein intake.The present study tested the hypothesis that in rats fed a high fat diet (HFD), and particularly in individuals prone to adiposity gain (“fat sensitive”, FS, as opposed to “resistant”, FR), a prioritisation of maintaining protein intake could be involved in the excess energy consumption and hence obesity when fed diet with a protein content considered as too low by the animal. For that purpose, male Wistar rats first received three weeks of HFD (by energy ‐ Protein 15%, Fat 42%, Carbohydrate 42%) under which they were characterised as being FS or FR and then were switched to the same HF diet but in which protein was available separately from the carbohydrate/fat mixture (DSS).The results showed that under this DSS regimen, FR as well as FS rats maintained a similar intake of protein whereas intakes of fat and carbohydrate were reduced by 50%. Overall intake was: protein 27%, carbohydrate 37%, and fat 37%, ie caloric intake remained high in fat. All rats separated in time the ingestion of protein and that of the carbohydrate/fat mix, i.e. avoided to mix again the 3 macronutrients. In both FR and FS rats, adiposity gain was prevented and, in FS rats only, fat free mass gain was increased. Analysis of mRNA showed that enzymes expression of genes coding for lipogenesis was larger in liver and adipose tissue of FS rats.These results show that high‐fat fed rats were able to strongly reduce food intake and adiposity gain through macronutrient selection and that this response occurred in FS rats despite maintenance of mechanisms favoring fat storage.