Dietary obesity-resistance and muscle oxidative enzyme activities of the fast-twitch fibre dominant rat.

Abstract

To clarify whether the muscle fibre composition and/or muscle oxidative enzyme activity are related to dietary body weight gain and abdominal fat accumulation. Genetically fast-twitch fibre dominant rats (FFDR) and control rats (CR) were divided into low-fat (20% of energy from fat) or high-fat (60% of energy from fat) diet groups: CR with a low-fat diet (CL); CR with a high-fat diet (CH); FFDR with a low-fat diet (FL); and FFDR with a high-fat diet (FH). After 6 weeks of following such diets, the body weight gain, abdominal fat content, food intake, muscle fibre composition and oxidative enzyme activities were estimated. The total body weight gain in CH was from 18 to 62% higher than in the other groups (P<0.05) and percentage abdominal fat in CH was also from 26 to 61% higher than in the other groups (P<0.05), while the energy intake did not differ among the groups. The percentage of type IIX fibres of M. gastrocnemius in FL (33.4%) and FH (36.3%) were higher than in CL (16.8%) and CH (19.8%; P<0.05), and the type IIA fibres of M. soleus in FL (14.1%) and FH (11.8%) were higher than in CL (2.0%) and CH (3.5%; P<0.05). The citrate synthase (CS) activity of of M. plantaris in FL and FH were higher than CL (46 and 54%, respectively, P<0.05). beta-Hydroxyacyl CoA dehydrogenase (HAD) activity in FL and FH were higher than in CL (21 and 31%, respectively, P<0.05) and that in FH was higher than CH (23%, P<0.05). On the other hand, the enzyme activities of M. gastrocnemius and soleus were identical among the groups. The FFDR was more obesity-resistant than the CR after a high-fat diet. These results suggest that the muscle oxidative capacity rather than muscle fibre composition is a possible determinant of obesity.