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

OBJECTIVES: To clarify whether the muscle fibre composition and/or muscle oxidative enzyme activity are related to dietary body weight gain and abdominal fat accumulation. METHODS: 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. RESULTS: 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). β-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. CONCLUSION: 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.