Poster Presentation Australian & New Zealand Obesity Society 2015 Annual Scientific Meeting

Exercise counteracts the inhibitory effect of dieting on thermogenesis. (#230)

John-Paul Fuller-Jackson 1 , Iain J Clarke 1 , Belinda A Henry 1
  1. Metabolic Disease and Obesity Program, Biomedicine Discovery Institute, Department of Physiology, Monash University, Clayton, Victoria, Australia

Thermogenesis is a form of energy expenditure where cellular energy is dissipated as heat, a process which occurs in response to cold or feeding in brown adipose tissue (BAT) and skeletal muscle. Food restriction causes a homeostatic reduction in thermogenesis, in effort to prevent weight loss, whereas exercise may increase thermogenesis. We aimed to determine whether exercise counteracts the decrease in thermogenesis caused by dieting. Ewes were assigned to 4 groups (n=5); 1) sedentary, ad lib diet, 2) exercise, ad lib diet, 3) sedentary, diet (30% food restriction) and 4) exercise, diet. Exercise involved running at 8km/ h for 30 minutes/ day, 5 days/ week, for 4 weeks. Tissue heat production was continuously recorded in sternal fat, retroperitoneal fat and skeletal muscle. Body fat content was reduced (P<0.05) in the diet/exercise group only (ad lib, sedentary animals gained 1.48±0.48 kg whereas diet/exercise group lost 0.26±0.21 kg). Diet alone reduced the gain in lean mass (P<0.05, ad lib, exercise animals gained 4.646±0.85 kg while diet, sedentary animals gained 0.2940±0.82 and diet/exercise 1.45±1.046 kg). Food restriction reduced (P<0.05) night time thermogenesis in sternal and retroperitoneal fat (Sternal fat ad lib: 38±0.2 ⁰C vs diet: 36.7±0.7 ⁰C; Retroperitoneal fat ad lib: 39.5±0.1 ⁰C vs diet: 39.0±0.2 ⁰C). There was no effect of exercise on thermogenesis in ad lib fed animals. The diet-induced reduction in thermogenesis, however, was partially reversed by exercise in sternal fat (37.3±0.1 ⁰C). Skeletal muscle heat production was not affected by diet or exercise. We conclude that dieting induced a homeostatic reduction in thermogenesis, primarily in adipose tissue depots and this occurs predominantly at night. Notably, exercise is able to counteract the inhibitory effect of food restriction on thermogenesis.