Fast/Glycolytic Muscle Fiber Growth Reduces Fat Mass and Improves Metabolic Parameters in Obese Mice
In contrast to the well-established role of oxidative muscle fibers in regulating whole-body metabolism, little is known about the function of fast/glycolytic muscle fibers in these processes. Here, we generated a skeletal muscle-specific, conditional transgenic mouse expressing a constitutively active form of Akt1. Transgene activation led to muscle hypertrophy due to the growth of type IIb muscle fibers, which was accompanied by an increase in strength. Akt1 transgene induction in diet-induced obese mice led to reductions in body weight and fat mass, resolution of hepatic steatosis, and improved metabolic parameters. Akt1-mediated skeletal muscle growth opposed the effects of a high-fat/high-sucrose diet on transcript expression patterns in the liver and increased hepatic fatty acid oxidation and ketone body production. Our findings indicate that an increase in fast/glycolytic muscle mass can result in the regression of obesity and metabolic improvement through its ability to alter fatty acid oxidation in remote tissues.
The associated press release explains things further:
Researchers used a genetic trick in obese mice that caused the mice’s muscles to bulk up as though they had been lifting weights. The researchers found that the “genetically reprogrammed” mice lost fat and showed other signs of metabolic improvement throughout the body. What’s more, those benefits were seen even though the mice continued eating a diet high in both fat and sugar and didn’t increase their physical activity at all.
Walsh’s group developed mice in which they could turn type II muscle growth on or off by flipping a genetic switch specifically in skeletal muscle. The gene they manipulated, known as Akt1, is preferentially activated in skeletal muscle in response to resistance training, but not endurance training, the researchers knew.
Rather than becoming strong and fat “sumo mice” as some of the researchers had expected, the modified mice gained type II muscle and strength while they lost fat. The mice also showed a resolution of hepatic steatosis, otherwise known as fatty liver, and improvements in a variety of other metabolic parameters. The Akt1-driven growth of skeletal muscle counteracted the usual effects of a high-fat, high-sucrose diet on patterns of gene activity in the liver and increased the breakdown of fatty acids there, the researchers showed.
This is an interesting one and shows that there is more to health than diet. There is an impact from exercise too and specifically from resistance training.
This is a call to us all to do more training to focus on the fast / glycotic muscle fibres....
You can read more about the research at:
Weight training melts fat and improves metabolism, says study of obese mice
'Weight training' muscles reduce fat, improve metabolism in mice