Fiber type seems to be related to obesity:
In a study, obese women Resting Metabolic Rates fell within 2% of that of lean women.
However, fat oxidation was considerably higher in lean women than in their obese counterparts - at least during exercise at 65% VO2 max.
We all know slow twitch muscle fibers are oxidative and fast twitch - particularly type IIb are glycolitic. It would stand to reason obese women would have less type I fibers and disporportionate ammounts of type IIb fibers.
There are SEVERAL studies supporting this. I one, white lean women had an average of 14.4% type IIb fibers and 54.6% type I fibers. Their obese counterparts has 25.1% type IIb fibers and only 41.5% type I fibers.
Additionally several studies support the notion that type IIb fibers are insullin resistant whereas type I fibers are insulin sensitive in comparison. I should point out though another study reported the biger factor in insulin sensitivity would be cappilary density and not fiber type. That is to say, the more cappilaries you have in a muscle the more insulin sensitive itll be. Thus type I are more insulin sensitive than type IIa which beat type IIb.
One study pointed out rats which were put in a hyperinsulinemic state saw an increase in the proportion of their type IIb fibers. They also saw a prefered nutrient partitioning effect in which glucose was preferably taken to type IIb fibers.
I have all the references down if you’re interested. If I wasnt pressed for time I’d make this a much better post, but I thought it was pretty interesting.