From: Andrew Gach <UncleWolf@worldnet.att.net>

Subject: Re: Calorie intake: BMR, RDAs and skeletal muscle fiber type

> From: "ANNIE GAZDAG" <GAZDAG@GANDALF.PHYSED.WISC.EDU>

> Subject: Re: Calorie intake

>

> Organization: U.W. Dept. of Kinesiology

>

>...I know of studies looking at this phenomenon in rats. The term used

> to describe the different populations of rats according to their

> response to diet is "resisters" and "gainers". Given a high fat

> diet, some will gain more weight than others. A colleague is studying

> whether this phenomenon is emparted by differences in fuels burned by

> asking the following: if a rat burns more fat, are they less

> susceptible to gaining weight on a high fat diet? One of the things

> believed to contribute to this differential fuel utilization is

> skeletal muscle fiber type. Studies have observed that obese

> individuals have a higher type II (fast twitch, glycolytic) fiber

> content (type I is highly oxidative and burns fat more readily). Of

> course these are not prospective studies, so we do not know if fiber

> type is affected by obesity. In other words, does the act of

> carrying more weight result in a shift in fiber type to one that is

> more suited for lifting heavy weight? Endurance (long distance)

> athletes have a higher proportion of type I fibers than sprinters,

> who have a high proportion of type II fibers.

>

Thanks for the informative survey. If nothing more, it gives some

pointers to the phenomenon described.

I wish there'd been more clinical research and on a larger scale. There

are considerable variations in human populations depending on age,

gender, lifestyle, body type, climate, genetic factors and possibly

other yet unexplored differences.

In view of the considerable variation within our own species, I don't

see the relevance of data derived from rat experiments. To extrapolate

such data to humans is no more than a leap of faith. Metabolic processes

profoundly differ from one species to another, specially in the case of

such unrelated mammals as human primates and rodents.

Perhaps the effort spent on nutritional studies conducted on animal

models would be better utilized for extending clinical research - at

least, if we wish to learn more about humans instead of rats.

Andrew Gach