From: "ANNIE GAZDAG" <GAZDAG@GANDALF.PHYSED.WISC.EDU>
Subject: Re: Calorie intake
Organization: U.W. Dept. of Kinesiology
Priority: normal
> Date: Tue, 25 Feb 1997 10:19:53 +0100
> From: hgl@sgmf02.med-forschung.uni-marburg.de (H.G.Loeffler)
>
> Being not a nutritionist, I wonder whether somebody can help me in sorting
> out an intriguing observation.
>
> How is it possible that persons with a similar caloric intake gain
> differently in weight? Can this difference simply be linked to a variable
> basic metabolic rate?
Some studies indicate that lower basal metabolic rate is predictive
of future weight gain. I cannot off the top of my head cite these
studies, but most come out of American universities in the desert
southwest (Arizona, Utah, New Mexico) who use Pima Indians as their
population of interest. I do not know the broader literature on this
subject well enough to critically assess the importance of a 50kcal
per day difference in metabolic rate. Practically speaking however,
daily kcal intake can vary tremendously, much more than by 50kcals a
day, and most of us maintain stable weights (within a kg) despite
this variation. Some have thus speculated that certain
individuals lack the ability to regulate energy balance and thus
accumulate very effectively all excess calories ingested.
Normally, if one overeats on one day, their metabolic rate
increases, just as it decreases when too few calories are
ingested on another day. Also, a few flights of stairs or walking
around the block can take care of 50kcals, so if this 50kcal/day BMR
deficit is REALLY a major contributor to obesity in the Pima
population, I have a simple approach to solving that problem.
Interindividual variation in BMR is not the only factor believed to
contribute to interindividual differences in body composition and
mass. Claud Bouchard at U Lavale has done some interesting
overfeeding studies in identical twin pairs and found that with a
similar increase in daily kcal intake, the amount of weight gained
and the composition of the body mass gained varied greatly between
pairs, and was very similar within pairs (ie, brothers were more
similar).
> I don't think that such a mechanism can account for the observed
> great individual differences. I recently heard that the number of
> calories derived e.g. from fat might vary within persons.
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 readliy). 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 portion of type II fibers.
> If this is true, the practical value of food tables would very
> limited. Is there a way of finding out whether I can trust these
> values or do I have to assume that I belong myself to a group of
> persons which utilizes fuel in a different manner?
>
> H.G. Loeffler
How is it that you are assessing whether you are in equal caloric
balance relative to whomever it is you are comparing yourself to?
Body composition will greatly affect BMR, and also other
components that make up total caloric expenditure. Given
similar weight, the more lean body mass you have the more calories
you will expend doing a given activity, like an evening 5mile run.
Although caloric balance is essential for weight maintenance, you are
correct in questioning whether a food calorie of fat and a food
calorie of carbohydrate truly equal the same caloric value in
the body. We know that the body must expend more energy to store a
given amount of protein and carbohydrate as fat than if the same
excess fat calories are stored as fat. I recall some rat studies
that showed on equicaloric diets, rats fed high fat diets had more
body fat and less lean mass than rats fed a high carbohydrate diet.
So, just because you eat the same calories as another individual of
similar size, the composition of your diet may impact whether you
gain fat and this other person does not.
With respect to the practical value of food tables, they are limited
to begin with. The RDAs suffer from the same deficiency. I am 5'1".
How can I possibly have the nutrient requirement as a woman who is 6'
tall? If you exercise a lot or have much more lean mass than someone
of similar stature, how do your nutrient requirements change? We
don't know. Food tables cannot possibly account for interindividual
differences in GI motility, fuel utilization, body composition and
other genetic influences. The numbers in these tables can be
"trusted" in that a cup of rye flour and a cup of wheat flour
were both burned in a bomb calorimeter, analyzed for nitrogen content
and fat content in the same way. Just because your body doesn't use
food in the same way as someone else's doesn't invalidate the
information in food tables. They are a reference, not the absolute
truth for you as an individual.