Andrew Millard wrote:

>But both these studies are on diets of average to low calories compared to
>recommended adult intakes.  What's the difference in weight gain between
>people on, say, 4000-calorie and 1000-calorie diets?  It's not surprising
>that at constant calories the composition of the diet can make a
>difference, but reducing calories has an effect too.  It seems incredible
>to me that adults on a 1000-calorie diet could gain weight, as their
>metabolic expenditure ought to exceed this with even a modest amount of
>activity, and if the energy is not coming from burning of body reserves,
>then our fundamental understanding of where biological systems get their
>energy from is in doubt.
>
>

The thing that has not been sufficiently studied, in my opinion, is not
simply weight loss on isocaloric diets of varying macronutrient ratios,
but changes in body composition.  That said, however, there are studies
that suggest that lower carbohydrate diets preserve lean body mass and
favor fat loss, in comparison with higher carb diets of comparable
energy content.  For example, the small study done by Charlotte Young in
the early 1970s showed exactly this effect.  All consumed 1800
kcal/day.  All consumed 115g/day of protein.  Only the fat and carb
content was varied.  Those eating the most fat (133g/day) and least carb
(30g) lost more body fat and less LBM than those getting more carb
(104g/day) and less carb (103g/day).  There was also a modest but
significant difference in total weight loss.

This was a small study.  There need to be more studies like this.  But I
think recent studies that have been done (finally) on lowcarb diets tend
to confirm Young's results (e.g., Layman's study).

 From the standpoint of the obesity problem, these findings are
tremendously important.  Weight loss that involves a significant loss of
LBM is very likely to result in rebound weight gain, due to the ensuing
drop in metabolic rate.

In support of Barry Groves' opinion that humans have differentiated
themselves from other primates by becoming largely carnivorous, I
recommend Craig Stanford's book The Hunting Apes: Meat Eating and the
Origins of Human Behavior.  Stanford's emphasis is not nutritional, but
he makes a very strong case for the claim that our species has, of
necessity, followed an adaptational trajectory of increasing carnivory.

Todd Moody
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Charlotte Young, Weight Loss on 1800 kcal Diets varying in
Carbohydrate Content. Am J of Clin Nut 1971 290-6.

Craig B. Stanford, The Hunting Apes: Meat Eating and the Origins of
Human Behavior. Princeton University Press, 2001.