From: bradbury@sftwks.UUCP (Robert Bradbury)
Newsgroups: sci.med.nutrition
Subject: Re: Tradeoffs between reproduction and repair [was: weight gain]
Summary: Malnutrition and caloric restriction have different effects
Keywords: reproduction, weight gain, DNA repair
Date: 8 Sep 92 18:41:09 GMT
Organization: Softworks Ltd, Seattle, WA

My previous comments were about the evolutionary advantage of shifting
resources from reproduction to maintenance and repair when calories
are restricted.

In article <1992Sep8.070445.6093@u.washington.edu>
  y8321@carson.u.washington.edu (Yih-Jin Young) writes:
> 
>According to John Bongaarts, malnutrition can impair the function of the 
>human reproductive process.  This effect is strongest and most evident in
>famine and starvation, when both fecundity and fertility are reduced 
>significantly.  Moderate chronic malnutrition has only a minor effect on 
>fecundity.  He further suggests that a large improvement in the nutrition
>of the mothers in the underdeveloped countries will at most result in a 
>slight increase in fertility. Other studies (Menken, Trussell, and Watkins)
>also show a weak link between nutrition and fertility.  
>Based on the studies listed above,  your proposed relationship may not be
>very convincing.
> 
It is *VERY* important to differentiate between malnutrition and caloric
restriction.  Famine and starvation are conditions in which there may
be shortages of energy sources, vitamins and minerals and certainly would
have a negative effect on both fecundity, fertility and probably longevity.
(You will not be able to do proper repair if you have shortages of key
nutrients.)  There is a scale in terms of dietary intake:
  starvation << calorie-restriction << sufficiency << abundance
And this must be measured across at least 4 different areas:
  energy-intake (calories), amino-acids, vitamins, minerals

Life extension by calorie restriction works when there are sufficient amounts
of amino-acids, vitamins and minerals and the energy-intake is restricted.
I would argue that in the wild all species evolved to conserve any essential
nutrient that could be in short supply and lost the ability to manufacture
nutrients which were in great excess in its natural food supply.  As a result,
when environmental conditions get "tough" (due to drought, migrations, etc.)
animals should experience a reduced energy-intake but have enough reserves
of essential nutrients or biochemical pathways which compensate by making
nutrients which are unavailable in the environment.  Under these conditions,
the body cannot afford to put resources into reproduction because the
nutrients required are unavailable or else providing them to offspring
would present a threat to the mother.

I suspect that most studies involving humans have a very difficult time
being matched with this theory because there are very few CR human
populations.  Most of the time we are in sufficiency or abundance
or less often in starvation.

It is clear that factors such as the education of women have a very
important impact on their fertility.  I would be interested in
knowing whether studies of nutrition on fertility in humans controlled
for the cultural/educational changes which may have occurred.
-- 
Robert Bradbury			uunet!sftwks!bradbury

Death is an imposition on the human race, and no longer acceptable
				Alan Harrington, The Immortalist (1969)
Newsgroups: sci.med.nutrition