Diet
can strongly influence how long you live and your
reproductive success, but now scientists have discovered
that what works for males can be very different for
females.
In the first study of its kind, the researchers
have shown that gender plays a major role in determining
which diet is better suited to promoting longer life
or better reproductive success.
In the evolutionary "battle of the sexes",
traits that benefit males are costly when expressed
in females and vice versa. This conflict may have
implications for human diet, aging and reproduction,
says a team of scientists from UNSW, the University
of Sydney and Massey University.
"When it comes to choosing the right diet, we
need to look more closely to the individual, their
sex and their reproductive stage in life," says
Associate Professor Rob Brooks, Director of the Evolution
and Ecology Research Centre at the University of New
South Wales. "It may be, for example, that women
in their child-bearing years need a different diet
to those who are post-menopausal.
"It also underlines the important lesson that
what we want to eat or, if you like, what we're programmed
to eat, is not necessarily best for us." The
researchers are conducting long-term studies on Australian
black field crickets and have discovered that the
lifespan of both males and females is maximised on
high-carbohydrate, low-protein diets, they say in
the latest issue of Current Biology.
But reproductive success differs dramatically between
the sexes when the carbohydrate-protein balance is
changed: males live longest and have the greatest
reproductive success with a diet that favours carbohydrates
to protein by eight-to-one, whereas females have greatest
success when the ratio is just one-to-one. Given a
choice, however, females eat only a small amount more
protein than males. The shared ability to sense and
choose food dooms both males and females to eat a
diet that is a compromise between what is best for
each sex.
"Male and female crickets maximise their fitness
on different diets," says UNSW's Dr Alexei Maklakov,
the study's lead author. "Despite that, the dietary
preferences of the sexes are very similar. Instead
of selecting foods in a sex-specific manner, males
and females select 'intermediate' diets that are less
than optimal for both sexes.
The researchers believe the sexes share most of their
genes and this fact can constrain the evolution of
sex differences in traits such as diet choice, because
many of the same genes are likely to be responsible
for trait expression in both sexes.
Significance for humans -- "Men and women invest
differently in reproduction, a difference that is
even more marked than that between male and female
crickets," says Rob Brooks. "Think of the
tremendous amounts of energy and protein required
of a mother in carrying a baby to term and breastfeeding.
We also know that men and women need to eat different
diets - think of the careful attention we pay to what
expectant mothers eat.
"What men and women need to eat might be more
dramatically different than we had realised. However,
men and women eat very similar diets and our results
suggest that our tastes and food preferences could
be a shared compromise, as they are in crickets."
