by
Mark Sisson
Mark’s Daily Apple

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A few months
ago, I addressed the role gender
plays in how we respond to intermittent fasting. That post sparked
a great discussion, and I’ve since received a fair number
of emails from readers eager to learn other ways in which gender
plays a role in our health and nutrition. One email in particular
set me off on a round of research. So, a hat tip to you, Winifred,
for giving me something to think, learn, and write about. I hope
everyone finds it to be helpful.

As you may
know, women and men store and metabolize fat differently from each
other, and a 2008 paper (PDF)
reviewed the evolutionary reasons for these differences. Here’s
a summary of their findings and few other noteworthy factoids:

Women carry
more fat than men. They are better at storing fat than men. Moreover,
when women store fat, they do so in different places than men. They’ll
preferentially store fat in in the hips, butt, and legs, whereas
when men gain weight, it usually goes to the upper body (hence why
you see massive beer bellies atop stick legs). Furthermore, when
both men and women store upper body fat, men are more likely to
develop visceral fat – the abdominal fat associated with metabolic
syndrome – while women
are more likely to develop subcutaneous fat.

On women, body
fat seems to be healthier and less problematic. The characteristically
female lower body “gluteofemoral fat” is actually
a strong sign of metabolic health, whereas abdominal fat is
not. In men, high body fat levels correlate strongly with insulin
resistance, while this relationship is much weaker in women (probably
because of their lower tendency to store visceral fat).

Women burn
fat differently than men. Upper body fat goes first, while lower
body fat tends to stay put. Except during pregnancy and lactation,
when the lower body begins to give up lower fat stores far more
readily. Interestingly (and not by coincidence), women tend to preferentially
store the long chain omega-3
fatty acid DHA – the one that’s so important to
the baby’s development during and pregnancy – in
their thighs.

Women make
more triglycerides
than men do, but their serum levels are similar. This indicates
that the fat is being taken back up into adipose tissue at a higher
rate in women than in men.

Women are better
at burning fat in response to exercise. During endurance exercise,
they exhibit lower respiratory exchange ratios than men, which indicates
more fat burning and less carb burning.

Women are better
at converting ALA into DHA, and they also tend to have more
DHA and AA circulating throughout their serum than men, who have
more saturated and monounsaturated fat.

These differences
in fat metabolism aren’t
seen in isolated muscle cells of men and women, which isn’t
really surprising. We’re made with the same basic building
blocks; we just run on different software. The differences are systemic
and hormonal.

Why
does this sexual dimorphism in fat metabolism exist?

Well, the name
of the game in evolution is reproduction, and reproduction is far
more nutritionally expensive for women than it is for men. I don’t
think I have to spell out why – for a man, the reproductive
process is a brief moment in time, a half tablespoon’s worth
of effort; for a woman, the reproductive process lasts the better
part of a year and represents a significant drain on nutrient stores.
As such, women are “designed” to hold onto said nutrients
because, as far as evolutionary fitness is concerned, her primary
purpose is to feed, nurture, and cultivate an entire other human
being inside her body for nine months. Think about that for a second:
women have to create and support another life inside their bodies.
They have to provide the food, the water, and the shelter. If something
goes terribly wrong in the “outside world,” that nutrient
flow to the fetus could be interrupted, thus putting her evolutionary
purpose at risk.

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August 25, 2012

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© 2012 Mark’s Daily Apple

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