Tuesday, August 17, 2010

Bigger and Slower

     Bigger and Slower

     A recent study in Annals of Neurology, a well-respected medical

journal, described an inverse relationship between fat and brain size

in healthy middle aged adults. In other words, the fatter (especially around the abdomen, i.e. visceral fat) the subjects, the smaller smaller their brain. Bigger and slower. This is new. We have known

that obesity, particularly in midlife, is associated with an increased risk

of dementia (memory impairment) and Alzheimer’s disease. Studies have also demonstrated that

different fat compartments carry different metabolic risks, such that abdominal fat

is much more damaging than subcutaneous fat (the fat underneath your skin

throughout your body). So this is another piece of evidence, and a particularly graphic

one, that excess fat can really do us harm. We must ask ourselves why fat, that

supposed inert energy depot, is able to wreak such havoc.

Once again, we must go back in time and look at the environment

that selected for our genetic makeup. One of the most essential factors

in the survival of any organism is the acquisition of food, energy. It would make

sense for an animal to have sophisticated connections between

energy status, metabolic rate regulation (how fast we burn fuel) and reproductive functions.

If a famine is beginning, the animal’s intake decreases, it’s fat stores

dip, and that in turn sends a message that slows metabolism and shuts down

reproductive activity. This would provide the greatest chances of not only that animals own survival,

but also that of its offspring. So it should not surprise us that our fat

stores, the index of external conditions, send commands to every regulatory

system in our body.

THE PROBLEM: We do not live in the environment that formed our genome.

We are adapted to a world that disappeared long ago. We were hunter-gatherers

until the agricultural revolution 10,000 years ago, a tiny tick in time insufficient for

significant genetic adaptation. This was the the first huge shift in our diet, introducing

grains and domesticated meat, and dramatically narrowing the variety of plant foods.

We were much better nourished as hunter-gatherers than farmers. But at least we remained active.

The industrial revolution was the coup de grace. Our diet continued to

distance itself from its origins with ever more processing, and we no longer

had to move to eat.

Cut to the contemporary equivalent of the savannah, your local strip mall. You drive up to

the window and tell some youngster on minimum wage how many calories you want. This is

a far cry from persistence hunting where we chased down game until they died of

heat exhaustion in order to have dinner. (By the way, it suggests that we are

programmed to take a walk, if not a run, before dinner, not after.) The glut of calories

in conjunction with minimal or no physical activity, is incomprehensible to

our genetic makeup. We are getting big and slow. We have become our own

most dangerous predator.

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