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Fatter folks, sicker bay

For insight as to why we're having trouble restoring the Chesapeake Bay, I'm reading "The Evolution of Obesity" by medical researchers Michael L. Power and Jay Schulkin.

It's an illuminating look at how we got so fat. It's epidemic — more than a fifth of the world's population is overweight or obese.

In the United States, obesity-related health problems are soaring. The standard revolving door has gone from six to eight feet, and hauling our ampler butts costs airlines a quarter-billion more in fuel than it used to. The proportion of normal-weight Americans is at an all-time low.

But what's a fat book got to do with the state of the Chesapeake Bay? Around the world, coastal waters have gotten fat. "Eutrophic," or overfertilized, is the technical term, from the Greek for well-fed. Dead zones like the bay's occur in more than 40 regions of the world.

It's intriguing to compare graphs tracking these declines to graphs in Messrs. Power's and Schulkin's book that track the U.S. upsurge in fatness.

Roughly, human obesity and estuarine dead zones both began to proliferate around the 1970s. Mindful that the body is not an estuary, I won't put too fine a point on this coincidence. But today's "obesogenic" environment, as the book calls it, seems to be a useful lens for connecting human ways and the ways of bays.

"The Evolution of Obesity's" authors marshal medical science and evolutionary biology to show how impressively adapted the human organism is to avoid underweight and starvation.

Our bodies can suppress appetite when food is scarce; they also become more efficient at maintaining body mass in lean times; and we're geared to glom onto and make the most of "calorie dense" foods full of fat or sugar.

And why not? For all but the last ticks of the evolutionary clock, calories were hard to come by, and calorie burning — physical exertion — was hard to avoid.

Fat was good for other reasons. Human babies are naturally among the fattest of mammalian species, close behind seal pups. The reason appears to be that fat, with 10 times the energy storage of muscle, fuels development of our big brains, themselves about one-third fat.

And fat, up to a point, helps the body fight off pathogens, which became a problem once humans began living in settled communities, close to one another and to animals.

The authors show that we like the feel of fat in our mouths. Sugar, too, has always been our friend — so much that a bird in Africa, the honeyguide, has evolved to follow honey-seeking humans to the beeswax it eats.

The bay also evolved elegantly to do more with less. The watershed for thousands of years was thick with forest, bemucked with beaver ponds and other wetlands, resulting in river flows that were not just clean but lean in the nutrients that fuel aquatic food webs.

The Chesapeake thrived fabulously on this diet. Its shallowness, its two-layered flows of freshwater riding atop salt, its structures of filtering shellfish and burrowing worms and clams, its vast grass beds that could absorb and rerelease nutrients — all of this and more enabled the bay to retain, recycle, and recycle again whatever food it could get. Think of it like swishing a tasty drink around in your mouth for a long time, extracting all of the goodness.

Both humans and estuaries in recent decades have entered a world that is nutritionally abundant beyond anything they knew. And though well-adapted to cope with less, neither man nor bay ever needed mechanisms to cope with too much — one reason the authors of "The Evolution of Obesity" are skeptical that drug companies will isolate a magic molecule or gene to limit getting fat.

The appetites that have larded today's humans have sped up the bay's eutrophication. A diet rich in meat means extensive, intensive, heavily fertilized and fertilizer-leaky agriculture, a major cause of dead zones worldwide.

Even heartier appetites for fossil fuels have fed the bay far too much fertilizing nitrogen, via air pollution.

With so much energy available to work for us now, we humans must make an effort to get the exercise that used to automatically burn fat.

While the bay never literally exercised, its wet and forested watershed used to process nutrients far more vigorously, "denitrifying" them back into the atmosphere or burying them in sediments. Now they just mainline off pavement into the bay.

Nowadays, "thin" is in for humans, as "green" is for the environment. Yet the trends still don't match the images — and may never, unless we comprehend where we came from.


Copyright © 2015, Chicago Tribune
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