02/15/2013 06:38 pm ET Updated Apr 17, 2013

The PRH (Personal Responsibility for Health) Chronicles, Part 4: Polar Bears in the Sahara

Please also see the PRH Chronicles part 1, part 2, and part 3.


Mik-tal and Bo-tu are adapted to their environment, one in which demands for physical activity are constant and high, and food nearly always in short supply. In such an environment, metabolic efficiency is essential to survival. We still have the very metabolism that our ancestors developed, over a period of 4 million years, in a world of limited food and constant physical activity. Our ancestors' traits -- an innate preference for sweet foods and a natural tendency to crave salt, a preference for dietary fat, the tendency to store excess calories as fat quite readily and release them much more slowly, a strong compulsion to binge eat -- all defend us against too little food. We have no natural defenses against too much food. Yet we find ourselves in a world with food available in constant abundance, and physical activity an option if not an inconvenience, and very rarely a necessity.

There is something going on with us and our environment that we fail to see in ourselves, yet see readily in other species. A connection, a bond. The notion that we are not truly separate from nature, but actually belong to it, and have a home within it.

As do all creatures. The bond between polar bears and their environment, for example, is self-evident, undeniable. Everything about the bears, from the shape of their bodies and heads, to the layers and coloring of their coat, is designed to conserve heat. And so they thrive almost beyond imagining in the Arctic, one of the earth's harshest environments; polar bears have been found swimming in frigid water, 200 miles from the nearest land.

But they thrive only in the harshest of environments for which they are adapted. Take these magnificent survival machines and put them elsewhere, such as beneath the Sahara's blistering sun, and they would surely meet their demise. Despite the fact that other creatures thrive in the desert, the polar bear is simply not designed to do so. Heat conservation leads to survival when heat is scarce, and death when heat is overly abundant. But a polar bear can't stop being what it is or doing what it does to satisfy a change of scenery. And so, the environment makes or unmakes the bear, as it does for almost every creature on the planet.

Except us? On the surface, it may appear so. For we have overcome so many of nature's challenges, it is tempting to think we are immune to all the rest. Our resourceful intelligence has enabled us to deal expediently with heat and cold, draught and deluge. Yet while this has concealed the hold nature has on us, it has not freed us from it. Michelle can shut out the morning chill by closing a window of her climate-controlled house, but she seems powerless to resist the effects the modern environment has on her waistline, helpless in a losing struggle with her cravings.

Just as polar bears conserve heat, our ancestors conserved food energy. And so do we. But like polar bears undone by their ability to store heat when heat is suddenly abundant, we find ourselves undone by our metabolic efficiency in a world of constantly abundant food. If Michelle and Peter are Mik-tal and Bo-tu, then they are as ill-suited for the modern world as polar bears are ill-suited for the Sahara.

Like other species, ours lives in the modern world with prehistoric genes, prehistoric tendencies. Pronghorn antelope that race across the plains of Colorado and Wyoming are beautiful to watch, but to zoologists, they pose something of a mystery. They can run up to 40 miles per hour, and sustain their top speed for more than four miles, even though no existing predator can come close to catching them. Thousands of years ago, however, such predators -- long-legged wolves and a North American hyena -- did exist. So the pronghorn continue to run for their lives -- from ghosts. They share the genetic makeup of their ancestors, and thus remain what their past required them to be. And so do we.

We, too, have a natural environment. And a world of fast-food drive-through restaurants, fax machines, escalators and email is not it. The nutritional environment we live in is toxic to us. The effects of that toxicity are rampant chronic disease and epidemic obesity. In trying to choose fruits and vegetables over chocolate and cheese, you are fighting your own metabolism, engineered to preserve you through periods of famine.


-The PRH Chronicles will continue...

Dr. David L. Katz;

For more by David Katz, M.D., click here.

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