The Evolution of Human Gluttony

(A longer discussion of gluttony in animals and human can be found in my book.)

Gluttony is the overindulgence and over-consumption of food and drink and its something pretty much all of us are guilty of from time to time. We all love to eat. We especially crave rich, calorie-packed foods. Knowing that we “shouldn’t” often makes no difference at all. How often has your willpower collapsed at the sight of a scrumptious and moist chocolate cake? Our drive to eat goes way beyond basic hunger.

I think I speak for pretty much everyone when I say that if there were a magic pill that would allow me to eat anything I wanted in unlimited quantities and not suffer any weight gain or health risks, I would eat about six gigantic meals a day. And pecan pie. Lots of pecan pie.

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There is a drive within all of us to eat, eat, and eat some more. What’s worse is that this drive seems pretty well focused on foods that are horrible for us. When was the last time you had an intense, mouth-watering craving for brussels sprouts? At our most basic level, we are built to crave high-fat, high-sugar, and high-protein foods. Sure, many of us grow into an appetite for more healthy foods and learn to shun the empty calories of milkshakes and soda, but if you believe that is the result of anything other than conditioning and training, you are kidding yourself.

The next time you see someone smugly sticking their nose up at dessert or claiming to not enjoy fried foods, you can be satisfied knowing that person is either lying or that this attitude is the result of years of painful self-denial and emotional training. If children exhibit a more basic form of human emotions, their appetite for sweets and aversion to vegetables speaks for itself.

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Gluttony is a feature we share with pretty much all animals. Anyone with dogs or cats knows how they can gorge themselves on treats, meat, and other rich and savory foods. We have to carefully regulate the diets of our companion animals or else they will become overweight very quickly. The same is true for laboratory animals, be them rats, mice, rabbits, fish, monkeys—you name it.

Zoo animals, too. Great care has to be taken to select their diet—not just to include the diversity of food that they need to be healthy, but to regulate their intake so that they do not become morbidly obese. In sum, all animals, including and especially humans, if left to their own devices, will overeat to the point of extreme obesity. Why on earth is that?

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Contrast that with the seemingly contradictory fact that you almost never encounter obese animals in the wild. Animals in their “natural state,” that is, the environment they are adapted to through thousands of years of evolution, are most often trim or even skinny. When we put them in an artificial habitat, they will immediately balloon up if we’re not careful. Why would this be? Could it be that the artificial nature of the simulated environment just isn’t right for them?

Indeed, it was previously thought that the stress of captivity caused hormonal changes and nervous overeating. It turns out that that doesn’t seem to be the main issue. You might also guess that the lack of proper physical activity and exercise is the culprit. Nope. Plenty of experiments and anecdotal experience have disproven both of those hypotheses. So why do animals stay skinny in the wild but become obese in captivity?

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The answer is a little disturbing. It turns out that animals in the wild are probably living in a near-constant state of starvation and intense hunger. Life on earth is a pretty difficult experience for most animals. Life has been bustling on our planet for at least 3.5 billion years, and the animal kingdom emerged at least six hundred fifty million years ago. That’s ten times longer than the amount of time that has past since the last dinosaur died. During all this time, the proliferation of animals has allowed them to fill virtually every possible niche, where they experience intense competition with each other.

In other words, the great majority of animals in the wild live their lives teetering on a knife’s edge between survival and death. There simply isn’t enough food to go around. The fact that all species tend to produce far more offspring than can possibly survive was one of the first key realizations by Charles Darwin, leading him toward his discovery of natural selection.

What does this have to do with gluttony? Well, because animals are locked in a vicious struggle for survival, they are wired for intense hunger; they seek food essentially all the time and will consume every last bit that they can. After all, who knows how long it will be before they get another chance. Only by gorging on food when it does become available do animals get the best chance of surviving to the next meal. A lion will eat fifteen pounds of meat in a single sitting; a snake will eat a meal that can nearly equal its own body weight. US President Teddy Roosevelt told a tale of a school of Amazonian piranhas devouring an entire cow in minutes.

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Humans are no different. We have a drive inside us to eat at every opportunity. As soon as our stomach empties, we want to eat again. Fruits and vegetables will do if nothing else is available, but we really want the good stuff: high-fat, high-calorie foods. Those are the foods that are most essential for surviving for days and weeks when food may not be available. The problem is that nowadays, food is available to us constantly. Our bodies aren’t built for that.

Sensible eating decisions and disciplined restraint aren’t part of our inborn psychological toolkit. Nowhere in the animal world is willpower or self-denial important for survival. Today’s era of ready access to rich foods is a new experience for Homo sapiens, and there hasn’t been near enough time to expect a change in our biology because of it.

It should be noted that it was previously thought that our relatively sedentary twentieth-century lifestyle was mostly to blame for the recent increase in obesity seen in Western populations. The idea was that, in previous generations, much more of the population earned their living through physical toil, and, prior to electronics, most recreation was physical. While these two phenomena do probably play some role, the idea that decreased physical activity is chiefly responsible for the recent obesity epidemic is now falling out of favor. The availability of rich foods and our resulting calorie-rich diet really seem to be the main culprits.

For the masses, it’s only been a couple hundred years that rich food has been this readily available, and that is only in the developed Western world. Before the industrial revolution, only an elite few could eat rich foods every day, and the poor wretches were not much better off than animals in the wild. Indeed, being stout or plump was a sign of aristocracy and privilege until very recently.

We are now surrounded and bombarded with high-calorie foods, which goes against millions of years of evolution that have trained us to overeat whenever possible. Overeating was a great strategy when it was only rarely possible anyway, but now we are able to do it every day, multiple times. For most of us, our feeble willpower is simply no match for our physiology. As far as our bodies are concerned, at every meal, we are pounding on the energy storage, as if for a long winter when we may barely eat at all.

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It’s even worse than that. In addition to a tendency to eat, eat, eat, and choose energy-rich foods, our bodies are also built to adjust our metabolism and fat deposition patterns in order to gain weight easily and lose weight difficultly. Yep. Anyone who has struggled with weight loss can tell you this. Weeks and weeks of dieting and exercise results in negligible weight loss, while a weekend eating binge can pack on a few pounds just like that.

This is not an illusion caused by our cynical human tendency to see the glass half empty. Our bodies really do adjust our baseline metabolic rate in order to prevent weight loss and promote weight gain. This is accomplished by ramping down our “extra” uncoupled thermogenic energy expenditure when calories are being restricted and by immediately capturing any surplus calories in our diet and locking them down as fat deposits. Screw you, human body! In fact, most dieticians agree that exercise alone is ineffective for weight loss and can sometimes do more harm than good. It stimulates our appetites in proportion to any calories burned.

Why are our bodies so impossible when it comes to weight management? Once again, it’s because we are built to withstand a life of famine and starvation. For nearly all of our evolutionary history, obesity, heart disease, and weight-related diabetes were essentially nonexistent, so we didn’t evolve many defenses against them. On the other hand, starvation was a daily threat. Everything about our infrastructure for energy metabolism is reflective of that. In fact, that’s exactly why heart disease and obesity are so common now—our metabolisms are poorly adapted for the food climate that we currently live in. The current Western diet is so mismatched to what our bodies were designed to cope with that most of us are “fat, sick, and nearly dead” (the title of a popular documentary on the subject).

Just to end things on a slightly more uplifting note, I should remind everyone that healthy weight management is still possible, even with bodies that are seemingly built to thwart us. Fad or crash diets never work over the long term. Hundreds of studies have proven that. Instead, healthy and sustainable eating styles must be adopted permanently. Opt for more fruits and vegetables, less desserts and meat. More whole and raw foods, less processed and sweetened ones. Cut out the soda, and trade out fruit juice for vegetable juice. Combine high-protein and high-fat foods with high-fiber and low-density foods. In other words, have your steak or hamburger, but keep it small and have veggies or salad as a side instead of fries or potato. Try to eat more slowly and drink plenty of water as you do. Have whole fruits for dessert instead of cake or ice cream. Treat yourself on occasion, but keep it rare and the portions small. Walk and cycle whenever possible, and take the stairs instead of the elevator every day. Throw in some regular cardiac exercise, and you have a recipe for healthy energy management. It’s not always easy, and sacrifices must be made, but most people find that the resulting “high” of feeling healthy and energetic makes the new life pattern easier to maintain. (Or so I hear.)

-NHL     (@nathanlents)

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