We, modern humans, have a tough time curbing our appetite. The reason for that is that our primitive ancestors, leading a life of hunters/gatherers (or scavengers, as recent research suggests) did not have a steady, predictable supply of food. So our physiology has evolved to store calories when we could get them, in the form of fat. The need was to maximize conservation of energy (or calories), and an elaborate system has evolved in the gut and the brain to accomplish that.

This state of affairs served our species well until relatively recently. When the industrial revolution arrived about 200 years ago, farms became more efficient and produced more food, people became more affluent working in factories and offices, being able to afford the cornucopia of food and drink. At the same time, work—and life, in general—demanded less and less effort (or expenditure of calories). The consequences are evident today on every street of the industrial world. Unfortunately, our metabolism has not been able to adapt to this relatively recent change in lifestyle. Such things require an untold number of genetic mutations and take thousands of generations.


Is there nothing to be done about it?

The only way we can change our metabolism is through drugs. So far, all the heavily promoted and hyped diet pills, which are basically attempts to change our metabolism chemically, have been either very limited successes or total failures. Fortunately, we are a species endowed with a high degree of awareness and the capacity to quickly adapt to changes in behavior. Remember Pavlov’s drooling dog? We are better. Being aware of what triggers our brain to send “hunger” signals allows us to counteract them through behavioral strategies.


The biological clock

No, this is not really a ticking clock; but, biologically speaking, a lot more powerful. A clock is neutral, it just keeps time. There is no inherent functional meaning to 3AM or 3PM. It is us who invests it with the meaning of afternoon or early morning. The biological clock, on the other hand, doesn’t only tell time, it gives time a meaning. For instance, around 6 PM, I get terribly hungry. Or around 6:30AM, I wake up regardless whether I got enough sleep or not. And when I travel across time zones, either to Europe or the Far East, my biological clock and my whole physiology still lives in California and is totally screwed up.

We can see then, that this clock actually controls much of the brain function. One of these functions is the sensation of hunger. I am used to eating breakfast at a certain time of the day, and if I don’t get it, I feel that something is missing, I am unhappy and miserable to be around, and I can’t function at peak performance. If you think about it, the clock didn’t just control hunger, it controlled mood (great omelet = happy; it’s 11AM and I haven’t had my breakfast yet = unhappy).

The nice thing about this all-powerful clock is that it can be trained to suit our whims. Try skipping lunch and the first few times will send you trawling for food the whole afternoon. But after a while, your need for lunch becomes less and less urgent until eventually you really don’t feel the need to eat in the middle of the day. But don’t carry it too far. I am reminded of one of my professors at UC Berkeley (who will remain anonymous for obvious reasons), who studied the metabolic effects of calorie deprivation in the German cockroach (Blatella germanica; and I am not making this up). He slowly habituated the critters to a progressively lower calorie diet. One morning, he came to the lab and was dumbfounded to find his meticulously habituated cockroach colony totally, irreversibly dead. Theories as to the causes ranged from the sublime to the ridiculous. To my simple-minded suggestion that they may have died of run-of-the-mill starvation, he responded plaintively, “but they have already got used to it…”


Sight and smell

Why are the French such foodies? My theory de jour is the presentation. When we walked in the market in Beijing and saw row after row of hanging Peking ducks at the butcher shops, I was mildly disinterested. But when they wheeled in the duck in a fancy restaurant, the thing looked irresistibly delicious and we devoured the whole thing. How do you think Ray Croc made McDonald’s such a success? He stood outside a small hamburger diner and took in the smells. He immediately knew that he stumbled upon a winner, bought the restaurant, and its formula for Freedom (a.k.a. French) fries and hamburger patties, and the rest is, as they say…fat kids with diabetes. Both the rhinencephalon (or the smell center) and the visual cortex communicate with the hypothalamus, the area in the brain that controls hunger, through extensive neural connections.


Don’t eat when you are cold

One of the important functions of our physiology is to maintain normal body temperature. For instance, the shivering response to cold is a way for the body to raise its temperature. Metabolism creates heat, and when we are cold, the normal response is to eat more and more frequently. That’s why we tend to eat more in the winter (and, alas, gain more weight) than in the summer. Can you imagine yourself being ravenous on a 100° day? All I can think of is crushed-ice margaritas.


What can we do?

The answer is…a lot. The biological clock and the relationship between smell, sight, and hunger are all subject to habituation—or more plainly, to our will. This is literally the old “mind over body”, and all we need is the will and the persistence.

And yes, don’t forget to heat up the house before you sit down for dinner.

Dov Michaeli, MD, PhD
Dov Michaeli, MD, PhD loves to write about the brain and human behavior as well as translate complicated basic science concepts into entertainment for the rest of us. He was a professor at the University of California San Francisco before leaving to enter the world of biotech. He served as the Chief Medical Officer of biotech companies, including Aphton Corporation. He also founded and served as the CEO of Madah Medica, an early stage biotech company developing products to improve post-surgical pain control. He is now retired and enjoys working out, following the stock market, travelling the world, and, of course, writing for TDWI.