Since Tom’s doing a little amateur evolutionary theory, I might as well join in. Herein, I present my theory of Darwinian dieting.
Several months ago, I embarked on a new exercise and diet program. I wasn’t fat – indeed, most would have called me skinny – but I had a little spare tire that I wanted to shed. I actually overshot my target, losing more weight than I had planned. In the process, I learned a lot about how my body works, and here’s one of the things I learned: that eating is instantaneously addictive. That is, the very act of eating makes me want to eat more. Even if I don’t start out hungry, if I start eating, I don’t want to stop. Fortunately, the addiction is short-lived: if I refrain from eating for 20 to 30 minutes, the cravings will cease.
Knowing this fact has helped me maintain my diet. At each mealtime, I serve myself a fixed portion. When I’m finished, I will inevitably want to keep eating. So I’ll say to myself, “Wait half an hour. If you’re still hungry then, you can eat more.” But most of the time, the hunger is gone half an hour later.
A cousin of mine tells me she has a similar trick: when ordering at restaurants, she asks the waiter to put half her meal in a doggie bag before she eats. She finds it easier to resist eating the second half when it’s shielded from her vision by the packaging.
What makes us want to keep eating when we’ve already had enough? I blame evolution. In the wild, if a creature finds a food source, it makes sense to consume the food until it’s gone. Why? First, because any food left behind will probably get eaten by other animals. That means food can’t effectively be saved externally, so it should be saved internally as fat. Second, food sources are scarce; there’s no telling when another good food source will be found. These factors combine to create a selective advantage for creatures with an internal drive to eat all the food available. But perpetual hunger, even in the absence of food, would distract creatures from other necessary tasks. So natural selection has equipped animals with a contingent hunger impulse that manifests in the presence of food.
Of course, neither of those conditions hold now. Food can be saved for long periods of time and secured against the predation of other animals, and food is cheaper than ever before. As a result, our genetic makeup is suboptimal in present conditions. But knowledge of that genetic makeup gives us the power to manipulate ourselves and obtain greater control over our impulses. My “wait half an hour” trick takes advantage of the hunger impulse’s being contingent on the recentness of eating, while my cousin’s “early doggie bag” trick relies on the hunger impulse’s being contingent on the visible presence of food.