The process of evolution required over a billion years to evolve a brain that could forage successfully for food and multiply itself into more brains. Yet, the snack food industry required only a few decades to undermine everything and fool your brain into eating more calories than your body could ever possibly need.
The brain receives numerous signals from the gut and body, such as the molecules ghrelin or orexin that encourage us to eat. When we are satiated, or our body contains adequate amounts of stored energy, our brain receives signals that our stomach is distended, or the molecules cholecystokinin or leptin are released into the blood, or our brain is ultimately informed about how many fat cells we possess and how full they are of fatty acids. Thus, we are gently encouraged to stop eating. The physiological controls over energy consumption are complex and often compete with each other for your brain's attention. Given this complex web of influences that have taken so long to perfect you might predict that we are always in complete control of our diet. Obviously, this is rarely true. But why? What could possibly override this complex, highly sophisticated body chemistry? The answer is simple: the brain itself.
It appears as though our brain can easily override the body's internal and external signals about when to stop eating; this is especially true if the first few bites of the meal are particularly tasty. This is why restaurants often put all of their best efforts towards presenting an outstanding appetizer so that we are more likely to rate their mediocre main dishes more favorably.
The decision process for starting to eat is rather simple. First, see the food and eat the food; second, keep eating until it's gone. In contrast, the decision process for stopping eating is far more complex. Is there more food left? Are others competing with me for the food? Our brains are nearly incapable of estimating how many calories we've consumed and that no matter how intelligent a person might be, or how motivated to lose weight a person might be, that we are all still vulnerable to overeating. We are compelled by our genetic legacy to eat whatever and whenever possible. Not only that, we tend to subconsciously prevent others from taking our food source. According to neuroscientists we defend our access to tasty food when it is within easy reach and is at risk of being consumed by other humans.
In addition, our brain tends to associate positives together and then gives us the impression that the two things are related more than by a simple correlation. We see the word "organic" on foods and believe that it must be healthier; we assume that a wine from France must be of higher quality than one from Ohio; we assume that we can eat more of something that is labeled "low-fat." The problem is that our brains never evolved the need to limit how much we eat. Finding food, any food at all, was one of the most important things brains evolved to do. Food meant survival and the chance to produce more offspring. Today the nature of eating, and food labeling, is changing faster than our brains can adapt.
With the odds stacked against us what can we possibly do to prevent our brain's tendency from making us overweight? Part of the answer lies in understanding the importance of the italicized lines above. Therefore, place smaller portions in front of you; never eat at buffet tables; try eating alone.
© Gary L. Wenk, Ph.D. author of Your Brain on Food (Oxford, 2010)