Why do we eat foods even when we know they will keep us from losing weight? Getting to that answer means understanding pleasure and the body's physical response to it. Scientists have believed for years that the neurotransmitter dopamine, a chemical found in the brain, is the brain's "pleasure chemical," sending signals between brain cells in a way to reward a person for a particular activity. The precise details of this pleasure loop haven't been completely determined, but enough of it has been clarified to give us an idea of why the body commits us to actions that are against what we know makes sense for that body.
The neurons—nerve cells in the brain—that produce dopamine seem to activate just before the pleasurable activity is engaged. The timing of what comes first is still being worked out, but one leading theory is that our brain releases a certain amount of dopamine in anticipation of how pleasurable we expect the activity is going to be. The dopamine then becomes a motivator as it increases our energy and drive to participate in the pleasurable activity. The more pleasurable the activity, the higher the dopamine levels, the more vigorously we pursue and engage in the activity. If you don't find the activity as pleasurable as you expected, your dopamine levels decrease and you lose interest.
The brain's dopamine reward system can be extremely strong depending on the degree of pleasure one achieves. For example, take warm apple pie and vanilla ice cream. For many people, eating this dessert produces such a level of pleasure and satisfaction that they find it almost impossible to pass up the opportunity to order it when seeing it on a restaurant menu or being served to another diner. The dopamine response to the thought, sight, smell, and taste of the apple pie is overpowering, and despite great efforts to avoid the sugary dessert, they simply can't help themselves.
We've all had a craving—a strong desire to eat or drink something, so strong we can't get the thought of it out of our minds. Most people think of cravings as intense urges that gnaw at the body and mind until the desired item is consumed. But scientists aren't so sure where cravings come from or why they exist. One long-held belief is that when we are calorie starved or deficient of certain nutrients, we crave what we're missing, whether it's carbohydrates, fat, or protein. The craving serves as the body's alarm clock to let it know that the level of that particular type of fuel is getting dangerously low and it's time to do something about it—eat.
Another popular theory is that when we eat the right combination of fat and carbohydrates that have pleasurable tastes and textures, our body builds up a memory of satisfaction and seeks to repeat it in the future. In essence, the body craves those foods that make it feel good. Some leading nutritionists have even drawn the conclusion that cravings are connected to hormones. That theory says that as we age we become less hormonal and the frequency of our cravings diminishes drastically.