The reward system is what motivates you to get food and put it to your lips, every time you eat. When scientists shut it down in mice, they completely cease eating. The hedonic system influences how much you eat once you begin a meal… Together, reward and hedonic circuitry in the brain determine in large part how often you eat, what you eat, and how much you eat, and this is influenced by the attributes of the food that’s available.
“[...] influenced by the attributes of the food that’s available” is a phrase important to parents. In plain English — no junk food in the house! The reward system, the author suggests, offers a benefit to parents, because it:
[...] allows children to learn to like vegetables — which are low-calorie, often bitter foods that are initially unpalatable — if they’re repeatedly paired with fat, salt or some other desirable quality. The reward system does the same thing with foods/beverages that contain drugs, such as coffee and beer, gradually making bitter fluids palatable and then delicious.
The brain’s reward system is one of the checkpoints where good food is distinguished from bad food. In nature, it’s not totally reliable. It is possible to eat something that looks and smells and tastes delicious, but turns out to be fatal.
Or, in the example Dr. Guyenet uses, it’s possible to eat something that tastes kind of yucky, like a strong cheese, but the reward system recognizes the arrival of densely packed life-giving calories, plenty of bang for the buck. So that overrides the initial negative reaction to the flavor, and an acquired taste is born.
Whether or not a person finds a particular substance palatable depends on inborn preferences shared with all humans (liking sugar, for instance) and family genetics, and early exposure, and cultural attitudes, and state of health. And then, thanks to the hedonic system that lights up the brain a few seconds or minutes after the substance is ingested, palatability is learned, because the taste is now paired with this little explosion of fun in the hedonic system.
The mechanism is so strong, in fact, that a person doesn’t even have to taste a milkshake, only see a picture of one, and the brain lights up. So why isn’t that enough? If the goal is to spark some brain cells, and if just thinking about a milkshake accomplishes that, then why do we still go ahead and eat the darn thing? And all those other “bad-decision” foods too?
Dr. Guyenet lists the qualities that cause the reward system to fall in love at first bite:
Calorie density, fat, starch, sugar, salt, free glutamate (umami), certain textures (easily chewed, soft or crunchy, solid fat), certain flavors, an absence of bitterness, food variety, and drugs such as alcohol and caffeine.
In a natural environment, the theory goes, it was beneficial for humans to like all those things, and to recognize and realize that they liked them, even if they didn’t understand why. And throughout most of history, in most places, it wouldn’t matter how much a person loved chocolate-covered bacon, they probably would not be getting any, so their proclivity for it couldn’t do much harm.
We need senses that tell us, “This is good to eat.” But, even in primeval nature, the reward system is not a foolproof guide to what is good for us. In the toxic-food environment we live in today, everything is haywire. The exaggerated combinations of desirable qualities that are engineered into junk foods simply hijack our built-in reward systems and lead us far, far astray.
Dr. Guyenet’s point is:
… [T]he brain’s hard-wired mechanisms for regulating food intake and fat mass in a natural environment are not sufficient to protect against modern hyper-palatable and hyper-rewarding food… Returning to a diet of simple home-cooked food, made from minimally refined ingredients, would probably stop the obesity epidemic in its tracks, although it would not be enough to return all currently obese people to a lean state.
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