Eating Junk Food May Block Signals to Stop Overeating

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Self-control doesn’t come easily when it comes to eating junk food. While many of us typically blame ourselves for weak willpower, a new study this week indicates the food we eat may actually change our brain in a way that makes it harder for us to move on to other foods when we’ve had enough of the junk.

Previous research has shown that many animals, including humans, have a built-in mechanism for balancing their food intake. When a person eats a lot of a certain type of food, their brain starts to decrease the appeal of the taste of that food. As this happens, a person tends to stop eating that food and moves on to something else, naturally balancing out their diet. But there are ways around this. Prior studies had indicated that eating a lot of rich, high-calorie foods could weaken this barrier in favor of the reward these tasty treats can provide, but no research had formally confirmed this hypothesis.

For this study, researchers fed a group of rats healthy food and gave them the opportunity to sample periodically from cherry and grape sugar water. For several trials, researchers would limit the availability of one flavor so that rats could only drink either cherry or grape. When the other flavor became available again, the rats preferred that flavor over the one they’d had too much of. This change in taste to avoid overindulging in favor variety of flavors consumed was expected based on previous research.

Researchers then switched some of the rats to a diet of junk food that included pie, dumplings, cookies and cake and allowed the rats to indulge and gain weight. They then repeated the earlier experiments where they gave a lot of one flavor and then made the other available and looked for differences between the healthy and junk food rats.

They found that the rats on the junk food diet no longer self-regulated in the way they had before. They continued to sample from both flavors of sugar water regardless of how much they had consumed in the past, whereas the healthy diet rats continued to show a preference for whichever flavor they hadn’t had recently. Even when the junk food rats were switched back to a healthy diet for a week, they continued to consume both flavors even if they had overindulged on one or the other.

It’s important to remember the study was done in rats, not humans, and that the story may be different for people. But the study shows us that the food we eat may be changing the way our brains approach variety in our diet. Even when we have built-in behaviors to avoid eating too much of one thing, the reward of sweets and rich foods might be overpowering our tendency toward variety. Additionally, that change might apply to the way we approach all food, making us less motivated to seek out variety if we’ve been overindulging in other areas.

(Press Release)