If you’ve ever promised yourself you’d stick to just one chip—or heck, even just one handful—but blown way beyond that, you know how often it is to stop eating salty food once you’ve started. The reason you keep dipping your hand back in the chip bag doesn’t just have to do with the flavor. (Whether you’re into chips or chocolate, find out what your food cravings say about your health.)
In one study in Frontiers in Psychology, researchers let rats choose from three different foods: standard chow, a mix of fat and carbohydrates, or potato chips. The rodents by far preferred potato chips over the other two options. If it’s not just the fat and carbs, what gives?
Potato chips are best known for two things: salt and fat. Studies have shown that eating salt triggers the release of dopamine, a chemical messenger that controls your brain’s pleasure center. Once your brain gets that first reward hit, it starts craving more.
In one Australian study, 48 adults could eat as much as they wanted during four different lunches. The pasta meals looked basically the same except for one tweak: the salt and fat contents. The sauce was either low-fat/low-salt, low-fat/high-salt, high-fat/low-salt, or high-fat/high-salt, and participants tried each one once over the four weeks.
No matter how much fat was in the food, volunteers ate 11 percent more calories and food when the sauce was extra salty, according to the results in The Journal of Nutrition. (Learn the 7 signs that you eat too much sodium.) With a high-fat sauce, participants ate 60 percent more calories, but not necessarily any extra food in terms of weight. Fat itself is high in calories, so volunteers were eating more calories with the same amount of food.
Normally, fat helps make a meal more satisfying so people don’t want to just keep eating and eating—especially when people are particularly sensitive to the taste of fat. (If you can’t stop eating, learn 8 reasons you’re always hungry.) When food is low in salt, it’s easy to practice self-control instead of overeating, says study author Russel Keast, Ph.D., professor of sensory science at Deakin University. “But when we add salt to that food, all of a sudden those controls are gone,” he tells Time. So fatty chips that didn’t have extra salt would be one thing. Once you add salt into the equation, though, your brain wants as much sodium (and dopamine) as it can get.
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