Animals—and people—learn to link food sweetness and viscosity with high caloric content. Animal studies in the July International Journal of Obesity suggest that regularly ingesting sugar substitutes or artificially sweetened drinks might reprogram individuals so that they can no longer judge the caloric impact of truly sugary snacks.
In one test, Terry Davidson and Susan Swithers of Purdue University in West Lafayette, Ind., provided adolescent rats with sweet drinks and all of the food they wanted for 10 days. Some animals were given only sugared drinks; the rest received drinks sweetened with saccharin alternating with drinks containing sugar. At the experiment’s end, the animals fasted for 12 hours before receiving a 5-calorie chocolate snack, a substantial treat for a young rat.
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An hour later, the researchers offered the animals a full meal and tallied calorie consumption during the next 60 minutes. Rats that had gotten only sugared drinks ate another 4 calories, whereas those that had alternately downed sugared and artificially sweetened drinks pigged out on a whopping 15-calorie repast.
The data suggest that “if you confuse the relationship between sweet and calories,” the fight against overindulgence becomes more difficult, Swithers says. “We may have to learn to gauge energy intake in ways that require more of our attention.”
In a second test, mature rats received a high-calorie chocolate snack every day. For half of the animals, the snack was as thick as pudding; for the others, it was the consistency of milk. Both snacks had the same calories. Over 1 month, animals receiving the milklike supplement consistently gained a little more weight than the others did. This suggests, Swithers says, that “drinking a beverage may produce more weight gain than consuming the same calories in a more solid form.”