When we go on a diet, we often add artificially sweetened drinks and low-calorie dishes to help us meet our goal, but we may be tricking our metabolism into piling on even more weight and triggering diabetes, says a new study from Yale University.
The sweetness in naturally sweetened foods tells the body the food contains energy, and the sweeter the food, the more energy it usually contains. But when a beverage is either too sweet or not sweet enough for the number of calories it contains, the body's normal metabolic response is disrupted.
The response explains the association between artificial sweeteners and diabetes discovered in earlier studies.
"A calorie is not a calorie," said senior author Dana Small, professor of psychiatry at Yale University School of Medicine.
The new study shows that sweetness helps to determine how calories are metabolized and signaled to the brain. When sweetness and calories are matched, the calories are properly metabolized, and this is registered by brain reward circuits.
However, when a "mismatch" occurs, the calories fail to trigger the body's metabolism, and the reward circuits in the brain fail to recognize that calories have been consumed. As a result, the person could be compelled to overeat.
"In other words, the assumption that more calories trigger greater metabolic and brain response is wrong," Small said. "Calories are only half of the equation; sweet taste perception is the other half."
Calories that aren't being metabolized were probably stored, she said, and may be an important clue into the mechanics behind metabolic syndrome, a condition that leads to heart disease and diabetes.
Small noted that it's not just soft drinks that contain mismatches, so do foods such as yogurt with low calorie sweeteners.
"Our bodies evolved to efficiently use the energy sources available in nature," Small said. "Our modern food environment is characterized by energy sources our bodies have never seen before."
The study was published in the journal Current Biology.
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