New psychological research provides clues as to why consuming such drinks can actually lead to weight gain.

In recent decades, artificially sweetened beverages have become an increasingly popular alternative to sugary sodas. At the same time, America’s obesity rate has risen to epidemic levels.

Odd coincidence? Perhaps not: Considerable research has found consuming these “diet” drinks results in weight gain over the long run. At first glance, this seems preposterous, since you’re substituting a high-calorie product with a no-calorie one.

But in a newly published paper, a research team led by Texas Christian University psychologist Sarah Hill finds drinking these non-sugar beverages can “influence psychological processes in ways that—over time—may increase calorie intake.”

In a series of experiments, Hill and her colleagues discovered artificially sweetened beverages impacts our subsequent reactions to sweet food in ways that are distinctly different from either sugar-sweetened or non-sweetened drinks. Their research, published in the journal Appetite, suggests these products may activate a craving without satisfying it, thus increasing our vulnerability to the next high-calorie treat that crosses our path.

A body that believes it is getting an energy boost (as the sweet taste of the soda implies) and then does not may react by going into WTF mode (Where’s the Fructose?).

In one experiment, 115 undergraduates who had been fasting for at least eight hours drank one of three 12-ounce beverages (served in an unmarked cup): Sprite (sugar-sweetened); Sprite Zero (artificially sweetened); or lemon-lime flavored sparkling mineral water (unsweetened).

Afterwards, they took a test in which they were presented with 28 strings of letters, each of which flashed on a computer screen for 250 milliseconds. Participants were instructed to push one key if the string was an actual word, and another if it was not.

The researchers noted how long it took for them to notice the embedded words, which included seven high-calorie foods (including burger, cookie, and pizza), and seven low-calorie foods (such as celery and carrots).

“Participants who consumed the non-caloric sweetened beverage responded more quickly to the names of high-calorie food items compared to those who consumed either the sugar-sweetened or unsweetened drink,” Hill and her colleagues report. Interestingly, no differences were found between those who drank the sugary soda and the mineral water.

Another experiment featured 115 undergraduates who similarly drank one of the three beverages. Each then opened a box containing a bottle of natural spring water, a pack of Trident sugar-free gum, and a bag of M&Ms. After evaluating each product’s logo and packaging (to distract them from the actual intent of the study), they were told “they could choose one of the products to take with them when leaving.”

The results were striking: Those who drank the artificially sweetened drink were 2.93 times more likely to take the candy than those who had consumed either the sugary soda or the mineral water.

The researchers could not draw a definitive conclusion as to why drinking the diet soda had this effect, but they suspect it is based on “the decoupling of sweetness with energy availability.”

To put it simply: A body that believes it is getting an energy boost (as the sweet taste of the soda implies) and then does not may react by going into WTF mode (Where’s the Fructose?). This translates to cravings for the next high-calorie option that crosses our path.

While this study isn’t definitive, it does add to the evidence that artificial sweeteners may do more harm than good. Sure, they help us avoid calories in the short run. But in the end, we have to pay the Tab.