Diet drinks may encourage long term weight gain

Back in May we wrote about a study that seemed to show that drinking beverages sweetened with calorie-free sweeteners would actually help you lose weight. The problem, however, is that the study was funded by The American Beverage Association and two of the researchers involved had been paid consultants for Coca-Cola, who (surprise, surprise) is one of the three largest members of The American Beverage Association.

Other, more reputable research into the effects of drinking these types of beverages is rather more mixed, with some research suggesting that those drinking diet drinks instead of sugar-sweetened beverages were more likely to become overweight or obese over time. Research in rats has suggested that drinking beverages sweetened with calorie-free sweeteners may affect the individual's ability to judge the number of calories actually consumed.

A team at Texas Christian University theorized that the effect of these beverages sweetened with non-caloric sweeteners (NCS) might be far more subtle and long term than had previously been thought (Appetite 2014;83:82-88). They designed a set of three experiments to assess people's psychological and behavioral responses to consuming beverages sweetened with NCS.

At the start of all three of the studies the participants (all students at the university) were randomly given one of three drinks in a red plastic Solo(r) cup: regular Sprite; Sprite Zero (sweetened with a NCS); or an unsweetened sparkling water flavored with natural lemon and lime flavorings.

For the first study the participants consumed their beverage, then were shown different words flashed on the computer screen. They were directed to indicate as quickly as they could whether the word was real word or a non-word by pressing certain keys on the computer keyboard. Three types of words were presented: the name of a high-calorie food (burger, cookie, pizza), the name of a low-calorie food (celery, apple, radish), or a non-word (ebusun, ganeap, tigne).

The second study directed the students to respond to a series of questions about the packaging of three items - a bag of M&M's, a bottle of plain water, and a pack of sugar-free gum - after consuming their beverage. After completing the questionnaire, the students were told that they could choose one of the products to take home with them.

For the last study, the panelists consumed their assigned beverage and then were directed to taste as many cookies as they wished from a standardized amount of mini Oreos. Afterward they responded to a survey about their impressions of the cookies' taste and how satisfied they felt after consuming them.

The results are quite interesting. The first study showed that compared to those who had drunk the flavored water or the sugar-sweetened beverage, those who had drunk the calorie-free Sprite responded most quickly when the high-calorie words were flashed on the screen, suggesting that the brain was primed to respond to high-calorie foods. Response time was not significantly different for the low-calorie or nonsense words. Further, those who drank the sugar-sweetened beverage or the mineral water had no significant differences in their response time regardless of the type of word.

Those who drank the NCS beverage were twice as likely as those drinking the sugar-sweetened beverage or the water to decide to take home the M&M's, in the second study, and in the third, they were least satisfied with the cookies they had eaten, although they liked the taste and ate about as many of the cookies as either of the other two groups.

What this means for you

These are small effects that could lead to long term weight gain: being primed to react to higher-calorie foods, making less-healthy choices, and being less satisfied with what you eat along with your diet drink. While this is a small study and bears further research, it's another indication that your best bet is still water, coffee (regular or decaf), or tea.

First posted: September 17, 2014