If you’re trying to lose weight, switching to diet pop might actually cause the opposite of the desired effect, new research suggests.

In a massive study spanning nearly 10 years and involving almost 500 participants, epidemiologists at the University of Texas’s School of Medicine in San Antonio found that drinking diet soda was associated with an increased waist circumference.

In fact, over the course of the study’s time span, people who consumed diet soft drinks experienced a 70 per cent increase in waist circumference compared to those who did not.

Moreover, those study participants who said they drank two or more cans of diet soda every day saw their waist circumferences increase as much as 500 per cent compared to those who avoided the sweet drinks.

The researchers point out that their findings don’t conclusively point to a definitive cause-and-effect relationship between drinking diet pop and weight gain — merely that those who drink diet sodas tend to see increased waist circumference over time.

“I’m pretty convinced that there’s enough evidence to suggest that using an alternative is wise,” said Helen Hazuda, professor and chief of clinical epidemiology in the University of Texas Health Science Center San Antonio School of Medicine.

Hazuda and her team began their research by assessing data from 474 Mexican Americans and European Americans in the San Antonio Longitudinal Study of Aging. They measured height, weight, waist circumference, and diet-soda intake. They then conducted three follow-up exams over the last decade. Even when adjustments are made for diabetes status, sex, ethnicity, years of education, physical-activity level, neighborhood-income level, age and smoking status, the results still stand.

“That gives us more confidence that maybe there’s something more causal going on,” Hazuda told the Star. “It is consistent with what some other large population-based studies have found.”

She did point to a number of factors that could have contributed to the weight gain, however. One is that some artificial sweeteners commonly found in diet soda are sweeter than sugar.

“Because they’re so sweet – as much as 180 times sweeter than sugar – they actually lead you to the point of craving even sweeter things, and these might be things that aren’t good for you,” she noted.

Hazuda also surmised that people may believe they can eat more because they are taking in fewer calories by drinking diet soda.

“They overcompensate, not realizing that they weren’t accomplishing much savings by drinking the diet-soda waters,” she said.

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Regardless of what caused the weight gain, Hazuda says if you want to lose weight, just avoid diet sodas altogether.

“Given the evidence we have right now, the healthiest choice would be not to drink the diet soda,” she said. “If you can drink water instead, that might be a very good alternative.”