The findings come from eight years of data collected by Sharon P. Fowler, MPH, and colleagues at the University of Texas Health Science Center, San Antonio. Fowler reported the data at this week's annual meeting of the American Diabetes Association in San Diego.
"What didn't surprise us was that total soft drink use was linked to overweight and obesity," Fowler tells WebMD. "What was surprising was when we looked at people only drinking diet soft drinks, their risk of obesity was even higher."
In fact, when the researchers took a closer look at their data, they found that nearly all the obesity risk from soft drinks came from diet sodas.
"There was a 41 percent increase in risk of being overweight for every can or bottle of diet soft drink a person consumes each day," Fowler says.
More Diet Drinks, More Weight Gain
Fowler's team looked at seven to eight years of data on 1,550 Mexican-American and non-Hispanic white Americans aged 25 to 64. Of the 622 study participants who were of normal weight at the beginning of the study, about a third became overweight or obese.
For regular soft-drink drinkers, the risk of becoming overweight or obese was:
- 26 percent for up to 1/2 can each day
- 30.4 percent for 1/2 to one can each day
- 32.8 percent for 1 to 2 cans each day
- 47.2 percent for more than 2 cans each day.
- 36.5 percent for up to 1/2 can each day
- 37.5 percent for 1/2 to one can each day
- 54.5 percent for 1 to 2 cans each day
- 57.1 percent for more than 2 cans each day.