Do You Need To Stop Diet Drinks To Lose Weight?

In the United States, sweetened carbonated beverages account for about one-fourth of all fluid consumption, more than juice, more than coffee, more than tea, and more than milk. Only water is drunk more often than sweetened soft drinks, and some people don't drink water at all.

There's a Lot of Sugar in Regular Sodas

When soft drinks are sweetened with high-fructose corn syrup, cane sugar, or honey, it's a no-brainer that they contribute to weight gain. A 12-ounce (365 ml) can of regular Coca Cola, for example, contains 39 grams of sugar that pack 140 calories. The more frequently consumed 20-ounce (590 ml) bottle of Coca Cola contains 65 grams of sugar worth 240 calories. A one liter bottle of Coca Cola, which is a little larger than a 7-11 Big Gulp, contains 108 grams of sugar for 400 calories. And if you drink 2 or 3 or 4 Cokes or similarly sugary soft drinks every day, the wonder isn't that you don't gain a couple pounds (a kilo or so) every week.

Most of the time, however, our bodies already are getting enough glucose from other carbohydrate foods, and extra sugar has to be burned in the liver or stored or fat. Since the liver can only process about 10 grams (40 calories) worth of fructose at a time, most of the sugar from soda water becomes fat. But what if the beverage is sweetened with aspartame (Nutrasweet) or sucralose (Splenda)?

Diet Soda Drinkers Gain Weight Even Faster

In the 1990's and the first decade of the 2000's, researchers at the University of Texas Health Sciences Center in San Antonio followed 474 people aged 65 to 74 in the  San Antonio Longitudinal Study of Aging, or SALSA. The researchers took measurements of height, weight, waistline, and diet soda consumption when volunteers were enrolled in the study and about every 2-1/2 years thereafter. 

The results of this study are widely quoted as:

• Diet soda drinkers experienced 70% greater increase to waistline measurements than non-diet soda drinkers and
• People who drank two or more diet sodas per day had an average 500% greater increase to waistline measurements than those who didn't drink any diet sodas at all.

See Also: Are Diet Soft Drinks Really Healthy For You?

Actually, the results of the study were a bit more nuanced than that. Among people who had diabetes, drinking diet sodas did not increase belly fat. Among people who made an effort to get into shape by increasing the amount of exercise they go, drinking diet sodas did not increase belly fat. And among people who were already obese, that is, they had a BMI over 30, drinking diet sodas did not increase belly fat. Only people who were in the best shape suffered a detrimental effect--measured in terms of increased abdominal waistline--when they drank more diet soft drinks.

If You Already Drink Diet Sodas, You Probably Don't Need To Quit To Lose Weight

We aren't ready to say that Nutrasweet and Sucralose sweetened diet beverages are healthy. There are other issues with artificial sweeteners. The dangers of these sweeteners have been exaggerated in the media for decades, but that doesn't mean they are good for you.

Dr. John Peters of the Anschutz Health and Wellness Center, University of Colorado, in Aurora, and his colleagues conducted a 12-week experiment in which 308 dieters in Colorado and Pennsylvania were enrolled in a diet education program and asked either to drink at least 24 oz (720 ml) of water per day and no artificially sweetened beverages, or to drink at least 24 oz of artificially sweetened soft drinks. The average age of the volunteers was 48, unlike the study in San Antonio, this clinical trial included a significant number (28%) of African-Americans, everyone in the program was diagnosed as obese (average BMI of 34) at the beginning of the program. Participants chosen for the study were not getting any exercise at the beginning of the diet.

None of the dieters reported problems drinking enough water or enough diet soda. The dieters also increased their physical activity to 90 minutes a week.

At the end of the 12 weeks, the dieters who had been asked to be sure to drink diet soda lost, on average, 5.95 kg (a little over 13 pounds).  Dieters who had been asked to drink water everyday lost on average 4.09 kg (a little under 9 pounds). The dieters who had been drinking diet sodas reported fewer problems sticking to their diet plans than the dieters who drank water. Drinking artificially sweetened beverages reduced hunger--not a lot, but enough to make a difference.

The researchers in this study don't know exactly why drinking diet beverages increased rather than decreased weight loss in these carefully selected dieters. They don't know whether people who drank Nutrasweet-sweetened carbonated beverages ate less or burned more fat, although the indications from participant reports is that drinking diet soft drinks helped them to eat less. And the fact that the study was funded by the American Beverage Association may also have some bearing on its results.

See Also: Drinking Diet Soda Is Not A Solution For Weight Loss

That is, they don't make the situation worse. Researchers counsel against starting diet soft drinks to lose weight if you don't drink them already, but it also appears it isn't helpful to give them up (you'll just be looking for something sweet to eat in their place) and it isn't helpful to drink more water. There may be many other reasons not to consume Nutrasweet, but successful weight loss dieting is not among them. Eat less, and at least don't drink more diet soda than you do now.