Can Diet Sodas Cause Weight Gain?

San Diego, CA – The perception that diet sodas are a benign alternative to highly sweetened beverages might be dangerously wrong, according to the results of the San Antonio Longitudinal Study of Aging, which were reported here at the American Diabetes Association (ADA) 2011 Scientific Sessions [1].

Diet soft drinks have long been thought to be a healthier alternative to their sugary counterparts; however, past reports have linked increased incidence of weight gain, metabolic syndrome, and diabetes to the frequent intake of diet soda.

In the study presented, Sharon P Fowler (University of Texas Health Science Center at San Antonio) and colleagues examined the effect of the long-term consumption of diet sodas by a population of individuals 65 to 74 years of age (n=474).

At baseline, measures of height, weight, and waist circumference were recorded, as was diet-soft-drink intake. Three additional exams of the study subjects were conducted over an average follow-up of just over 3.5 years (the study was conducted over a nine-year period).

When the results of these observations were compared with those from subjects who did not drink diet soda, the differences were striking. Overall, consumers of diet soda drinks experienced a 70% greater increase in waist circumference than nonconsumers. Further, among elderly drinkers of two or more diet soda per day, mean increases in waist circumference were five times greater than those recorded for nonconsumers.

“These results suggest that—amid the national drive to reduce consumption of sugar-sweetened drinks—policies that promote the consumption of diet soft drinks may have unintended deleterious effects,” state the study investigators.

Dr. Jonny Comments: This is not the first time that diet soda consumption has been linked to weight gain and obesity. A 2005 study found that folks who consumed 1-2 cans a day of diet soda had a 54.5% greater chance of being overweight or obese. That same study found that for each can of diet soda consumed each day a person’s risk of becoming obese went up by 41%.

So what to make of this?

One theory is that calorie-free beverages that taste sweet fool the body and somehow upset the appetite control centers in the brain. Another is that the sweet taste may actually produce an insulin response in much the same way as Pavlov’s dogs became conditioned to salivate at the sound of a bell. (Insulin, as you know, is the “fat storage” hormone and rises dramatically when sugar is consumed.)

But a third interpretation is that these studies don’t mean anything. Folks who take this position point out that people who are already overweight tend to consume diet drinks, but that doesn’t mean the diet drinks made them overweight.

Truth is, we don’t know which- if any- of these hypotheses explains the facts, but the facts remain: For whatever reason, consumption of diet sodas increases your risk of gaining weight.

And since there’s basically nothing good in diet soda– which is made of chemicals, potentially dangerous artificial sweeteners, and a bunch of artificial coloring and flavoring–  it’s hard to find a good reason to keep on drinking them.




  1. Josh

    I believe that the aspartame in most diet drinks causes cravings and makes people eat more, or at least make bad or worse food choices. Also, some people think that just because they’re drinking a diet soda, they can eat anything and everything they want.

  2. Mary Nash Stoddard

    Thank you, Dr. Jonny for sharing this excellent article on Obesity and Diet Sweeteners. We’ve been saying this very thing since 1987, when we gave testimony at the Sen. Hearing on Aspartame Safety. Now, the world is listening and lives are being saved because of it. Please join us at our not-for-profit, Aspartame Consumer Safety Network and Pilot Hotline (1987-2011) and add your voice to ours – educating people around the world about the reported dangers of Aspartame/Neotame ingestion. Our friend, Robert Crayhon said: “Mary Nash Stoddard is a National Treasure.” on his WOR radio show. I’ve been trying hard to live up to his expectations and standards. Because of amazing mentors, like Robert, we are able to carry on our important work around the world today. Artificial Sweeteners are indeed making people fatter and worse. Help us save lives – one consumer at a time. Bless you — Mary Nash Stoddard/author Deadly Deception Story of Aspartame

  3. Rick Merr

    A couple of problems with this article. First the links referred to are observational studies which in and of themselves do not prove anything. They merely provide a starting point for a hypothesis that needs proper scientific testing. Single blind studies have found that at least sucralose does not increase appetite nor blood sugar which are the hypothesis generated by the above article.
    The second issue I have is the question of why anybody would want to drink a diet soda. I can think of many reasons but the point I would like to make is that the consumption of diet soda may not neccessarily be to lose weight, but to help you do the things that will cause you to lose weight. I myself have used an occasional diet soda with sucralose to ease the yearning of my sweet tooth and as an award or incentive to soldier on in the course of low-carb eating for weight loss. I’m talking one or two diet sodas a week.

  4. Erica

    Just food for thought, diet coke has always decreased my appetite. Some people are just different, I suppose. I stopped drinking diet coke after I was severely dehydrated from it and I realized when quitting how hungry I was without it. It had been acting as an appetite suppressant for me.