Do Diet Sodas Cause Weight Gain?


Diet sodas are in the news again. You’ve probably seen the headlines questioning whether diet sodas actually help you lose weight. In fact many of the headlines imply the diet sodas will cause you to gain weight. Two of the more sensational headlines I came across said “Think diet sodas help you lose weight? Not so, Purdue study finds”, and “Can diet sodas actually cause more weight gain than regular sodas?”

Let me start with those last two headlines. In the first place, there is no good evidence that diet sodas will cause you to gain more weight than regular sodas.  Secondly, the Purdue publication (Swithers, Trends in Endocrin. Metab., wasn’t really a study, it was an opinion piece. That simply means that it was a review where the references were selected on the basis of the author’s opinion.  That’s OK if you clearly label it as an opinion piece, which Dr. Swithers did.  And the evidence that Dr. Swithers cited was pretty impressive. There were studies showing that consumption of diet sodas was associated with weight gain, increased risk of pre-diabetes and type II diabetes, increased risk of high blood pressure, and increased risk of cardiovascular disease. However, one limitation of all of those studies is that they were looking at associations, not cause-and-effect. So, for example, it’s not clear whether the people in those studies gained weight because they were consuming diet sodas or consumed diet sodas because they were gaining weight.  There have been very few intervention studies, namely studies in which one group of subjects were told to drink only diet sodas and the other group only regular sodas. Unfortunately, in those studies the total caloric intake of the diet soda group was also restricted. So while the diet soda group did lose weight, it’s not clear whether that weight loss was due to the diet sodas or the overall caloric restriction of the diet.

So what is the average consumer to think? On the one hand, dietitians and health professionals are telling you to drink diet sodas if you want to lose weight. On the other hand, you keep seeing these headlines saying the diet sodas may not help you lose weight or may even cause you to gain weight.

Of all the recent blogs and online articles on the topic, the only one I actually recommend reading is from WebMD

WebMD often adheres to the AMA line, but I found this to be a very balanced analysis of the science behind the question of whether diet sodas help or hinder weight loss.

I think the useful perspective from that article is that it’s not the diet sodas themselves that cause weight gain. It’s what we eat with the diet sodas that cause the weight gain. Here are a couple of quotes I found particularly enlightening.

Dr. Barry Popkin, a colleague from the University of North Carolina, calls it the “Big Mac and Diet Coke”
mentality. He says: “Especially in America, we have a lot of people who eat high-fat, high-sugar diets, but also drink diet sodas.”

Why is that? Dr. David Katz from Yale University has research suggesting that artificial sweeteners may
condition people to want to eat more sweet foods. He says: “Our taste buds don’t really differentiate between sweet in sugar and sweet from, say, aspartame. The evidence that this sweet taste is addictive is pretty clear. What I have seen in my patients is that those who drink diet soda are more vulnerable to processed foods with added sugars.”

The Bottom Line

– Once again there is no magic bullet. Diet sodas aren’t going to help you lose weight unless you carefully control the calories in everything else you eat. And, diet sodas may just cause you to crave the very foods that are worst for your waistline.

– There is no substitute for a healthy, calorie controlled diet; exercise; and lifestyle change if you want to lose weight and keep it off.

To Your Health!
Dr. Stephen G Chaney

Author: Dr. Steve Chaney, Professor of Nutrition & Biochemistry, UNC

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