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How can drinking diet soda lead to weight gain?

Dr. Michael Roizen, MD
Internal Medicine
Zero calories, it turns out, don't have zero impact when it comes to weight. A recent study shows that people who drank diet sodas had a 70% greater increase in waist circumference over a few years than people who didn't drink them. Any excess fat is bad, but belly fat is the worst. It's linked to diabetes, heart disease and some cancers.

How can something that's basically chemicals and coloring be fattening? First, sweet diet soda fuels your desire for other sweets. Second, it has a "health halo" effect. You view choosing a "diet" drink as virtuous (all those calories saved!). So it feels like you can afford to reward that virtue with a hot fudge sundae or a fast-food burger that's bigger than Texas.

It's not the diet soda that's fattening. It's the sense that drinking it somehow erases the calories of what you eat with it. A diet drink now and then won't make you fat -- as long as you're not using it to wash down a fried calorie bomb from the drive-through.
Marjorie Nolan Cohn
Nutrition & Dietetics

Diet soda can affect weight on both a physical level and on a psychological level. On a physical level, diet sodas are full of artificial flavors and sweeteners. Even though diet soda has no calories, the artificial flavor and sweetness trigger the digestive process via your taste buds. And your intestine starts to secrete digestive juice in preparation for digestion. Problem is there is nothing to digest. This in turn, leaves your cells hungry for the sweetness that they thought they were getting but never did, sugar cravings ensue. Many people ultimately eat more later in the day. On a psychological level, when someone drinks diet soda knowing it has less calories it creates an attitude that they have extra calories to eat other foods. Often this leads to more eating. A good example of this phenomenon is when someone orders a diet coke with his or her double bacon cheeseburger and large fry. At that point the soda is minor compared to the burger and fries.

Christie Parsons, RD
Nutrition & Dietetics
Drinking diet soda does not have any calories associated with it, so drinking diet soda in and of itself will not directly cause weight gain. With that said, if you think you are gaining weight, look closely at what else you are eating. If you are thinking “because I drank that diet soda, I can have……” and then choose to eat or drink foods/beverages with high calories, you may have to teach yourself to rethink. In a nutshell, for the most part, when someone consumes more calories than they use, they will gain weight. Calories are your body’s energy. When you have too many, your body will store them for later. Any time you have more than you need at that moment, you will store them as body fat, aka weight. If you are unsure where the extra calories are coming in, make the decision to write down EVERYTHING you consume for 3 days. Include sauces, dressings, beverages, etc. This will give you a good idea of what you are eating.  We often forget the cookie here or the chips there and wonder why our pants are a little tighter. Once you get a good idea of what is going on, make 1 change at a time. One week, you could decide to only drink calorie-free beverages. The next week, you could choose to replace one snack per day with a fresh fruit or vegetable snack.
Dr. Mike Dow, PsyD
Addiction Medicine

Believe it or not, drinking diet soda can actually lead to weight gain because it confuses your metabolism and sense of taste. Watch as psychotherapist Mike Dow, PsyD, discusses why drinking diet soda may have the opposite effect of what you want.


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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.