Is Diet Soda Making You Gain Weight?

Diet soda sounds like an easy way to cut calories, but new research shows it may not be good for weight loss. Learn why diet soda may actually cause you to gain weight, among other problems.

By Chris Iliades, MD 

Medically reviewed by Pat F. Bass III, MD, MPH

If you feel better about having a burger and fries for lunch because you ordered a diet soda, you shouldn't. Studies show that diet soda may not be any better for you than regular soda. In fact, it may even be worse.

Close to 60 percent of Americans drink diet soda on a regular basis. Many of them believe diet soda helps them with weight loss, but there is mounting evidence that diet soda may actually cause you to gain weight.

Diet Soda and Weight Loss: What Research Revealed

"Recent literature suggests that those who drink diet soda weigh more than those who don't. That shouldn't surprise anyone. Does diet soda cause weight gain? I think that is the wrong question. I don't think people should drink diet soda, whether they have weight problems or not," says Darwin Deen, MD, senior attending physician at Montefiore Medical Center's Department of Family and Social Medicine in the Bronx, New York.

Of top concern, drinking diet soda has been linked to developing metabolic syndrome. Metabolic syndrome is a group of conditions that include expanding waist size, increased blood pressure, elevated triglycerides, lower levels of good cholesterol, and high fasting blood sugar levels. Having three or more of these findings increases your risk of diabetes and heart disease. Here are some other research findings you should know about diet soda:

• According to the San Antonio Heart Study, the more diet sodas you drink, the greater the chance that you will be overweight or obese. For each diet soda you drink there is a 65 percent increase in your risk of becoming overweight.
• According to the Framingham Heart Study, if you drink diet soda you are at risk for weight gain andmetabolic syndrome.
• According to research done at Purdue University, rats that were fed artificial sweeteners gained more weight than rats fed normal sugar.
• Findings from the Atherosclerosis Risk in Communities Study sponsored by the National Heart, Lung, and Blood Institute, show that meat, fried food, and diet soda are all significantly associated with metabolic syndrome.

Diet Soda and Weight Loss: Why the Weight Gain?

Although researchers can't say for sure why diet soda sets the stage for weight gain, there are several possible reasons. "I discourage my patients from drinking diet sodas because while they have no calories, they are created to simulate the sweetness of a regular soda. This leaves the drinker’s taste buds completely overwhelmed. For an example of this, take a sip of water and then bite into your favorite fruit. Then try the same experiment with diet soda. Note that the real food tastes flat after drinking soda," explains Dr. Deen. The distortion of taste may cause the diet soda drinker to seek higher calorie foods.

Another possibility is that people just eat more because they think they are saving calories from drinking a diet soda. A direct link between artificial sweeteners and a craving for high-calorie foods may exist. There is also the possibility that the link is related to unknown factors involving diet, exercise, or other personal characteristics.

Diet Soda and Weight Loss: Caffeine’s Role

Although diet soda has fewer calories than regular soda, the caffeine content may be greater. According to the Center for Science in the Public Interest, a 12-ounce regular Coke contains 35 milligrams of caffeine and a Diet Coke contains 47 mg. At low levels, caffeine can stimulate energy, make you more alert, and may be beneficial for weight loss. In higher amounts it can cause nervousness, increased heart rate, and difficulty concentrating. You may also get withdrawal symptoms such as headache, irritability, or depression if you stop taking caffeine suddenly.

"Although caffeine can be helpful for weight loss, I recommend getting your caffeine from iced coffee. If you need to add sugar, add as little as possible for taste," says Deen. "I advise my patients to drink water. For a healthy alternative to diet soda, try adding one-third cup of fruit juice to seltzer water for a low-calorie and not-too-sweet beverage.”

Although the exact relationship of diet soda to weight gain and metabolic syndrome is not clear, it is obvious that diet soda should not be considered a “healthy” alternative to regular soda. When you choose to drink any soda, you are choosing to drink a beverage that is just not as healthy for you as milk, juice, or water.