TL;DR

Zero calories doesn’t mean zero consequences. Long-term studies show people who drink diet soda regularly tend to gain more weight and belly fat than those who don’t. Artificial sweeteners may increase hunger, disrupt fullness signals, and change how the brain responds to sweetness. Bottom line: drinking diet soda to lose weight can backfire over time.

Does Diet Soda Do Any Good?

Dieters, in their quest to consume fewer calories, often opt to drink diet soda instead of sodas with sugar in them. This may not be a very good strategy for losing weight. While some (not all) short-term studies report slight weight loss with their use, long term use is problematic. A one-year study conducted by the American Cancer Society found that their use produced weight gain [2].

Long-Term Diet Soda Consmption and Weight Gain

The San Antonio Heart Study examined 3,682 adults over a seven- to eight-year period in the 1980s found that on average, people who drank a lot of diet drinks gained about twice as much body weight as those who drank very little [2]. Newer studies support these findings [3-6]. Consumption of them during pregnancy can even affect the weight of the newborn [5].

Diet Soda and the Microbiome

We choose diet drinks believing they help with sugar tolerance. That may not be the case. Studies show a connection between aspartame consumption and weight gain [7,9]. In one animal study, mice fed food that was high in aspartame an artificial sweetener (sold under the brand name Nutrasweet) actually had higher blood sugar levels than mice not fed aspartame [7]. One of the researchers, postulated that aspartame could trigger an increase in appetite, but do nothing to satisfy it. It can interfere with the body’s ability to feel full and can cause overeating.

Do Diet Sodas “Fool the Brain”?

Taste buds may perceive that the drink is sweet, but the brain knows the difference. One study found that women could not tell the difference between sugar and Splenda in taste tests. When the brain was viewed with functional MRI scans, it was determined that the brain’s reward center responded more completely to sugar than to artificial sweetener. “Your senses tell you there’s something sweet that you’re tasting, but your brain tells you, ‘actually, it’s not as much of a reward as I expected,’” said Dr. Martin P. Paulus, a professor of psychiatry at the University of California San Diego and one of the authors of the study [8].

  1. Artificial sweetener use and one-year weight change among women. Prev Med. 1986;15:195–202.
  2. Fueling the obesity epidemic? Artificially sweetened beverage use and long-term weight gain. Obesity (Silver Spring, Md.) 2008;16:1894–1900. 
  3. Plos One November 23, 2016 Chronic Low-Calorie Sweetener Use and Risk of Abdominal Obesity among Older Adults: A Cohort Study
  4. J Am Geriatr Soc. 2015 Apr;63(4):708-15. Diet soda intake is associated with long-term increases in waist circumference in a biethnic cohort of older adults: the San Antonio Longitudinal Study of Aging
  5. JAMA Pediatr Published Online: July 2016 2016;170;(7):662-670. Association Between Artificially Sweetened Beverage Consumption During Pregnancy and Infant Body Mass Index
  6. Beverage consumption patterns in elementary school aged children across a two-year period. J Am Coll Nutr. 2005;24:93–98.
  7. Nature 2014 Oct 9;514(7521):181-6. Artificial sweeteners induce glucose intolerance by altering the gut microbiota
  8. NeuroImage Volume 39, Issue 4, 15 February 2008, Pages 1559-1569 Sucrose activates human taste pathways differently from artificial sweetener
  9. . 2025 Mar 30;105(5):2737-2747. A critical review on effects of artificial sweeteners on gut microbiota and gastrointestinal health