Ask the Doctors: Study linked drinking carbonated water, weight gain

Dear Doctors: As part of a reducing diet, we like to drink plain carbonated water. There’s no sugar in it, no additives and no sweeteners. But apparently there is a new study that says carbonated water leads to weight gain. Why? Should we give it up?

Answer: Carbonated water gets its bubbles by being infused with carbon dioxide gas under pressure. With no added sugars and no calories, it has become a mainstay of American life.

But a study published several years ago in the journal Obesity Research and Clinical Practice linked drinking carbonated water to weight gain. It didn’t blame the beverages directly, instead suggesting that the carbon dioxide that gives fizzy water its effervescence has an effect on body chemistry that can lead to overeating.

The scientists looked at how plain and artificially sweetened carbonated water affected rats over the course of a year and found that those that drank either type of sparkling water gained more weight than those that drank only plain water or carbonated water that had been degassed.

The carbonated water was causing the rats to secrete increased levels of the hormone ghrelin. Among ghrelin’s many functions is signaling the body it’s time to eat. When the stomach is empty, concentrations of this “hunger hormone” increase. This leads to the sensations we interpret as hunger.

The researchers also looked at the effects of sparkling water in humans. They had 20 men drink carbonated or plain water, and the results matched those of the rodent study. The men who drank either unsweetened or artificially sweetened carbonated water had triple the blood levels of ghrelin as those who drank plain water or degassed sparkling water. The study rotated the four beverages among all of the participants, so, by the end of the study, each man had partaken of each beverage. They concluded that the presence of carbon dioxide led to an increase in ghrelin production.

These findings raise questions about the role of fizzy water in weight management.

But a single study with a small pool of all-male human volunteers can’t be considered conclusive. While ghrelin is known to stimulate appetite, its role in overeating and obesity is a subject of debate.

Rather than take the research as established fact, you might try an experiment of your own. Compare hunger levels on days you drink carbonated water with days you don’t. Based on your results, you can choose to cut back — or cut out — your intake.

Dr. Eve Glazier and Dr. Elizabeth Ko are internists at UCLA Health.