The concept of fizzy drinks making you fat isn’t all that radical. But what do we really mean by ‘fizzy’ (or carbonated) drinks, and why does drinking them lead us to gain the pounds in the first place?

Sodas like Coca-Cola and Mountain Dew, of course, are often stacked with sugar, with as much as eight teaspoons per can. But what about sugar-free sodas? Most of them are fizzy, and past research has shown that they can be linked with obesity too.

Heck, even carbonated water is technically a ‘fizzy’ drink …

Question is then, is it only the sugar in the soda that makes you fat, or is something else at play?


The answer might lie in a hormone called ghrelin. Sometimes called the ‘hunger hormone,’ ghrelin is formed in the digestive tract. Its main function is to regulate our appetite – when our stomach is empty, ghrelin is formed, which triggers the desire for more food.

Some recent research suggests a link between the carbon dioxide found in fizzy drinks, and the amount of ghrelin that gets produced in the gut.


Researchers at Birzeit University in the West Bank conducted a study with healthy adult males and lab rats – rats also produce ghrelin. It was later published in the Peer Reviewed Journal ‘Obesity Research and Clinical Practice.’

Four groups of male rats were given a standard diet, along with one of four differing drinks:

  • Tap water
  • Regular soda (degassed/flat)


  • Regular soda (fizzy)
  • Diet soda (fizzy)

After 6 months, the rats drinking the tap water and the uncarbonated soda weighed significantly less than the ones drinking fizzy soda. This included the sugar-free fizzy soda.

The ones drinking the fizzy beverages also had more fat in the liver. The conclusion was that ghrelin levels in those groups of rats were higher, and that they ate more food as a result.

The team also had twenty adult males aged between 18 and 30 drink one of the four drinks one hour after a light breakfast (hopefully from a different cup that the rats got …)

Blood samples were then taken to compare ghrelin levels. The experiment was repeated over a number of days so that each subject had tried all of the drinks.

For the subjects drinking fizzy soda, it was found that ghrelin levels were six times higher than the subjects drinking tap water, and three times higher than those on flat soda.

James Brown eating a Cheese Sandwich

The Hardest Working Nutritionist in Show Business

Some interesting results, but what about sparkling water? Surely drinking a naturally carbonated seltzer water or club soda couldn’t actually lead to weight gains?

Dr. James Brown from Aston University in the UK conducted a study broadly similar to the Birzeit team’s (and when the Godfather of Soul gets involved, you tend to sit up and take notice, ow!!)

Each day, twenty volunteers were given a cheese sandwich containing the exact same calorie count. They were then randomly assigned a drink. The list of drinks was the same as the Birzei University’s study, with the addition of sparkling water. Ten minutes after eating, the participant’s blood was sampled.

Over the course of the study, it was discovered that the combined ghrelin levels for the fizzy drinks were around 50% higher than the flat ones. And although it was by a smaller amount, there was still an increase even in the case of sparkling water.

The results also showed that the volunteers assigned fizzy drinks ate around 120 calories more on average, a statistically significant result.


Both studies certainly seem to point towards increased ghrelin levels and appetite in the participants drinking fizzy or carbonated drinks.

A possible explanation is that the carbon dioxide found in sparkling waters and soda stimulates the ghrelin receptors in the gut, causing us to feel hungry more quickly than otherwise.

Switching outright to still sugary drinks, however, probably isn’t the answer. It seems likely that the sugar found in these kinds of drinks, as well as with fizzy soda, is still far and away the biggest factor in any associated weight gain.

In reality, a person that drinks soda of any kind on a regular basis is likely to have a poorer diet, and probably lead a more sedentary lifestyle. It should also be noted that the sample groups in both experiments were small numbers of either people or rats. A longer study with more varied participants is probably needed for any more insights.

In the meantime, if you are concerned that even your favorite sparkling water might be making you crave those few more calories, you could always switch to still. Hey, if Mr. Dynamite himself is all for it, it can’t be THAT bad …

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