How Might Carbonation Contribute to Obesity?

Carbonation makes drinks seem less sweet than they really are, and could increase consumption of sugar and food, neuroscientists report in the September issue of Gastroenterology. It might be therefore be best for weight-loss plans to avoid carbonated beverages.

Addition of carbon dioxide (CO₂) to water (carbonation) makes it effervescent and pleasant. Consumption of sweetened carbonated drinks has increased exponentially, and been associated with the growing rates of obesity and metabolic diseases.

Surprisingly, the consumption of diet sodas, which have few or no calories, has also been linked with obesity and poor health.

Francesco Di Salle et al. investigated the effects of CO₂ on perception of sweetness from sucrose (sugar) and artificial sweeteners (aspartame-acesulfame, a common combination used in diet beverages), monitoring changes in regional brain activity with functional magnetic resonance imaging.

The presence of carbonation produced an overall decrease in the neural processing of sweetness-related signals, especially from sucrose.

Di Salle et al. observed that CO₂ reduced activity in the gustatory regions of the brain, such as the anterior-insula, orbitofrontal cortex, and posterior pons in response to carbonation, independently of what sweetener the drink contained. However, the effect of carbonation on sucrose was stronger than the effect on artificial sweetener.

In behavioral studies, the authors also found that CO₂ reduced sweetness perception and the differentiation between natural and artificial sweeteners. The ability of CO₂ to reduce the perception of sweetness from sucrose could increase sugar intake among soda drinkers. But what about in drinkers of diet sodas?

In an editorial that accompanies the article, Catia Sternini says that tricking the brain about the type of sweet could be advantageous to weight loss because it facilitates the consumption of low-calorie drinks—their taste is perceived as pleasant as the sugary, calorie-laden drink. However, the downside is that this perception could alter energy homeostasis and balance to stimulate sugar consumption. This could explain the prevalence of eating disorders, metabolic diseases, and obesity among diet soda drinkers.

Di Salle et al. add that perception of CO₂ is accompanied trigeminal somatosensory stimulation that leads to multisensory convergence of perceptual inputs, which could indicate to the human brain a nutrient-rich feeding environment. Carbonation might therefore make people feel like eating.

According to Sternini, the sense of taste in the mouth, along with the sight and the smell of food and drink, initiates physiologic reflexes beyond the oral cavity, such as the secretion of digestive enzymes, hormones, and other signaling molecules from the gastrointestinal tract and its associated glands. These prepare the gut to digest and absorb nutrients, and could increase eating.

Future studies to analyze the effects of carbonation on the brain as well as the gastrointestinal lumen.

Read the article online.
Di Salle F, Cantone E, Savarese MF et al. Effect of carbonation on brain processing of sweet stimuli in humans. Gastroenterology 2013;145:537–539.e3

Read the accompanying editorial.
Sternini C. In search of a role for carbonation: is this a good or bad taste?Gastroenterology 2013;145:500–503.