Research overwhelmingly suggests that consumption of sugar sweetened beverages including pop and juice is linked with obesity and type-2 diabetes. Specifically, overconsumption of sugar can lead to excessive weight gain and an increased risk of type-2 diabetes. Many people turn to diet drinks sweetened with artificial sweeteners to cut their consumption of sugar while still enjoying a sweet drink. These drinks provide minimal calories but still give a sweet taste. Most nutritional studies to date have focused on the sugar or sugar-alternative content in drinks to determine risk for obesity and type-2 diabetes, however there is another element that is present in all soft-drinks; carbonation. Carbon dioxide is added to soft-drinks under pressure to make acidic and sharpen the flavour, and to help preserve them for a longer shelf life. A team of researchers from Palestine has decided to investigate whether the carbonation of soft drinks plays any role in the obesity and type-2 diabetes epidemic currently affecting our society.
Using male rats, the team of researchers fed them a normal chow diet but replaced their water with either a sugar carbonated beverage (regular pop), diet carbonated beverage (diet pop), or pop that had been degassed (no carbonation). They monitored their weight and food consumption for 100 days and found that the mice who drank carbonated beverages, regardless of if they had sugar or not, ate more food and weighed about 15% more than those who drank water or drank the degassed pop. Additionally, the mice who drank carbonated beverages (diet or regular) had more of the hunger hormone ghrelin circulating in their blood. Ghrelin is normally secreted when your stomach is empty to signal your brain to eat, when your stomach is full ghrelin secretion is turned off. If the scientists took the stomachs out of the rats and put carbonated drinks on them, they began to secrete ghrelin. This was not the case if they used water or the degassed drinks proving that the carbonation in the stomach was responsible for causing the secretion of ghrelin. There was also a significant increase in the amount of fat deposited in the livers of rats who drank carbonated beverages compared to those who had water or non-carbonated drinks.
To understand how these results may translate to a human population, the researchers gave 20 healthy males (18-23 years old) water, carbonated pop, carbonated diet-pop, carbonated water, or degassed pop on different days (always at 9am). One-hour after breakfast (same meal for all groups), the students drank their assigned drink and the researchers measured ghrelin levels in their blood. As they suspected, there was an increase in ghrelin secretion in the people who drank carbonated pop or diet pop compared to water and to degassed (non-carbonated) pop. To their surprise, the people who drank carbonated water (no sugar) also had an increase in ghrelin to a similar level as those who had carbonated pop. This finding supported their hypothesis that carbonation in a drink causes the body to secrete ghrelin, making people think they are hungry even if they are not. This then causes them to over consume food and, in conjunction with the sugar intake, causes them to gain weight. The teams working theory is that the carbonation in the beverages puts pressure on the stomach wall that causes the secretion of ghrelin.
There are a few limitations to keep in mind with this study. First, while they did measure ghrelin levels in humans, the majority of the results come from rat models and so still need to be validated in other models and in humans. Second, only males were tested (in both rat and human studies). We don’t yet know if the same result holds true for females. Finally, the exact mechanism by which carbonation induces ghrelin release and excessive food consumption is unknown. While more work still needs to be done, this study does suggest that over consumption of carbonated beverages whether they contain sugar or not contributes to overeating, weight gain, and perhaps type-2 diabetes.
Image Credit: Flickr Aislinn Ritchie