Recent studies and experiments suggest that there could be another reason why carbonated drinks are associated with weight gain and obesity

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Fizzy drinks have been public health enemy number one over the last few years in particular, with Cancer Research UK  arguing that a 20 per cent sugar tax could prevent 3.7 million cases of obesity over the coming decade, while Jamie Oliver lobbied the government on the matter - it’s since been announced that a tax on sugary soft drinks will be introduced in Britain as of April this year. Intriguing research and an experiment carried out by  Dr Michael Mosley  appears to demonstrate, however, that the link between fizzy drinks and weight gain could be more complex than simply sky high levels of sugar, as fizzy water also appears to spike our appetite.

Dr Mosley was impelled to look into other reasons why carbonated drinks seem to propel weight gain after a study was published last year showing that rats who drank fizzy drinks, whether regular or diet, ate more and gained more weight over a six month period than rats who drank flat drinks or water.  Scientists from Birzeit University in Palestine  then followed up their research by testing their theory on twenty male participants, who showed a higher increase in the hormone ghrelin (which regulates our appetite) after drinking both sugary and diet fizzy drinks compared to flat drinks or water, in the same manner as the rats. Researchers interpreted that carbonation, as well as sugar, could heighten the risk of weight gain, obesity and fatty liver disease, owing to this surge in ghrelin release.

Dr Mosley put this to the “cheese sandwich test” in a recent episode of the BBC’s  Trust Me I’m A Doctor , asking healthy human volunteers to eat identical cheese sandwiches after a ten hour fasting period, followed up an hour later by either a glass of a sugary fizzy drink, a glass of the same drink, but flat, a glass of fizzy water or a glass of flat water. Blood samples were taken ten minutes later to measure ghrelin levels, then volunteers kept a food diary following the experiment to note down what (and how much) they ate afterwards. The same participants repeated the experiment over the course of a few weeks, with different drinks each time. Results showed that ghrelin levels were a whopping 50 per cent higher in the fizzy drinks group, but that’s not all…

Fizzy sugary drinks appeared to cause a notable increase in hunger an hour after consumption compared to the flat variety of the same drink, but even fizzy water triggered a rise in ghrelin levels. Overall, participants consumed 120 calories more on average after drinking fizzy drinks than they did flat drinks. The reasons for this are still not clear, but Dr James Brown, who helped Dr Mosley with the experiment, has a few theories:

“One is that after drinking a carbonated drink, carbon dioxide is released in your stomach. There are chemical receptors in the stomach which detect carbon dioxide and cause the cells at the top of the stomach to release ghrelin and it makes you feel hungry.

Another possibility is it is a mechanical thing. The stomach bloats and stretches a little bit from that extra gas and again that stimulates cells to release ghrelin. Those are the best two possibilities in terms of mechanism.”

This isn’t a licence to go chugging flat Coke- one can contains seven teaspoons of sugar, which is clearly bad news for teeth, weight gain and general health, but the apparent link between carbonation and ghrelin release provides an interesting avenue for further research. Finally, don’t panic that you’re damaging your health if you’re a San Pellegrino fan (the day that we demonise water is a sad one). If you do feel ravenous afterwards thought, you could have a clue as to why…

15 reasons to avoid sugary fizzy drinks

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