“Fizzy water could cause obesity by encouraging you to eat more,” The Daily Telegraph reports.
Researchers aimed to see whether it could be the carbonation in soft drinks – rather than the sugar – that explains the link between soft drinks and obesity.
Overall, they found rats that drank diet or regular fizzy drinks ate more and gained more weight over six months than rats that drank flat soda or water. The weight gain was associated with increased production of the appetite hormone ghrelin, which is produced by both rodents and humans.
The researchers then looked at the effects of carbonated drinks in 20 young men and found they also had higher blood ghrelin levels after drinking fizzy drinks than after flat soda or water.
But we can’t say from the results of this study alone that carbonation or ghrelin production is the full answer to the link between soft drink consumption and obesity.
It is likely that obesity is caused by multiple environmental, social and lifestyle factors, rather than carbonation on its own.
People who consume lots of fizzy drinks may also be more likely to have a less healthy diet and to be doing less exercise. The safest and cheapest bet for refreshment is plain old tap water.
Where did the story come from?
The study was carried out by researchers from Birzeit University in Palestine and was funded by grants from the same institution.
It was published in the peer-reviewed journal Obesity Research and Clinical Practice.
The coverage of the study in the UK media was accurate.
What kind of research was this?
This animal research aimed to see whether having fizzy drinks could contribute to weight gain.
The authors state that arguably there are many causes of obesity, including environmental, social and genetic factors. They say numerous studies have observed links between obesity and soft drink consumption, mostly believed to be due to the sugar content in these drinks.
But there’s another element to both sugar sweetened and diet fizzy drinks: carbon dioxide. This study aimed to look at the effects of carbonation.
Animal research is a useful step to see how biological processes may work in humans, as we share many similarities.
That said, we aren’t identical to rodents, so any findings would always need to be validated in human trials. Preliminary attempts at validation were made in this study. There are still likely to be many other issues involved with dietary intake and weight gain.
What did the research involve?
The study involved groups of male rats who were all fed a standard diet, but given one of four different drinks:
- tap water
- regular degassed (flat)
- soda regular carbonated soda
- diet carbonated soda
The researchers assessed food consumption, weighed the rats, and analysed blood sugar and cholesterol after six months on the diet.
They also looked at blood levels of the hormone ghrelin, which is released from the digestive system in response to hunger.
After death, the rats’ stomachs were also examined to see how much ghrelin had been produced and their liver was examined for fatty deposits.
In a second part of the study, 20 healthy human male students aged 18-23 were given a light breakfast followed one hour later by each of the four drinks.
The students repeated this experiment on different days so they were all trying the same drinks. They then had blood samples taken to measure ghrelin. Ghrelin is a hormone that’s “used” by the digestive system to simulate feelings of hunger.
What were the basic results?
Rats that drank tap water or flat soda weighed significantly less than those drinking the carbonated drinks. Rats that drank both the diet and sugary fizzy drinks gained a similar amount of weight. Weight gain was slowest in the water-drinking rats compared with all three groups drinking soda.
Rats drinking the fizzy drinks ate significantly more food than those drinking water and flat soda. This was associated with increased blood levels of ghrelin, further supported by evidence of increased ghrelin secretion from the stomach.
There was no difference in blood sugar or cholesterol levels, but those that drank fizzy drinks had more fat in the liver.
In the human volunteers, ghrelin levels were higher after drinking fizzy drinks one hour after food – three-folds higher than after flat soda, and six-folds higher than after water.
How did the researchers interpret the results?
The researchers concluded that, “This study clearly shows discernible effect of the carbon dioxide gas in carbonated drinks on increased food ingestion and heightened risk of weight gain, obesity and fatty liver disease by inducing ghrelin release.”
There seemed to be a clear distinction in this study between fizzy and non-fizzy-drink consumption in terms of weight gain, appetite and ghrelin production.
These findings were further supported by the study in healthy adult volunteers, which similarly showed that the fizzy drinks increased ghrelin production.
But does this mean that carbonation and ghrelin production provide the whole answer to why soft drink consumption is linked with obesity?
But this doesn’t account for the link between weight gain and diet drinks which don’t contain sugar’They suggest carbonation could be the common link between the two.
This is possible. But it may also be that other unhealthy lifestyle factors, which this study didn’t look at, could also be a common link between sugary and diet fizzy drinks..
In real life, people who drink soda lots of fizzy drinks could also be more likely to have a less healthy diet and exercise less.
It could still be argued that even if people drinking soft drinks do eat more unhealthy food, this is caused by the carbonation making them eat more, but this isn’t proven.
Another point to bear in mind is that this research was conducted primarily in rats. Human beings may not have identical biology.
And although the researchers did follow this up with a human study, they only looked at a very small sample of young men. We can’t necessarily apply their results to women or other populations.
Even in the rats, they found though the rats had increased levels of the appetite hormone, there was no effect on the levels of another satiety hormone that tells them they’re full. This means we can’t be certain that ghrelin provides the whole answer to weight gain.
Overall, this study raises an interesting possibility that fizzy drinks could stimulate the appetite and cause weight gain, which is definitely worthy of further research.
The best way to achieve a healthy weight is through eating a balanced diet and exercising regularly And as unexciting as it may seem, water straight from the tap is the best option to quench your thirst.