But while we all might wish it was this easy to lose weight, unfortunately there's little evidence to back up these claims., of 14 young adults, found drinking 500 ml of water increased resting energy expenditure by about 24 percent.
While this may sound great, this effect only lasted an hour. And this wouldn't translate to a big difference at all. For an average 70 kg adult, they would only use an additional 20 calories – a quarter of a biscuit – for every 500 ml of water they drank.of eight young adults only saw an increase in energy expenditure when the water was fridge cold – reporting a very modest 4 percent increase in calories burned.
This may be because the body needs to use more energy in order to bring the water up to body temperature, or because it requires more energy for the body to filter the increased volume of fluid through the kidneys. And again, this effect was only seen for about an hour. So although scientifically it might be possible, the actual net increase in calories burned is tiny. For example, even if you drank an extra 1.5 liters of water per day, it would save fewer calories than you'd get in a slice of bread.
It's also worth noting that all this research was in young healthy adults. More research is needed to see whether this effect is also seen in other groups .This claim again seems sensible, in that if your stomach is at least partly full of water there's less room for food – so you end up eating less.