Drinking a large glass of water with a meal really does trick the brain into thinking you are full, researchers say.
A new study has, for the first time, combined three sets of data to work out what happens when a large glass of water is drunk.
A team from Wageningen University in the Netherlands looked at stomach MRI scans, MRI scans of the brain and recorded how full people said they felt.
Some 19 people took part in two different sessions. All consumed a milkshake followed by either a small (50ml) or large glass of water (350ml).
The stomach MRI scans showed the large glass of water doubled the stomach content size compared with the small glass.
At the same time, those people who had drunk the large glass reported feeling fuller and less hungry.
An area of the brain called the mid-temporal gyrus also showed activity that was in some way influenced by the increased water load.
Guido Camps, lead author of the study, said the research would be used to inform strategies looking at how drinking water with a meal could help people feel fuller sooner.
He added: "In conclusion, we've found that simply adding water increases stomach distension, curbs appetite in the short term and increases regional brain activity."