According to a study by Michael Farrell and his team at Monash University in Australia, our body have a mechanism in controlling our fluid intake, on top of our conscious feelings of thirst. If we are dehydrated, swallowing is effortless; if we are overhydrated, swallowing feels more difficult. Farrell and his team asked a volunteer to rate the sensation of taking a small sip of water, they found that people who had drunk a lot of water took much more effort to swallow than those who were mildly hydrated.
When people were overhydrated, brain scans showed that swallowing was linked with more activity in certain regions of the brain, including the prefrontal cortex, which is responsible for conscious thought processes. Farrell says that the discovery is further evidence that controversial advice to deliberately drink fluids is wrong. Farrell says even people doing exercise just need to drink according to their thirst.