Drinking water with lunch may lead to eating more

A glass of water with lunch is often thought to help people eat less. The idea is that the stomach expands, fullness comes earlier and the fork is put down sooner.

Paige Cunningham of Cornell University and John Hayes of Penn State combined lunch videos from 86 adults and calculated how much water each participant consumed. Those who drank the most water also ate the most food.

Water ranks third among diet tactics

In a national health survey of 48,026 adults, 42 percent reported that they were trying to lose weight. Drinking extra water was the third most common strategy they mentioned, after eating less and being more physically active.

Cunningham, an assistant professor in the Division of Nutritional Sciences, pointed out that fullness is short-lived. “But water is emptied quickly from the stomach,” she said.

She and Hayes wrote that research has never substantiated the theory. The small number of studies that have examined it have produced conflicting results.

A 2007 study reported that water lowered food intake, but only for older adults and only when they drank it before sitting down to eat, rather than during the meal.

A far earlier study, published in 1981, reached the reverse conclusion. It applied only to people with above-average weight and involved groups so small that the difference may not have been meaningful.

Chilli, tikka masala and a camera

The 86 adults had taken part in two previous experiments. Fifty-two ate beef chilli, while 34 were served chicken tikka masala. Every participant ate the same dish on two occasions, creating footage from 172 lunches.

Each person was given a 650-gram portion and almost 450 grams of water, then allowed to eat and drink as much as they wished.

For the different visits, Cunningham and Hayes varied the heat by combining hot paprika and sweet paprika in changing proportions.

Researchers then reviewed the recordings. They logged every sip, estimated how large it was, measured the speed at which water was drunk and counted each move from a bite of food to a sip of water.

More water, more food

For each additional 100 grams of water consumed - slightly under half a cup - participants ate around 39 grams more food. That is equivalent to roughly 49 calories.

Cunningham said water could function as a lubricant, helping people eat more quickly. It might also prevent the mouth from becoming dry, meaning food stays pleasant for longer.

The next result was not what Cunningham and Hayes expected. People who drank water more quickly ate less, rather than more, food.

They do not yet know why. Slow sipping may keep water in the mouth for longer, or the relationship could instead be explained by meals lasting longer.

A 1978 study found the opposite pattern, with people of above-average weight drinking more quickly during meals than lean people.

Bites, sips and back again

People partly stop eating because food becomes less enjoyable as a meal continues. The first bite of chilli tastes better than the twentieth.

Cunningham and Hayes believe that a mouthful of water may disrupt this process. The food becomes appealing again, so people continue eating.

One additional switch between food and water was linked with eating about 4.4 grams more food. On its own, that is almost negligible. However, people move repeatedly between bites and sips during a meal, and those grams can accumulate.

Cunningham and Hayes characterise switching as a habit that could lead people to eat more than they require.

Before this research, scientists had studied adults using just one food: the macaroni cheese used by Cunningham’s group in 2023. A separate team identified the same pattern in children the next year.

In 2025, Cunningham’s group associated more frequent switching with a year of fat gain among children from families at high risk of obesity.

Spice slowed people down anyway

Chilli peppers cause their burn through a single chemical: capsaicin. Most people reach for water to ease the heat and, although other drinks are more effective, water remains better than nothing.

This prompted a question. Cunningham and Hayes had already demonstrated that spicier food makes people eat more slowly and leaves more food in the bowl.

If water relieves the burning sensation, people drinking alongside a spicy meal should be able to eat as much as they would with a mild dish. In that case, spice would no longer act as a brake.

That was not what happened. Spice slowed all participants by the same degree, irrespective of their water-drinking habits or how often they alternated between bites and sips.

What two lunches cannot show

Because this analysis used data gathered for a different purpose, it identifies associations rather than showing what caused them.

“This was a secondary analysis looking at associations,” said Cunningham.

People who eat more may simply drink more water. The video evidence cannot establish which happens first.

The meals were also limited to two dishes eaten in a laboratory. Cunningham and Hayes caution against assuming that the same relationship applies to very different foods or to eating habits at home.

The next experiments have been designed to examine cause and effect. “We are following up on this right now,” Cunningham said.

The complete study appeared in the journal Appetite.