Advice to drink water with a meal to feel full may not work as simply as it sounds. Meanwhile, adding some heat to food could slow eating and reduce how much people consume, at least under controlled laboratory conditions.
The findings come from two separate studies, published in Appetite, led by researchers at Cornell University and Penn State. The evidence was stronger for the spicy-food experiment, in which participants were deliberately served mild and spicy versions of the same snack. The water finding came from a secondary analysis of existing meal data and cannot show that drinking more water caused people to eat more.
Neither study measured weight loss or long-term eating habits. They instead examined how small changes in the experience and rhythm of eating affected intake during individual laboratory meals.
The research received federal support and an unrestricted gift from the McCormick Science Institute, an organization that funds research on culinary herbs and spices. The funders had no role in the study design, data collection, analysis, interpretation, writing or publication decision.
For the water analysis, researchers pooled data from two previous laboratory experiments involving 86 adults. Participants were given water and allowed to eat as much as they wanted of either beef chili or chicken tikka masala while cameras recorded every bite and sip.
People who drank more water during the meal also tended to eat more food. For each additional 100 grams of water consumed, participants ate about 39 additional grams of food, or roughly 49 more calories.
Participants who switched more frequently between food and water also ate more. Each additional transition from a bite to a sip or a sip to a bite was associated with about 4.4 more grams of food consumed. The paper was published in Appetite.
Researchers proposed several possible explanations. Water may make dry or thick foods easier to swallow, allowing people to eat more comfortably or quickly. Taking a sip may also briefly interrupt the taste and texture of a food, making the next bite feel more appealing.
That could delay sensory-specific satiety, the gradual decline in enjoyment that often occurs as someone continues eating the same food. Alternating between food and water may create enough contrast to slow that decline.
“There’s been this widespread advice that if we drink water, it fills us up,” said Paige Cunningham, an assistant professor in Cornell’s Division of Nutritional Sciences. “But water is emptied quickly from the stomach so it likely doesn’t fill us up for long.”
Those explanations remain hypotheses. Participants were not randomly assigned to drink specific amounts of water or follow particular bite-and-sip patterns. Researchers simply observed the behaviors that occurred and looked for relationships with food intake.
People who ate more may have needed more water because they consumed more bites. Longer meals also gave participants more opportunities to both eat and drink. Personal eating styles or the moisture and spice level of the foods could have influenced both behaviors.
Another result complicated the picture: Participants who drank their water more quickly tended to eat less, not more. Researchers could not determine whether faster drinking directly affected fullness or merely reflected other differences in meal length and eating behavior.
“This was a secondary analysis looking at associations,” Cunningham said. “We are following up on this right now so we can make those causal inferences.”
The study also examined water consumed during a meal. It did not test whether drinking water shortly before eating affects hunger or food intake, so it should not be used to dismiss all advice involving water and appetite.
The spicy-food study offered stronger evidence of a direct effect, although it was smaller and limited to one type of snack.
In that experiment, 49 adults were served tortilla chips with salsa during two laboratory visits. They received a mild salsa during one session and a spicier version during the other. The amount of cayenne pepper changed, but the rest of the snack remained the same.
Participants ate about 28% less of the total snack when the salsa was spicier. The reduction included both salsa and chips, even though the chips themselves were unchanged.
They also ate the spicy snack about 30% more slowly. Water intake did not differ between the mild and spicy conditions, suggesting that participants did not eat less simply because they filled up on additional water.
“We were interested in whether making the salsa spicy would result in people eating the same amount of chips,” Cunningham said. “And they didn’t.”
The crossover design, in which each person tried both versions, helps reduce the influence of individual differences in appetite and eating habits. It supports the idea that the additional heat changed eating behavior during this particular snack.
The experiment does not show that spicy foods produce weight loss or consistently reduce intake outside the laboratory. It involved only 49 adults, two snack sessions and one combination of chips and salsa. A food that becomes unpleasantly hot could also reduce intake because people do not enjoy it, rather than because it promotes fullness.
The findings are better understood as evidence about eating rate. Slower eating gives the body more time to register signals related to fullness, but people’s responses depend on the food, the degree of heat and their tolerance for spice.
“Both studies show how mealtime behaviors and food properties can significantly influence how much we eat, without us even realizing,” Cunningham said.
They do not support replacing one universal diet rule with another. Drinking water remains important for hydration, and these results provide no reason to avoid water with meals. Adding cayenne pepper is also not a proven weight-management treatment.
Instead, the studies suggest that the pace and sensory rhythm of a meal may help shape when people stop eating. Food texture, moisture, heat and the pattern of bites and sips may all matter, but their effects will need to be tested across more foods and in everyday settings.
The research was supported by faculty-controlled discretionary funds and federal appropriations through the Hatch Act from the U.S. Department of Agriculture’s National Institute of Food and Agriculture. The work also received an unrestricted gift from the McCormick Science Institute, which funds research into culinary herbs and spices.