Common diet tips about water intake and spicy foods could be dead wrong

The common rationale for drinking water at meals is that it physically stretches the stomach, triggering fullness so you don't eat too much.

But a new Cornell study found no support for that idea in practice.

Instead, for every additional 100 grams of water participants drank, they ate about 39 more grams of food - roughly 49 more calories. People who frequently switched back and forth between bites of food and sips of water ate even more: each additional switch was tied to about 4.4 more grams of food consumed.

Researchers suspect this "switching" effect works by delaying something called sensory-specific satiety - the way a food's appeal naturally fades the longer you eat it. Alternating with water may reintroduce contrast that keeps the meal appealing longer, delaying the point at which people stop eating.

"There's been this widespread advice that if we drink water, it fills us up," said Paige Cunningham, assistant professor in the Division of Nutritional Sciences in the College of Human Ecology. "But water is emptied quickly from the stomach so it likely doesn't fill us up for long. Instead, water may increase how much we eat, providing lubrication which can speed up eating, and preventing a dry mouth which can prolong enjoyment of the food."

Cunningham is the corresponding author on the new analysis, published in July in the journal Appetite and conducted with longtime collaborator John Hayes of Penn State's Department of Food Science. In a second related study, the researchers measured the effect of spicy salsa on eating volume - and again found a surprising result.

"Both studies show how mealtime behaviors and food properties can significantly influence how much we eat, without us even realizing. We found that just drinking more water was associated with greater consumption, while adding a bit more spice to a snack slowed eating and decreased how much participants ate," said Cunningham.

The drinking water study pooled data from two earlier lab experiments, 86 adults in all, who ate as much as they wanted of a lunch (either beef chili or chicken tikka masala) served with water, while researchers recorded every bite and sip on video.

One result cut against the researchers' own expectations: Participants who drank water faster during a meal ended up eating less, not more. The paper offers this as a genuine open question rather than a settled explanation, noting it may reflect how long water sits in the mouth, or may simply track with how long a meal lasts overall.

"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."

In a separate experiment, whose results published April in Food Quality and Preference, 49 adults were served tortilla chips alongside a mild or spicy salsa, once a week for two weeks; only the salsa's cayenne content changed between conditions. The spicier version cut total snack intake by 28% - not just of the salsa itself, but of the chips too, even though the chips themselves didn't change.

Participants ate the spicy snack about 30% more slowly than the mild one, which the researchers suspect drove the decrease: Heat slowed people down, and slower eating meant less eaten overall. Water intake during the snack was unaffected by spice level, which the researchers note rules it out as an explanation for the reduced intake.

"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 takeaway is that adding spice to one part of the snack can significantly influence how much people eat overall."

Read together, the two papers make a case that runs against two different strands of popular nutrition advice at once: that water at meals is a simple ally in eating less, and that spicy food is something to approach with caution if you're watching what you eat. This research showed the opposite might be true: water tracked with eating more, and spice tracked with eating less.

"These strategies might help consumers achieve their goals to reduce energy intake," Cunningham said.

Both papers are explicit about their limits: the meals and snacks tested were a narrow set - chili, tikka masala and one chip-and-salsa combination - all eaten in a controlled lab setting, and the researchers caution against assuming the same patterns would hold for very different foods or in everyday, uncontrolled eating.

"We are looking to future experiments that explore what other factors or properties of foods can we leverage to influence behaviors," Cunningham said.