A food smell, a cooking video, pizza chewed and spat out: 24 studies asked if the senses can stir appetite. Mouths watered, but who ate more is unclear, and the volunteers were mostly healthy

Your body starts getting ready for a meal before the first bite. Saliva flows, and insulin can rise a little, in what physiologists call the cephalic phase response. A hospital nursing and radiotherapy team in Suzhou, China, wanted to know how far that could be pushed, and which sense does it best. Their review, published in The Journal of Nutrition, Health & Aging on 26 October, opens with the problem of people who don't eat enough, including older adults and cancer patients.

They searched five databases up to 1 May 2025 and went from 8,094 records to 24 studies in 22 reports, with 1,008 adults. The tests were an odd and likeable mix. Ambient smells of beef, chocolate, melon or cucumber. Cooking videos of shrimp in chili sauce. Pasta in three shapes at one lunch. Luncheon meat, hard or soft, eaten at a cinema. And modified sham feeding, where people chew a peanut butter sandwich, cream cheese or cheese pizza and spit it out.

The firmest result is the least surprising: food cues make your mouth water. Two randomised trials pooled to a standardised mean difference of 1.04, which is a large effect on the usual rule of thumb. Those two trials had 45 people between them, by our count from the paper's table, and the review rated them as raising some concerns about bias. Five non-randomised studies could also be pooled on saliva. In those, taste (1.03) and touch or chewing (1.12) clearly raised flow. Smell alone (0.37) didn't reach significance.

Hunger is where the gaps show. The pooled appetite figure of 0.54 comes from four non-randomised smell studies, all listed in the paper's table as women only: 123 of them, on our count. All used rating scales, which the authors say may not reflect real changes in appetite regulation. The only randomised trial touching appetite had 12 young adults and found that a picture and a smell together worked better than either alone. It couldn't be pooled with anything.

Eating more is less certain still. Three randomised trials pooled to 0.32, with an interval running from a small reduction to a large rise (-0.25 to 0.88) and very high disagreement between them. They tested texture, texture with sweetness, and the look of pears and peppers. None tested smell. In one, soft textures led to more eating; in the cafeteria trial, varied shapes and colours of pears and peppers made no overall difference. The non-randomised studies gave a small positive figure of 0.19, but it stopped being significant when certain single studies were removed, and smell's own subgroup (0.20) wasn't significant either.

Insulin looks like the best story and has the thinnest evidence. Four non-randomised studies, 102 people on our count, pooled to 0.95, again losing significance when certain studies were dropped. One taste study found a rise with sucrose and saccharin, but not with sour, salty, bitter or umami tastes. And a 1980 study found insulin rose at the sight and smell of a meal in women with obesity but not in healthy women, which the authors take as a hint that the person matters as well as the cue.

The bigger issue is who was tested. The authors describe the people as predominantly healthy, with two groups of women with obesity. Reading the review's table, we can't find a group picked for poor appetite or malnutrition. The oldest group, 25 people averaging 72, was only tested on saliva. Most tests were one-off lab sessions lasting seconds to minutes. So the idea that a smell before dinner might help someone who has stopped eating remains a reasonable idea with no test behind it here. The authors say as much: they call for trials in at-risk groups, and for checking whether nutrition actually improves.

It also matters which way you read this. The same studies that raise hopes for poor eaters include bread smell raising appetite and intake in women with obesity. More appetite is only good news if you need it. And the review can't tell you what any of this means in a real kitchen: its authors say the laboratory settings leave real-world eating uncertain, and no eligible study looked at sound at all.