The smell of chocolate can make you want something sweet. But can it change not just how much you feel like eating, but how much you actually eat?
A 2017 study used four food odors dispersed in a room to examine self-rated appetite, saliva and food intake within the same experiment. Participants ate more of the test meal in the presence of chocolate odor than in the odorless condition. Yet their answers about wanting to eat and the changes in how much they ate did not follow exactly the same pattern.
Studying “Wanting to Eat” and “Having Eaten” Together
The aim was to investigate how food odors change eating behavior and the body’s preparatory responses. The researchers focused particularly on the energy density of the foods suggested by the odors, and on whether those foods were sweet or savory.
Chocolate and beef, for example, were on the high-energy side, and melon and cucumber on the low-energy side. Meanwhile, chocolate and melon fell on the sweet side, and beef and cucumber on the savory side. This combination makes it possible to examine whether eating more of a chocolate-flavored test meal reflects a match with a sweet odor or an association with energy-rich foods.
“High-energy odor” does not mean taking in nutrients by inhaling the smell. It refers to the characteristics of the food signaled by the odor.
32 People Ate the Same Meal under Five Room Conditions
Participants were 32 women with a normal sense of smell, a BMI in the normal range and no strong tendency to restrict their food intake. Their average age was about 21. People who disliked the odors or the test meal were also excluded during screening.
Each participant visited five times on separate days and experienced all five conditions: chocolate, beef, melon and cucumber odors, and no odor. The order was randomized, although the sequences of conditions were not fully balanced. Participants attended at roughly the same time of day on each visit and refrained from eating for the preceding three hours.
The odors were dispersed by devices in the rooms and adjusted to be detectable without being too strong. This was checked with 80 people separate from the main study. Participants were not told that the effects of odor were the central focus of the research.
First, in an odorless room, participants rated their appetite and provided a saliva sample by holding cotton under the tongue for one minute. They then entered the test room and rated how much they wanted to eat 15 foods after 1, 8 and 15 minutes. Saliva was collected again after 3 and 10 minutes.
About 30 minutes later, they were served sweet chocolate rice made with ingredients including rice, milk, sugar and cocoa. A 600 g portion was provided, and they could eat freely until comfortably full. Since the test meal was the same on every visit, the comparison concerned differences in ambient odor, not differences in the dish.
With Chocolate Odor, Participants Ate about 39 g More
Average intake was about 246 g in the chocolate-odor condition and about 207 g in the odorless condition. The difference of about 39 g was statistically significant. Intake was also higher than the approximately 194 g eaten in the melon-odor condition.
With beef odor, intake was about 242 g, but the difference from the odorless condition did not reach significance. The difference from the melon-odor condition, however, was significant. These findings do not allow us to lump chocolate and beef together as both having definitively increased intake compared with no odor.
When chocolate and beef were grouped together as odors of high-energy foods, intake was about 244 g. This was higher than both the approximately 207 g for melon and cucumber combined and the approximately 207 g in the odorless condition. When the odors were grouped as sweet versus savory, however, there was no significant difference in intake.
In this experiment, associations with energy-rich foods may have been more closely linked to the amount eaten than a match with the test meal’s sweetness. The researchers offer associations between odors and nutrients learned through eating experience as one possible explanation.
Appetite and Saliva Showed Different Results
Appetite ratings were generally higher in all four odor conditions than in the odorless condition. However, the study did not find specific appetite for food groups corresponding to the odor, such as wanting only chocolate or cake when exposed to chocolate odor.
In the initial saliva analysis, production was higher under chocolate and beef odor than under no odor. Grouping the high-energy food odors together also gave higher values than the low-energy group or the odorless condition. The sweet group had higher values than the odorless condition, but the direct sweet-versus-savory comparison was not significant.
However, familiarity with the experiment also seems to have played a part in salivation. On the first visit, participants produced more saliva and ate less than on later visits. When the data were reanalyzed taking visit order into account, the effects of odor on food intake and appetite remained, but the differences in saliva between odor conditions no longer reached the significance threshold.
The condition-specific means for saliva and appetite also include measurements taken before odor exposure. They cannot be read as showing that everyone’s saliva increased by a fixed amount immediately after smelling the odor. In fact, saliva production declined over successive measurements.
How Should We Think about the Scents around a Meal?
What makes this study interesting is that it captured differences in food intake associated with ambient odors that self-reported appetite alone would not reveal. Even though appetite was higher with all four odors, the differences in the amount eaten were not the same. This shows the value of measuring feelings, bodily responses and behavior separately.
On the other hand, there was only one test meal: sweet chocolate rice. The chocolate odor itself was also liked more than the other odors. These results come from a group consisting mainly of young women who did not dislike the odors or the dish, so they cannot be applied directly to meals involving likes and dislikes, or to a wide range of ages.
The researchers also mention the possibility of using odors to guide people toward desirable eating patterns in the future. That would require investigating, among other things, whether the same relationship holds for low-energy dishes and whether it lasts over time. These results do not establish a method of weight management through odors; rather, they offer a way to think about sensory cues that come from beyond the table.
Summary
In this experiment, ambient chocolate odor increased intake of chocolate rice compared with no odor. There was also a difference when high-energy food odors were grouped together, but none when odors were classified as sweet or savory.
While appetite increased broadly with the four odors, specific appetite for particular foods was not demonstrated, and the saliva findings weakened when visit order was taken into account. We can understand the relationship between scents and eating more concretely by separating “feeling that something seems appetizing,” “the mouth watering” and “actually eating.”
The research was funded by the Netherlands Organization for Scientific Research (NWO), and IFF supplied the odors. The authors declared no conflicts of interest.
References
Proserpio C, de Graaf C, Laureati M, Pagliarini E, Boesveldt S. (2017). Impact of ambient odors on food intake, saliva production and appetite ratings. Physiology & Behavior. Original paper / Author-accepted manuscript
