A tough leg day can have an unexpectedly simple boost: the smell of chocolate. According to a new study published in Frontiers in physiologyExposure to chocolate aromas before and during resistance exercise helped participants complete more repetitions without making the workout seem more difficult.
“Exposing moderately trained men to chocolate odors just before and between sets of resistance exercise significantly increased their overall training volume without increasing their perceived exertion,” said lead author Dr. Mohamed Nashrudin bin Naharudin, assistant professor at the Faculty of Sports and Exercise Sciences at the University of Malaya. “Seeing a substantial increase in repetitions without athletes feeling like they were trying harder is a fascinating psychobiological result.”
Chocolate aroma test during exercise
The study included 23 healthy men between the ages of 20 and 30 who were moderately trained. The researchers separated them into three groups and exposed each group to one of three samples: liquefied dark chocolate containing 90% cocoa, liquefied milk chocolate containing 60% cocoa, or water as a control.
“We know that smell is powerfully connected to the brain’s appetite and emotion networks, but surprisingly, no study has systematically looked at the three-way interaction between smell, appetite, and actual endurance exercise capacity,” Nashrudin Naharudin said.
Before exercising, participants had gone without eating for at least 10 hours. They then performed leg extensions, an exercise in which a person sits and stretches their lower legs against resistance to lift a weight.
The researchers measured leg extension performance before and during the training session. Before exercising, participants also rated their hunger, satiety, desire to eat, and intention to eat in the near future. While completing their sets, the researchers measured hunger and desire to eat after each 30-second exposure to one of the odor samples.
Dark chocolate and milk chocolate produced different effects
The two chocolate aromas influenced appetite in noticeably different ways.
Compared to the water and milk chocolate control conditions, smelling dark chocolate was consistently associated with a lower feeling of hunger, less desire and intention to eat, and a higher feeling of satiety before exercise. Therefore, the aroma of dark chocolate seemed to reduce appetite primarily by decreasing hunger and increasing feelings of satiety.
Milk chocolate had a different effect. Participants rated its smell as more pleasant than that of dark chocolate or water, but the aroma did not significantly change their hunger or appetite.
The effects were not limited to appetite. The chocolate aromas also seemed to influence the amount of exercise the participants were able to do.
“Smelling a 90% dark chocolate smell added about 18 more repetitions to the participants’ leg extensions, while a 60% milk chocolate smell added about nine repetitions compared to the water control,” Nashrudin Naharudin said.
How smell could influence the brain
The researchers believe that learned associations with foods may help explain the results. From a young age, people repeatedly experience certain smells along with food. Over time, those aromas can become signals that lead the brain and body to anticipate what normally happens after consuming food.
These expectations can even change a person’s perception from hunger to feeling full before having eaten any food.
“The aroma of dark chocolate serves as a learned cue for a rich, bitter, highly satiating food, essentially tricking the system into an anticipated state of satiety,” said Nashrudin Naharudin. “In contrast, the sweeter aroma of milk chocolate acts more as a hedonic reward signal, improving training volume by creating a very pleasant sensory environment rather than changing basic metabolic hunger signals.”
The findings raise the possibility that simply anticipating food may trigger some responses similar to those caused by actually eating it. That possibility is especially intriguing because participants were fasting when the effects were observed.
Food aromas can prepare the digestive system for an upcoming meal or produce psychological and physiological changes when the body anticipates food. Some of these responses might resemble changes that normally occur after food consumption.
Important limitations of the study
Researchers caution that the biological explanation remains speculative. They didn’t measure blood hormones or neural activity, so the study can’t show exactly which biological pathways were responsible for the changes in appetite and exercise performance.
There were other limitations as well. The intensity of the aromas of dark and milk chocolate may not be perfectly identical. Because the control sample was odorless water, it is possible that participants also noticed when they were in the control condition.
The study was also small and included only healthy, moderately trained young men. Research involving larger, more diverse groups will be needed to determine how widely the findings apply.
Could other food smells work too?
Another unanswered question is whether there is something special about chocolate or whether other familiar foods could produce similar effects.
“We do not believe that chocolate is completely unique, although it is a food signal with incredibly strong and universally recognized reward associations,” concluded Nashrudin Naharudin.
Other foods strongly associated with feeling satisfied after eating could produce comparable responses, although researchers have not yet tested that idea.
“A person likely needs to find the smell familiar and attractive, or at least not repulsive, to trigger the psychological change in appetite that is needed to see an increase in performance.”