A tough leg day may have an unexpectedly simple boost: the smell of chocolate. According to a new study published in Frontiers in Physiology, exposure to chocolate aromas before and during resistance exercise helped participants complete more repetitions without making the workout feel more difficult.
"Exposing moderately trained men to chocolate odors right before and between sets of resistance exercise significantly increased their overall training volume without increasing their perceived exertion," said senior author Dr. Mohamed Nashrudin bin Naharudin, an assistant professor at the Faculty of Sports and Exercise Science at the University of Malaya. "Seeing a substantial increase in repetitions without the athletes feeling like they were exerting themselves any harder is a fascinating psychobiological outcome."
Testing Chocolate Scents During Exercise
The study included 23 healthy men in their early to mid-20s who were moderately trained. Researchers separated them into three groups and exposed each group to one of three samples: liquified dark chocolate containing 90% cocoa, liquified milk chocolate containing 60% cocoa, or water as a control.
"We know olfaction is powerfully wired into the brain's appetite and emotion networks, but surprisingly, no study has systematically looked at the three-way interaction between smell, appetite, and actual resistance exercise capacity," said Nashrudin Naharudin.
Before exercising, the participants had gone without food for at least 10 hours. They then performed leg extensions, an exercise in which a person sits and straightens the lower legs against resistance to lift a weight.
Researchers measured leg extension performance both before and during the training session. Before exercising, participants also rated their hunger, fullness, desire to eat, and intention to eat in the near future. While completing their sets, researchers measured hunger and desire to eat after each 30-second exposure to one of the scent samples.
Dark and Milk Chocolate Produced Different Effects
The two chocolate aromas influenced appetite in notably different ways.
Compared with both the water control and milk chocolate conditions, smelling dark chocolate was consistently associated with lower hunger, less desire and intention to eat, and greater feelings of fullness before exercise. The dark chocolate aroma therefore appeared to reduce appetite mainly by decreasing hunger and increasing perceived fullness.
Milk chocolate had a different effect. Participants rated its smell as more pleasant than either dark chocolate or water, but the aroma did not significantly change their hunger or appetite.
The effects were not limited to appetite. Chocolate aromas also appeared to influence how much exercise the participants could complete.
"Sniffing a 90% dark chocolate odor added about 18 more repetitions to participants' leg extensions, while a 60% milk chocolate odor added about nine repetitions compared to the water control," said Nashrudin Naharudin.
How Smell Could Influence the Brain
The researchers think learned associations with food may help explain the results. From an early age, people repeatedly experience certain smells alongside eating. Over time, those aromas can become signals that lead the brain and body to anticipate what normally happens after food is consumed.
Those expectations may even shift a person's perception from hunger toward fullness before any food has actually been eaten.
"The dark chocolate scent serves as a learned cue for a rich, bitter, and highly satiating food, which essentially tricks the system into an anticipatory state of fullness," said Nashrudin Naharudin. "Conversely, the sweeter milk chocolate scent acts more like a hedonic reward cue, enhancing training volume by creating a highly pleasant sensory environment rather than by shifting basic metabolic hunger signals."
The findings raise the possibility that simply anticipating food could trigger some responses resembling those caused by actually eating it. That possibility is especially intriguing because the participants had been fasting when the effects were observed.
Food aromas may prepare the digestive system for an upcoming meal or produce psychological and physiological changes as the body anticipates eating. Some of these responses could resemble changes that normally happen after food consumption.
Important Limitations of the Study
The researchers caution that the biological explanation remains speculative. They did not measure blood hormones or neural activity, so the study cannot 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 dark and milk chocolate aromas may not have been perfectly identical. Because the control sample was odorless water, participants also may have realized when they were in the control condition.
The study was also small and included only healthy, moderately trained young men. Research involving larger and more diverse groups will be needed to determine how broadly the findings apply.
Could Other Food Smells Work Too?
Another unanswered question is whether chocolate has something special about it or whether other familiar foods could produce similar effects.
"We don't think chocolate is entirely unique, though it is a food cue with incredibly strong, universally recognized reward associations," Nashrudin Naharudin concluded.
Other foods strongly associated with feeling satisfied after eating might potentially produce comparable responses, although researchers have not yet tested that idea.
"A person likely needs to find the odor familiar and appealing - or at least not repulsive - to trigger the psychological shift in appetite that's needed to see a performance boost."