When was the last time you went to the gym and found working out a bit harder than expected? Leg day in particular can be tough, but a new Frontiers in Physiology study found a promising trick that might make it easier: sniffing chocolate.
"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."
Whiff of cocoa
The participant sample consisted of 23 healthy, moderately trained men in their early to mid-20s. Divided in three groups, they were provided one of three odor samples: liquified dark chocolate containing 90% cocoa, liquified milk chocolate containing 60% cocoa, or a water sample serving 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.
Participants had not eaten for at least 10 hours before performing leg extensions, a resistance training exercise that's performed by sitting down and extending the lower legs to lift a weight upwards. Leg extension performance was assessed before and during their training. Hunger, fullness, desire to eat, and plans to eat in the near future were reported before the leg workout. During the sets only hunger and desire to eat were measured, each after 30 seconds of exposure to a scent sample.
These measurements showed that both chocolate types had clear but different effects on appetite related measures. Relative to the water control and milk chocolate samples, sniffing dark chocolate consistently led to participants reporting less hunger, reduced desire and intention to eat, and greater fullness before exercise. This smell predominantly suppressed appetite by reducing hunger and increasing fullness. In contrast, those smelling the milk chocolate sample reported higher odor pleasantness compared to dark chocolate and water samples, but no changes in hunger or appetite.
Smelling chocolate samples affected not only appetite-related measures, but also performance.
"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.
Ready, steady, eat
The researchers think these changes in appetite perception could be related to what we learn about smells from a young age. Learned cues, such as foods we've eaten before, generate expectations about what happens after eating and can cause a shift from hunger toward perceived fullness.
"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."
These effects suggest that anticipation of food could have similar effects to its actual consumption, particularly because they're observable when people haven't eaten. Food scents might kickstart the digestive process or trigger changes in body and mind that occur in anticipation of a meal. These changes closely mimic some of the psychological and physiological shifts typically brought on by actual eating.
The authors pointed out that their claims remain inferential, as no blood hormones or neural pathways were measured. Additionally, there may have been slight variations in smell intensity between the chocolate samples, and the water sample was odorless, which could have given participants clues about whether they were part of the control group. Finally, more diverse participant samples are needed to confirm these findings.
This leads to the question of whether chocolate is the only food that can trigger such responses.
"We don't think chocolate is entirely unique, though it is a food cue with incredibly strong, universally recognized reward associations," Nashrudin Naharudin concluded. Although this hasn't been tested yet, other foods strongly linked to satiety could show similar effects. "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."
