A brief smell of dark chocolate was linked with more exercise repetitions in a small trial of fasted, resistance-trained men. The result appeared during repeated leg-extension sets, not across a broad workout or range of athletes.
The exploratory crossover study included 23 healthy men, average age 23, who had lifted weights at least twice a week for at least two years. Each participant completed three test sessions at least four days apart: one with a 90% dark chocolate scent, one with a milk chocolate scent and one with an odorless control.
What the trial found
After an overnight fast of about 10 hours, participants smelled one of the test liquids for 30 seconds before each set. With the dark chocolate scent, they completed 18 more total leg-extension repetitions than with the odorless control. The 95% confidence interval for that difference was 13.8 to 22.1 repetitions, with p < 0.001.
The milk chocolate scent was also associated with more repetitions than the control, but the difference was smaller: nine additional repetitions, with a 95% confidence interval of 4.8 to 13.1 and p < 0.001. Dark chocolate produced nine more repetitions than milk chocolate and amounted to about one additional set compared with either condition.
The workout used sets of 10 leg extensions at 80% of each participant’s 10-repetition maximum. Participants rested for 3.5 minutes and continued until they could not complete a set.
Appetite changed, but it did not explain the result
Before exercise, the dark chocolate scent lowered hunger and the desire to eat while increasing fullness compared with both the odorless control and the milk chocolate scent. Milk chocolate did not reduce hunger and slightly increased the desire to eat. It was rated 3.1 millimeters more pleasant than the control on a 100-millimeter scale.
However, the study’s mediation analyses did not show that hunger, fullness or pleasantness statistically accounted for the extra repetitions. The estimated indirect effect through lower hunger was about two repetitions and was not statistically significant. The effect through fullness was under one repetition, and the effect through milk-chocolate pleasantness was about one repetition; neither was statistically significant.
A within-person analysis found that lower pre-exercise hunger was associated with more repetitions, while greater fullness was also associated with more repetitions. These correlations do not establish whether appetite influenced performance or whether another factor affected both.
Why the finding needs careful interpretation
The three scents were freshly mixed liquids placed in identical glass jars. The dark chocolate mixture contained 90% cocoa chocolate and a small amount of water; the milk chocolate mixture combined dark chocolate with whole milk and was labeled “60% milk chocolate.” Distilled water served as the odorless control. All three liquids contained a small amount of propylene glycol.
Participants smelled the jar 2 to 3 centimeters below the nose using paced breathing. They did this four times during the 15 minutes before exercise and again before every set. The amount of scent reaching the nose was not precisely standardized because the researchers used jars rather than an olfactometer.
The odorless control was readily identified, while participants’ guesses about the two chocolate scents were close to chance. That difference means expectations may have contributed to the gap between chocolate and control conditions. Perceived exertion rose from set to set in all sessions, but it did not differ between scents.
The researchers did not measure motivation, mood, muscle fatigue, hormones, heart rate or brain activity. As a result, the trial does not identify the process behind the performance difference.
How this fits with earlier fasting research
Previous findings on fasting and exercise performance have been mixed. In one study of 16 resistance-trained men, skipping breakfast reduced total back-squat repetitions from 68 to 58 and bench-press repetitions from 40 to 38 compared with eating breakfast. In another study of 16 trained men, a thick semisolid meal was associated with less hunger and about 10% more back-squat repetitions than a thin liquid meal, although bench-press repetitions did not differ.
Other evidence has not found the same pattern. A Brazilian trial in trained young men reported that 12 or 16 hours of overnight fasting increased hunger but did not change strength, jump height or back-squat and leg-press repetitions.
A 2010 study of 12 young women found that smelling 85% cocoa chocolate increased feelings of satiety and linked that response to ghrelin. Separately, a review of 32 studies involving 1,513 participants reported small-to-moderate placebo and nocebo effects on sports performance.
What the result does—and does not—show
This study suggests that a short dark chocolate scent exposure was associated with improved performance on one demanding, single-joint exercise in young men exercising after an overnight fast. It does not show that smelling chocolate improves strength, endurance or performance in other exercises, after eating, or in people who differ from the participants.
The trial was described as exploratory. It was preregistered on the Open Science Framework, although its clinical trial registry entry was filed after the fact. Replication across larger and more diverse groups, with better control of expectations and scent delivery, would be needed to determine how robust the finding is.
AI tools were used to assist with the preparation of this article under our editorial standards.
Leave a Reply