Just Smelling Chocolate May Boost Your Workout, Study Finds

You are halfway through a workout. Your legs are tiring, and another set sounds unappealing. Imagine catching the scent of chocolate just as you are deciding whether to keep going.

You cannot eat it. You can only smell it.

Would that change what you can do? In a small experiment, men who smelled chocolate completed more leg extensions than they did with a water-based control. They reported no clear increase in how hard each set felt.

For the study, researchers at the University of Malaya recruited 23 healthy men who had trained with weights regularly for at least two years. Each participant completed three experimental sessions on separate mornings after an overnight fast.

During one session, participants smelled a preparation containing 90 percent dark chocolate. In another session, they smelled a mixture of chocolate and milk that the researchers called milk chocolate. The third involved a water-based control. Everyone tried all three conditions, in different orders.

The men smelled their assigned preparation for 30 seconds at a time before exercising and during breaks between sets. Then they performed repeated leg extensions on a machine until they could no longer complete the required repetitions.

With the dark-chocolate odor, participants completed 18 more repetitions in total, on average, than they did with the control. With the milk-chocolate preparation, they completed nine more. Dark chocolate was also associated with roughly one additional set compared with either of the other conditions.

If you imagine the smell of chocolate making a hungry person crave dessert, the appetite results might surprise you.

Before exercising, the men reported less hunger and desire to eat, and greater fullness, in the dark-chocolate condition.

With the milk-chocolate preparation, they reported a greater desire to eat than with the control, but no clear differences in their other measures of hunger or fullness. They also rated that odor as slightly more pleasant than the control.

Previous research involving young women found that smelling dark chocolate was associated with reduced appetite. Could a change in hunger also help explain the extra repetitions?

Within participants, lower hunger and greater fullness were associated with better performance. But the researchers' exploratory analyses did not establish that those changes caused the difference.

"Appetite is a plausible mechanism, but the present study cannot establish causality," senior author Mohamed Nashrudin bin Naharudin, an exercise physiologist at the University of Malaya, told ScienceAlert.

The milk-chocolate finding makes the puzzle more interesting: repetitions increased even though this preparation did not consistently suppress appetite.

Naharudin said other possible influences include expectations, motivation, and associations people have learned between food and its smell. The study did not measure hormones or brain activity that could directly test the proposed biological mechanisms.

Expectations are particularly difficult to separate from the scent itself.

A staff member who was not involved in testing prepared and coded the mixtures. Neither participants nor the people counting repetitions were told which one was being used, and the assessors did not smell the preparations.

Yet the control had no chocolate scent. When the men later guessed which condition they had received, they identified the control much more readily than either chocolate condition.

"Some participants may have realized that they were receiving the control condition and consequently had different expectations about its effects," Naharudin said.

He emphasized that this is a limitation, rather than evidence that expectations explain the results. A future experiment could use a scented control to help distinguish the two possibilities.

And did chocolate make the workout feel easier?

The men rated their exertion after each set. Those ratings rose as the workout progressed but did not clearly differ between conditions. That does not reveal whether the odors affected motivation or other aspects of fatigue the researchers did not measure.

The experiment also tested just one exercise, after fasting, in a small group of young men accustomed to resistance training. Whether the result holds for other workouts or other people remains unknown.

"I would therefore describe this as preliminary proof-of-concept evidence rather than a recommendation for people to use chocolate odor to improve their workouts," Naharudin said.

For now, a chocolate-scented gym is a delightful thought, not a proven training plan.

But the experiment leaves a question worth researching further: If odors may shape the experience of hunger, could some also change when we decide our muscles have done enough?

The study was published in Frontiers in Physiology.