Brief exposure to the odor of dark chocolate allowed fasting men to increase the number of resistance exercises they performed while reducing hunger, providing early evidence that food-related odors can influence training performance without burning calories.
Study: Chocolate odor improves resistance exercise performance through appetite suppression in the fasted state: an exploratory study. Image credit: Beats1/Shutterstock.com
recent Frontiers in physiology This study investigated whether exposure to chocolate-related odors alters appetite perception, odor pleasantness, and resistance exercise performance in moderately trained fasted men.
Chocolate smell may affect hunger and athletic performance
Resistance exercise is widely used to build strength and muscle, but training on an empty stomach or during calorie restriction can make your workout seem more difficult and reduce your performance. This has traditionally been thought to be due to a decrease in available energy, but researchers are increasingly interested in whether hunger itself also plays a role.
Previous research has shown that simply changing satiety without providing additional calories can affect exercise performance. This suggests that appetite may influence training through psychological as well as physiological pathways.
One way that your appetite can be influenced is through your sense of smell. The brain’s olfactory system is closely connected to areas involved in appetite and emotion, so food scents can affect hunger and eating behavior. Sweet, familiar scents, such as milk chocolate, are associated with increased appetite, while darker, bitterer chocolate scents may promote satiety.
Researchers have independently investigated how food smells affect appetite, mood, and physical performance, but few studies have investigated whether these effects are related. Understanding this relationship may help identify simple non-dietary strategies to support athletes training while fasting or restricting caloric intake.
The study compared dark, milk and control odors.
The current randomized, double-blind, cross-over study investigated whether the specific aromas of 90% dark chocolate (90DC), milk chocolate (60MC), and non-food control (CON) influence resistance exercise performance by influencing appetite. In a repeated-measures crossover design, participants were exposed to these odors while their appetite, odor pleasantness, and leg-stretching performance were measured.
A total of 23 healthy men participated in this study, with an average age of 23 years and a body mass index (BMI) of 22.4 kg/m2. All participants were non-smokers, but He habitually consumed breakfast, reported no aversion to cocoa-related or sweet food odors, and had trained with resistance exercise at least twice a week for the past 2 years. Individuals with anosmia, substance abuse problems, metabolic or cardiovascular disease, or injuries that could affect performance were excluded.
Participants completed five laboratory visits separated by at least 4 days. The main result was complete repetition. Secondary outcomes include number of sets, repetitions per set, perceived exertion, appetite rating, and odor pleasantness.
During the first visit, participants completed a warm-up and 10 repetition maximum (RM) test on a leg extension machine to measure exercise load. The second visit introduced study procedures such as odor exposure and appetite assessment.
Appetite was measured using a 100 mm visual analogue scale for pre-exercise hunger, satiety, desire to eat, and future food intake, but only hunger and desire to eat were assessed between exercise sets.
Chocolate scent increases resistance momentum
All 23 participants completed the study, and pre-study diet and fasting periods were comparable for all three conditions. Repeated 30-second exposure to 90% dark chocolate odor during 15 minutes before exercise consistently decreased hunger and appetite, increased satiety, and decreased anticipated food intake compared to both 60MC odor and control.
Despite these appetite-related changes, participants did not find the dark chocolate odor significantly more pleasant than the milk chocolate or control conditions. Instead, the milk chocolate scent was rated as most pleasant throughout the pre-exercise period, suggesting that the appetite-related effects observed with the dark chocolate scent cannot simply be explained by how pleasurable participants found the scent.
Participants exposed to the 90DC odor completed the most repetitions, followed by those exposed to the 60MC odor, and performed the least amount of effort in the CON condition. On average, participants completed 18 more repetitions at 90DC than controls, 9 more repetitions than controls at 60MC, and 9 more repetitions at 90DC than 60MC. Participants in the 90DC condition also completed more sets than participants in the other two conditions, but there were no differences between the milk chocolate and control conditions. Taken together, these findings suggest that both chocolate-related odors increased resistance momentum.
After smelling the chocolate odor, participants completed more tasks, but as the exercise progressed, perceived exertion increased similarly in all conditions. However, the authors note that only post-setting ratings of perceived effort were collected, so effects on motivation, fatigue, or other aspects of effort perception cannot be excluded.
Appetite ratings recorded during exercise followed a similar pattern to performance results. Hunger was lowest in the 90DC condition, moderate in the 60MC condition, and highest in the control condition, while desire to eat was also consistently lowest after exposure to dark chocolate odor. In contrast, the milk chocolate odor continued to receive the highest pleasantness ratings throughout the motor task, but there were no differences between the dark chocolate and control conditions.
To examine whether these changes in appetite explained the improved performance, the researchers performed additional analyses. Participants who reported less hunger and greater satiety before exercise generally completed more repetitions and sets, but odor comfort was not associated with performance. However, in an exploratory mediation analysis, we found no statistical evidence that hunger, satiety, and comfort directly explained the differences in motor performance between odor conditions.
Finally, the researchers assessed whether blinding was successful. Participants were typically unable to discriminate between the two chocolate odor conditions, indicating that masking was effective. However, the authors acknowledge that the odorless control was easily recognized and that it may have introduced an expectancy or nocebo-like effect. Therefore, some of the differences observed between the active odor condition and the control may not have been solely caused by the odor itself.
The scent of chocolate shows that fasted training is effective.
The current study highlights the complex relationship between olfactory signals and athletic performance. The observed effects on subjective appetite, odor pleasantness, and physical activity demonstrate the multifaceted effects of food-related odors. However, because mediation analyzes were exploratory and inconclusive, this study did not prove that appetite suppression or odor pleasantness directly caused improved performance.
Future studies should validate the findings in larger and more diverse populations and investigate the underlying mechanisms using comprehensive physiological and neurobiological assessments. The authors also note that the study results were limited to young, resistance-trained men performing a fasted single-joint leg extension task, and that objective hormonal, autonomic, and neurophysiological measurements are needed to determine how food-related odors affect athletic performance. This may provide valuable insights into how sensory stimulation can be leveraged to optimize performance and health during exercise.
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