An increasing number of fitness enthusiasts have noticed that exercise does not necessarily stimulate an increase in appetite; rather, it often results in eating less.
This is reflected in an article from Runner's World, where a survey on their Instagram, covering nearly 4,300 participants, showed that 68% of respondents had no desire to eat after a long run or intense workout.
Moreover, those who experience suppressed appetites often share a common characteristic in their choice of exercise—high intensity. Workouts such as 'battle ropes' and 'boxing' have seen an unprecedented surge in popularity over the past two years.
For participants in these classes, feeling not at all hungry, or even slightly nauseous, is a common physiological response after the session.
■ The phenomenon of not feeling hungry after exercise is common for many. The World Health Organization classifies any activity with a metabolic equivalent (METs) more than six times higher than at rest as high-intensity exercise. High-intensity workouts are favored by a growing number of young people for their short duration and high fat-burning efficiency.
A substantial body of research has already demonstrated that exercise intensity is a primary factor in suppressing appetite post-exercise. This is because the intensity of exercise affects the secretion of leptin and ghrelin, two hormones closely associated with appetite. For instance, a study published in 2016 found that after high-intensity exercise, ghrelin (which stimulates appetite) decreased, while peptide YY (which inhibits appetite) increased, leading to a lack of appetite.
In addition to exercise intensity, factors such as the timing of meals after exercise, gender, and thirst can also have varying degrees of impact on post-exercise appetite.
It's important to note that regardless of whether one feels hungry or not after a workout, consuming an appropriate amount of nutrients is more conducive to achieving fitness goals. For example, it's important to replenish carbohydrates promptly after high-intensity exercise, while protein should be consumed after resistance training.
Squat the Most, Feast the Hardest
After a leg workout, a meal of barbecue, beef hotpot, or a seafood buffet is often seen as a well-deserved reward for the effort put into fitness. Consuming high-quality protein in a timely manner after a workout can help repair muscles that have been used and damaged during the exercise. More muscle mass can aid in increasing metabolism, which in turn allows for a greater intake of protein.
On the social platform Xiaohongshu, under the keywords 'fitness' and 'buffet,' Japanese Wagyu and seafood buffets, with their low-fat, high-protein characteristics, have gradually become the standard post-workout meal for fitness enthusiasts. There are countless stories of people 'stocking up' on sea urchin in groups, calling themselves 'Wagyu warriors,' and indulging in hundreds of servings of Wagyu after a workout. Some even treat eating buffets as an opportunity to exercise their leg muscles, with their WeChat step counts reaching their targets after a single meal.
The consensus among fitness enthusiasts is that "eating meat after a workout" and "not eating meat after a workout is pointless."
However, on the other hand, there are also many fitness enthusiasts who report a decrease in appetite after their workouts.
A paper published in Health Psychology [1] supports this view. To study the impact of exercise on fat reduction, researchers conducted an experiment with 130 volunteers. They found that when not exercising, participants were 12% more likely to eat more; however, after 60 minutes of exercise, the probability of participants eating more dropped by more than half, to just 5%. Moreover, for every additional 10 minutes of exercise beyond the 60-minute mark, the likelihood of participants eating more continued to decrease by 1%.
Why Aren't We Hungry After Exercise?
Why do some people feel very hungry after exercise, while others do not?
Extensive research indicates that factors such as exercise intensity, the time interval after exercise before eating, dehydration, and gender all have varying degrees of influence on appetite.
Exercise Intensity
Different intensities of exercise have varying effects on feelings of hunger. Generally speaking, high-intensity aerobic and anaerobic exercises (such as kickboxing classes or interval treadmill running) suppress appetite. In such cases, the longer the duration of the exercise, the longer the side effect of suppressed appetite persists. This effect is mediated through hormones.
Hunger is a sensation sent by the brain, a response from the central nervous system. The central nervous system senses hunger by detecting the concentration of glucose in the blood. In other words, low blood sugar is the root cause of hunger.
Leptin and ghrelin are two hormones closely related to appetite. When leptin decreases, appetite increases; when ghrelin decreases, appetite decreases.
■ The influence of exercise intensity on appetite
A study published in 2009 [2] found that running for 60 minutes caused a decrease in ghrelin (which stimulates appetite) and an increase in peptide YY (which inhibits appetite), resulting in a feeling of fullness. After 90 minutes of low-intensity resistance training, ghrelin decreased, but there was no change in peptide YY levels.
Another study published in 2017 [3] confirmed this hypothesis. Researchers found that after a 10-week experiment with volunteers aged 45-64, leptin levels in the body decreased after low-intensity resistance training, meaning people felt hungry.
It's Not That We're Not Hungry, It's Just Not the Right Time
According to the law of conservation of energy, the energy deficit caused by exercise should theoretically make a person feel hungry, and those who do not feel hungry have simply not reached the right time. In other words, at different times after exercise, a person's perception of hunger also varies.
During high-intensity or prolonged exercise, the body prioritizes blood flow to the working muscles, such as the legs and heart. This means that there is a corresponding reduction in blood flow to the internal organs, and a decrease in blood flow to the gastric mucosa can lead to a decrease in appetite. Once the body returns to a state of calm, its functions return to normal levels, and a person will once again feel hungry.
For example, a paper published in 2020 confirmed this hypothesis. Researchers conducted a study on adolescents aged 12-15 to explore the optimal timing for post-exercise replenishment. They found that exercise performed 45 minutes before lunch, compared to 180 minutes before lunch, resulted in an 11% decrease in energy intake and a 23% decrease in fat intake. This study indicates that as time passes after exercise, people will gradually begin to feel hungry.
On the other hand, after high-intensity exercise, the body's temperature rises sharply, which can suppress appetite to a certain extent. However, once the body returns to a state of calm and the body temperature drops, a person will also begin to feel hungry.
This hypothesis was also confirmed. A study published in PLOS Biology in 2018 [4] discovered a temperature regulation mechanism, where the melanocortin hormone of the ARC POMC neurons, through the activation of TRPV1-like receptors, links the acute increase in peripheral and brain temperature with the acute reduction in food intake. This finding can be used to explain the relationship between the increase in body temperature after high-intensity exercise and appetite.
