Does Running Make You Gain Weight? 5 Common Myths Debunked

Nutrition experts are debunking social media claims that long-distance running causes unhealthy weight gain. According to nutrition expert Megan Markoff and dietitian Kristy Baumann, weight fluctuations during marathon training often result from glycogen storage and fluid retention rather than fat accumulation, provided nutrition and training are properly aligned.

Megan Markoff responded to a viral Instagram claim that “running made me fat” with a video explaining that training and nutrition are frequently mismatched. Markoff told Runner’s World that influencers often simplify the biological processes occurring during endurance training, which can lead runners to avoid marathons due to fear of weight gain.

Why does weight increase during marathon training?

Weight gain during endurance training does not automatically indicate an increase in body fat. According to dietitian and running coach Kristy Baumann, the body becomes more efficient at storing glycogen, the carbohydrate reserve used as fuel during exertion.

Baumann states that this glycogen binds with water, leading to a higher number on the scale. Additionally, intensive sessions like tempo runs and strength training cause microscopic muscle tissue damage. The body retains extra fluid during the recovery process, which further contributes to weight fluctuations.

Does eating less during training help with weight loss?

Attempting to accelerate weight loss by reducing food intake during training often backfires. Markoff notes that “diet culture” leads many runners to view exercise as a mathematical equation, causing them to under-eat around their workouts.

Baumann warns that insufficient fueling can dysregulate appetite. This often leads to extreme hunger later in the day, increasing the likelihood that a runner will overeat in the evening. To support performance, Baumann recommends at least 30 grams of carbohydrates before a run and at least 30 grams per hour during longer sessions.

For recovery, Baumann suggests a ratio of three to four parts carbohydrates to one part protein. Examples include Greek yogurt with fruit, chocolate milk, or a sandwich with egg.

How does cortisol affect running and weight?

Some social media influencers claim that exercise-induced cortisol, the stress hormone, causes the body to store fat. Markoff explains that while cortisol rises during training, this increase is functional because it helps release energy from fats and carbohydrates.

A 2015 study in the Journal of Sports Medicine and Physical Fitness found that higher-performing half-marathon athletes actually had higher cortisol levels. Furthermore, a 2022 meta-analysis in Psychoneuroendocrinology concluded that regular exercise can lead to lower daily cortisol levels over the long term.

Markoff states that cortisol only becomes a driver of weight gain in cases of overtraining or inadequate recovery. In these scenarios, a disrupted balance between load and recovery may keep cortisol levels chronically elevated.

Does gaining weight impact athletic performance?

Prioritizing weight loss often conflicts with the goal of improving running performance. Baumann explains that weight loss requires a calorie deficit, which may result in insufficient energy, poor performance, or injury.

A 2024 study published in the British Journal of Sports Medicine followed over 1,000 Boston Marathon participants. The researchers found that athletes with low energy availability due to restrictive eating performed worse and required more medical assistance than those without such patterns.

Runner and content creator Emma Mailer shared on Instagram that under-eating to achieve a lower weight eventually led to a stress fracture. Mailer stated that gaining weight was ultimately the best thing for her sport, noting that a properly fueled body is a faster body.

Runners who continue to follow restrictive eating patterns while increasing mileage could face increased risks of hormonal disruptions, mental exhaustion, and slower recovery times.

Frequently Asked Questions

Does running for a marathon always cause fat gain?

No. According to Kristy Baumann, weight gain is often due to increased glycogen storage and water retention, as well as fluid held during muscle repair, rather than fat accumulation.

What is the recommended carbohydrate intake for long runs?

Kristy Baumann advises a minimum of 30 grams of carbohydrates before training and at least 30 grams per hour during longer sessions.

Can cortisol from running make you gain weight?

According to Megan Markoff, cortisol rises functionally during exercise to provide energy. Weight gain typically only occurs if there is a chronic imbalance between training load and recovery, leading to prolonged cortisol elevation.

Do you prioritize the number on the scale or your energy levels during training?