I’m Working Out—So Why Am I Getting Fatter?

This week on Fat Science, Dr. Emily Cooper, Mark Wright, and Andrea Taylor talk with exercise physiologist Russell Cunningham and patient Becca Wert about a counterintuitive reality: for some people, exercise can actually slow metabolism, stall weight loss, and trigger weight gain—especially when the brain senses a threat to energy availability. Dr. Cooper explains how overtraining, under-fueling, and even thinking about workouts can activate famine signals in the brain and shut down key hormone pathways and what it takes to rebuild trust so movement becomes helpful instead of harmful. Key Questions Answered How can exercise trigger metabolic slowdown and weight gain instead of weight loss? What lab markers (leptin, ghrelin, thyroid, cortisol, sex hormones) signal that your body is in “conservation mode”? Why did Becca lose more than 120 pounds after stopping intense workouts—and what did her COVID experience reveal about her metabolism? How did Russell’s overtraining syndrome develop, and what did his recovery teach him about fueling, rest, and nervous system regulation? How should fueling before, during, and after activity look different for people who are highly sensitive to energy deficits? When is it time to pull back on exercise, even if every message you’ve heard says “move more”? Key Takeaways Exercise is stress, not magic. When the brain perceives low energy or famine risk, it can respond to exercise by slowing metabolism, shutting down hormones, and defending body fat. Labs tell the story. Low leptin with high “famine signals,” along with thyroid, cortisol, and reproductive hormone suppression, are red flags that the body is conserving energy—not freely burning fuel. Fueling beats punishment. For sensitive metabolisms, you often “can’t overdo the fueling” around movement—sports drinks and carbs, even for short sessions, can help reassure the brain that it’s safe. Movement ≠ grind. Reframing exercise as enjoyable movement and nervous system regulation (walking, gentle climbing, yard work) helps break from all-or-nothing “training” mindsets that can backfire. Dr. Cooper’s Actionable Tips If your weight climbs or stalls despite hard workouts and restricted eating, talk with a clinician about metabolic labs instead of just pushing harder. Cushion any exercise with real fuel: eat before, add carbs/electrolytes during, and refuel after—especially if you have a history of dieting, overtraining, or weight cycling. Consider starting with low-intensity, pleasant movement and always “leave gas in the tank” instead of chasing exhaustion as the goal. Notable Quote“Exercise should not be used as a weight loss tool. It should be used as a performance and a health tool.” — Dr. Emily Cooper Links & ResourcesPodcast Home: Fat Science Podcast Website – https://fatsciencepodcast.com/Cooper Center for Metabolism & Fat Science Episodes: https://coopermetabolic.com/podcast/Resources and education from Dr. Cooper: https://coopermetabolic.com/resources/Submit a Show Question: [email protected]. Cooper direct show email: [email protected] Fat Science is your source for breaking diet myths and advancing the science of true metabolic health. No diets, no agendas—just science that makes you feel better. The show is informational only and does not constitute medical advice.