The Rich Roll Podcast Kevin Hall, PhD On The Science & Politics of Weight Loss
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Dec 18, 2025 
Kevin Hall, PhD, a former NIH researcher and physicist, dives deep into the science of weight loss and the troubling role of ultra-processed foods. He challenges common beliefs about metabolism, explaining why diets often fail and how our food environment drives obesity more than willpower. Hall shares eye-opening insights into metabolic adaptation, the complexities of appetite regulation, and the political challenges he faced in research. His honest take on nutrition misinformation and calls for better food policies make this a fascinating listen.
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Metabolic Adaptation During Weight Loss
- Metabolic rate falls during weight loss and often more than expected for the smaller body size.
- Kevin Hall calls this metabolic adaptation and it can persist long after active weight loss.
Slowing Is A Response, Not A Sentence
- Greater metabolic slowing often reflects the magnitude of the intervention, not destiny.
- Hall compares it to tension on a spring: more pull creates more rebound pressure but doesn't alone determine outcome.
Appetite Outpaces Metabolic Drop
- For each kilogram lost energy expenditure falls ~25 kcal/day while appetite rises ~95 kcal/day.
- Appetite-driven intake increases explain far more of weight regain plateaus than metabolic slowing.