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Wide release date: September 12, 2025

Episode Summary: Dr. Christopher Morrison talks about how animals sense and prioritize nutrients like protein, discussing defense mechanisms for essentials such as oxygen, water, sodium, and energy; the brain's role in detecting protein deprivation via signals like FGF21; trade-offs between growth, reproduction, and longevity under protein restriction; and reconciling high-protein diets for satiety and muscle maintenance with low-protein benefits for metabolic health and lifespan extension.

About the guest: Christopher Morrison, PhD is a professor and researcher at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, where he has worked for over 22 years focusing on nutrition, metabolism, and chronic diseases like obesity and diabetes.

Discussion Points:

* The body prioritizes nutrients hierarchically: oxygen and water first, then sodium, energy, and protein, with weaker defenses for carbs or fats.

* Animals develop specific appetites for deprived nutrients, like salt or protein, often through post-ingestive learning rather than just taste.

* Protein restriction (e.g., 5% vs. 20% in diets) increases food intake and energy expenditure in mice to maintain protein levels, even at the cost of extra calories.

* FGF21, a liver hormone, signals protein deprivation to the brain (via NTS region), driving protein-seeking behavior and metabolic changes; it's essential for low-protein responses.

* Protein restriction extends lifespan in lab animals by suppressing growth signals like IGF-1 and mTOR, but may impair immunity or wound healing in real-world conditions.

* High protein aids satiety, weight loss, and muscle building, but overconsumption may shorten lifespan; optimal intake depends on age, activity, and goals (e.g., not for pregnant or elderly).

* No one-size-fits-all for protein: mild restriction may benefit middle-aged sedentary people for health, while athletes need more; balance avoids excesses.

Related content:

* M&M 106: Diet, Macronutrients, Micronutrients, Taste, Whole vs. Processed Food, Obesity & Weight Loss, Comparative Biology of Feeding Behavior | Stephen Simpson & David Raubenheimer

*Not medical advice.

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* Episode transcript below.

Episode Chapters:

00:00:00 Intro

00:06:10 Nutrient Detection & Adequacy

00:11:11 Fluid & Sodium Defenses

00:16:20 Protein vs Other Macronutrients

00:21:21 Post-Ingestive Learning & Flavors

00:26:34 Hyperphagia on Low Protein

00:31:10 Restriction Effects on Growth

00:36:33 Longevity & Restriction Trade-Offs

00:41:47 Behavioral Changes & Choices

00:46:44 Preference in Choice Experiments

00:53:44 Innate vs Learned Appetite

00:58:39 Protein Digestion & Signals

01:04:40 FGF21 in Fasting & Restriction

01:10:40 FGF21 Knockouts & Relevance

01:15:20 Brain Receptors & Sites

01:20:49 Growth & Longevity Trade-Offs

01:25:04 High Protein Satiety & Muscle

01:30:33 FGF21 Scaling & Future Work

01:35:39 Final Thoughts & Recommendations

Full AI-generated transcript below. Beware of typos & mistranslations!