Part V — Nutrition for Life Stages and Goals

Chapters 23–29

Everything up to this point has been about populations. Averages. What happens, on the whole, to people who eat one way rather than another.

That is how nutrition science has to work, and it is also its central limitation, because you are not a population. You are one person, of a particular age, in a particular body, with a particular sport or absence of one, particular labs, particular medications, a particular pregnancy or absence of one, and a particular diagnosis or fear of one.

The general rules from Parts I–IV are still true for you. They're just not sufficient. A twenty- one-year-old running sixty miles a week and a sixty-eight-year-old with type 2 diabetes and a seventy-nine-year-old losing muscle and a pregnant woman in her first trimester and a man on chemotherapy are all subject to the same physiology and need genuinely different things from it.

This part is where the book gets specific.

The seven

Chapter 23 — Sports Nutrition. Not the supplement-stack version. It starts where athlete nutrition problems actually start: energy availability, and RED-S — Relative Energy Deficiency in Sport — which is upstream of the stress fractures, the missing periods, the stalled progress, and the mysterious fatigue. Then carbohydrate periodization, protein dose and timing, hydration and sodium for athletes, and the short list of ergogenic aids with real evidence (creatine, caffeine, nitrate, beta-alanine, bicarbonate) against the very long list without. Devi's arc lands here.

Chapter 24 — Weight Management. 🚪 The chapter with the worst signal-to-noise ratio in the entire field, written as carefully as I know how. The evidence on losing weight, and the far more important and far more neglected evidence on keeping it off. Set point and settling point. Adaptive thermogenesis, leptin, ghrelin, and the physiological defense of body weight. The National Weight Control Registry. A brief, non-promotional account of medication and surgery. And the threshold concept that reframes every failed diet the reader has been blamed for: body weight is a defended system, not a willpower ledger.

Chapter 25 — Nutrition Across the Lifespan. 🪞 Preconception and pregnancy — folate, iron, iodine, choline, DHA, and the food-safety list that is shorter and better-evidenced than the internet's version. Infancy, and the allergen-introduction guidance that reversed in the last fifteen years, which is a case study in what it looks like when science corrects itself properly. Childhood, picky eating, and the division of responsibility. Adolescence. And aging: sarcopenia, protein requirements that go up while appetite goes down, B12 absorption that declines, and the practical problems of teeth, taste, and eating alone.

Chapter 26 — Nutrition and Chronic Disease. Cardiovascular disease, type 2 diabetes, cancer, and metabolic liver disease. What dietary patterns actually reduce risk, with the trial evidence named — DASH, Mediterranean/PREDIMED, DPP-style lifestyle intervention. The critical distinction between prevention and treatment, which is blurred constantly and dangerously. And the ethics of making dietary claims to people who are frightened and sick, which is the most predatory corner of this entire industry.

Chapter 27 — Gut Health and the Microbiome. 🚪 Both halves, held together: this is genuinely important biology, and almost nothing currently sold to fix it works. What we know (diversity tracks with fiber; short-chain fatty acids are real and do real things), what we're guessing (nearly everything specific), probiotics strain by strain rather than as a category, prebiotics, fermented foods, the narrow legitimate use of fecal transplant, and a commercial testing market running years ahead of the science.

Chapter 28 — Food Allergies, Intolerances, and Sensitivities. ★ Three different things that get one word. IgE-mediated allergy — real, testable, occasionally fatal. Intolerance — real, common, not immune-mediated. "Sensitivity" — a word doing enormous unearned work. Celiac disease and the rule people break constantly: test before you eliminate, because the test requires gluten in the diet to be valid. Non-celiac gluten sensitivity and the FODMAP confound. Lactose intolerance as the global norm. The low-FODMAP diet as a supervised, temporary diagnostic tool rather than a lifestyle. And the IgG food-sensitivity panels that the major allergy organizations explicitly advise against. Alma and Nico sit side by side in this chapter, and the contrast is the whole lesson.

Chapter 29 — Clinical Nutrition. ★ 🪞 What happens when food becomes medicine, administered by professionals. Nutrition screening and assessment. Enteral and parenteral nutrition, and the principle that governs the choice: if the gut works, use it. Refeeding syndrome. Critical care. Oncology nutrition, cachexia, and the specific harm done by "sugar feeds cancer." Renal and hepatic diets. Written for two readers at once: the clinician-in- training who needs to know this, and the person who will one day be standing next to a hospital bed trying to be useful.

How to read this part

Almost nobody needs all seven chapters. This is the most modular part of the book, and it's designed to be sampled.

If you…	Read
Train seriously, or coach people who do	23, 24, 34 (in Part VI)
Are trying to change your weight	24, 33 (Part VI), 34 (Part VI)
Are pregnant, or feeding a child or a parent	25
Have — or are trying to avoid — a chronic diagnosis	26, 24
Have gut symptoms	28 first, then 27
Work in healthcare, or have a family member who's ill	29, 26, 28
Are curious about the microbiome hype	27

Read the ones that describe your life. Skim the rest, or come back when they become relevant — and one or two of them will, eventually, for everyone.

The thing that connects all seven

Requirements change, principles don't.

An older adult needs more protein per kilogram than a young one; the reason is sarcopenia and anabolic resistance, not a different biology. A distance runner needs far more energy than her resting metabolic rate suggests; the reason is energy availability, which is Chapter 4's arithmetic applied to a specific problem. A person on chemotherapy may need energy density prioritized over everything the rest of the book recommends; the reason is that the constraint changed, not that the evidence did.

So this part is not a set of exceptions to Parts I–IV. It is those chapters, evaluated under different constraints — and the skill it teaches is noticing which constraint you're actually under, which is the skill that separates useful advice from a printout.

A note on the two hardest chapters

Chapters 24 and 29 both touch on things people carry a lot of pain about — body weight, and serious illness.

I've written Chapter 24 with the explicit assumption that some readers have been blamed, by clinicians, for a physiological process, and Chapter 29 with the assumption that some readers are reading it in a hospital cafeteria at two in the morning. Both contain ⚠️ callouts pointing to real professional help, and Chapter 24 hands off directly to Chapter 34.

If either one is hard to read right now, skip it. It'll keep.

Start with the athlete who's doing everything right and getting hurt anyway.