Part I — Foundations

Chapters 1–6

There is a question I get asked more than any other, usually in the last two minutes of an appointment, usually while the person is already standing up with their coat half on.

"Okay, but just tell me — what should I eat?"

It is a completely reasonable question and I am going to refuse to answer it for the next six chapters.

Not because I'm being coy. Because if I answer it now, you'll have one more voice in the pile. You already have a pile. You have the cardiologist and the neighbor and the algorithm and the man on your feed with the tank top and the cortisol theory, and adding a dietitian with a doctorate to that pile does not reduce your confusion by very much. It just makes the pile taller.

What actually helps is the thing underneath the answer: why the pile exists, and how to sort it.

What this part does

Part I is about learning to think before learning what to eat. Six chapters:

Chapter 1 diagnoses the chaos. Why is nutrition specifically so much worse than other health fields? Part of it is that studying diet in free-living humans is genuinely, structurally hard — harder than studying drugs, harder than studying surgery. Part of it is that the incentives of everyone who talks to you about food, in both directions, are misaligned with your health. And part of it is a pipeline that turns a modest finding into a confident reel in about four steps, each of which is individually defensible and collectively catastrophic. You'll meet Theo, who has tried five diets and concluded the problem is him, and Coach Brandt, who has two million followers and is sincerely trying to help.

Chapter 2 is the most important chapter in this book. 🚪 It hands you the evidence ladder, healthy-user bias, confounding, reverse causation, relative versus absolute risk, and the question that unlocks every nutrition argument you will ever have: compared to what, in whom, for how long? Every chapter after this one draws on it. If you read one chapter of this book in your life, read that one.

Chapter 3 is the plumbing. Mouth to bloodstream: what actually happens to a sandwich. This is the chapter that makes fiber, the microbiome, food intolerances, and clinical nutrition comprehensible later, and it quietly kills a surprising number of myths on its own — you cannot believe in most detoxes once you understand what a liver does.

Chapter 4 🚪 takes the loudest fight in nutrition — "a calorie is a calorie" versus "calories don't matter" — and shows that both camps are defending something true and attacking something nobody said. Energy balance is thermodynamically non-negotiable and nearly useless as practical advice, and holding both of those at once is a gateway that a startling number of professionals never walk through.

Chapter 5 🚪 does the arithmetic. Resting metabolic rate, the thermic effect of food, activity, NEAT, and the total — worked step by step on a real person, with honest error bars, because an equation that's ±10% at best gets quoted to four significant figures by every app you've ever installed. It also addresses the sentence I hear weekly: "I think my metabolism is broken." It isn't. Something else is happening, and it's more interesting.

Chapter 6 ★ 🚪 goes one level down, into the cell, and does it without requiring a chemistry background. Glycolysis, beta-oxidation, gluconeogenesis, ketosis, mTOR — the actual machinery behind every "fat-burning zone" and "metabolic switch" claim you've been sold. It exists because you cannot properly evaluate the keto argument, the fasting argument, or the protein argument without knowing roughly what's happening in there.

A promise about the difficulty

Part I is the most conceptually demanding section of the book, and it front-loads the work deliberately.

Chapter 2 will ask you to think about study design, which sounds like the least appetizing possible topic for a book about food. Chapter 6 will show you metabolic pathways, which is the part of nutrition coursework students most often describe as the moment they stopped enjoying it.

I've written both with the assumption that you have no background at all, and with a hard rule: no mechanism goes on the page without an analogy, and no equation goes on the page without every step of the arithmetic shown. If either chapter loses you, that's a defect in my writing, and there's a 🏃 Fast Track note at the top of each telling you exactly what you can skim and still be fine.

But I'd rather you found Part I a little hard than found the rest of the book easy and empty. Everything after this — the macronutrient chapters, the myth chapters, the fights about seed oils and sugar and fasting — only works if you can evaluate a claim yourself. Otherwise I'm just another voice on the pile, and you have enough of those.

What you'll be able to do at the end of Part I

  • Explain to someone why nutrition headlines contradict each other, without shrugging
  • Place any study on an eight-rung ladder and know what it can and cannot tell you
  • Spot healthy-user bias, confounding, and reverse causation in a claim
  • Convert "X causes Y" into "X compared to what, in whom, for how long?"
  • Describe what happens to food from mouth to bloodstream
  • Hold both halves of energy balance at once without collapsing into either camp
  • Calculate your own energy requirements and state the honest uncertainty in the number
  • Explain, at a useful level, what your cells do with carbohydrate, fat, and protein

And you'll have started your own Nutrition Framework: a belief inventory, a claim filter, a digestion log, a three-day food diary, your own energy numbers, and a fuel-mix reflection. Six components down, thirty-two to go.

Let's start with why nobody agrees.

Chapters in This Part