Introduction

You are, in a fairly literal sense, made of things that used to be somewhere else. The carbon in your muscle was in the air a few years ago. The calcium in your bones was in rock, then in soil, then in a plant, then in a cow, then in a glass. The iron carrying oxygen around your body right now was in the ground before it was in a lentil. Every atom of you crossed a boundary to get there, and almost all of it crossed through your mouth.

That boundary is the subject of this book. What crosses it, where it came from, what it does once it is inside, and what you actually need to know to make decent decisions about it.

Three kinds of thing cross that boundary

Food, which is mostly plants and animals, arrives as an enormously complicated mixture. An apple is not "sugar and fibre and vitamin C." It is several thousand distinct compounds, most of them present in tiny amounts, most of them never studied, some of them made by the tree specifically to discourage things from eating it. Your body takes that mixture apart, uses some of it, ignores a great deal of it, and hands a large fraction of the rest to thirty-odd trillion bacteria living in your colon who have their own opinions about what to do with it.

Medicine arrives as the opposite: one molecule, purified to within a fraction of a percent, at a dose worked out in clinical trials, in a tablet engineered to dissolve at a particular speed in a particular part of your gut. Medicine is precise in a way food never is. That precision is exactly why it works and exactly why it can hurt you.

Everything else arrives without asking. Caffeine and alcohol and nicotine, which are drugs we have agreed not to call drugs. The additives that keep bread soft and sausage pink. The compounds that did not exist in the raw ingredients and got created by the pan. Lead in old pipes, arsenic in rice paddies, mercury in big fish, cadmium in cocoa. Plastic and non-stick coating and whatever is in the air of a kitchen with the gas on and the window shut.

Most books handle one of these three and pretend the other two are somebody else's department. That is a mistake, because your liver does not know the difference. The same enzyme system that breaks down a painkiller also breaks down a compound in grapefruit, which is why the two together can be dangerous. The same transporter that absorbs iron from spinach also absorbs lead from a water pipe. The body has one set of doors, and everything comes through them.

What this book actually contains

The farming. This book starts in the soil, and it does not rush. If you want to understand why a supermarket apple is picked hard in September and sold to you in July, why the entire world's banana trade runs on a single sterile clone that cannot breed, why some crops need a cold winter and others die in one, or why "organic" does not mean "no pesticides," you need to understand how a farm works. So there are nine chapters on that first: what a plant is doing when it makes fruit, what soil is made of, how climate and water and chill hours decide what will grow where, what happens across a farming year, how varieties are bred and grafted, what gets sprayed and why, what the labels mean, and how produce survives the trip to you.

The produce, crop by crop. Then the aisle itself. Apples get a full chapter, because the reader who prompted this book asked for one and because the apple turns out to be a remarkably good teacher: it is a clone, a cold-storage marvel, a fibre delivery system, and a case study in why "an apple a day" has both more and less behind it than people think. Then bananas, citrus, berries, grapes, stone fruit, melons, mango and papaya, pineapple and kiwi, avocado, tomato, pear, pomegranate, figs and dates, the tropicals most people have never bought, olives and coconut, and the marketing category called superfruit. Then vegetables: the greens, the brassicas, the onion family, the roots, potatoes, the cassava and sweet potato staples that feed a billion people, squashes, chillies, legumes, mushrooms, seaweed, and the herbs and spices that are, chemically, the most concentrated plant material you will ever eat. Then grains, nuts, oils, dairy, meat, fish, fermented food, salt and sugar, and the honest chapter about ultra-processed food.

The digestion. Between the growing and the eating sits a section on what actually happens after you swallow. The journey of one bite from mouth to toilet with timings. Blood sugar and why the same gram of sugar behaves differently depending on what it arrived with. Protein, fat, fibre, and the microbiome. Every vitamin and every mineral, what each one does, what happens when you run short, and which ones people actually run short of. The plant chemicals with health claims attached, sorted into what is established and what is a press release. The natural toxins genuinely present in ordinary food. And whether the time of day you eat matters, which has a more interesting answer than either camp admits.

The medicine cabinet. Then drugs, on the same fixed template. What a drug even is: absorption, distribution, metabolism, excretion, half-life, receptors, dose-response. How a drug gets discovered, tested, approved, and physically manufactured, including what is actually in a tablet besides the drug. How to read a package insert. Then the drugs themselves: paracetamol, ibuprofen and the NSAID family, aspirin, opioids, cold and flu combinations, antihistamines, stomach drugs, antibiotics, antivirals, vaccines, blood pressure and cholesterol drugs, diabetes and weight drugs, antidepressants and the rest of the psychiatric cabinet, inhalers, hormones, and supplements. Then the situations that change all the rules: children, pregnancy, old age, interactions, and how to tell a real side effect from a coincidence.

The chemicals. Finally the things that are neither food nor medicine. Caffeine, which is the world's most used psychoactive drug by an enormous margin. Alcohol. Nicotine. Food additives and what the E numbers mean. What cooking creates that was not there before. Heavy metals and where they actually come from. Plastics, PFAS, packaging, and cookware. The air indoors. And a chapter on toxicology from scratch, because "the dose makes the poison" is the single most useful sentence in this entire subject and almost nobody applies it consistently.

What this book will not do

It will not tell you that any single food is magic. No fruit cures anything. The strongest, most repeatedly confirmed findings in nutrition are boring: eat more plants, eat more fibre, eat less ultra-processed food, drink less alcohol, do not smoke. Every exciting claim beyond that is weaker than its headline.

It will not pretend the evidence is stronger than it is. Nutrition science is hard. You cannot randomise ten thousand people to eat blueberries for thirty years. Most of what we know comes from observational studies, which can tell you that blueberry eaters are healthier and cannot tell you that blueberries made them so. When a claim rests on a mouse study or a test tube, this book says so.

It will not give you medical advice. Doses appear in these pages because you cannot explain a drug without them, and they are illustrative. Real dosing depends on your weight, your kidneys, your liver, your other medicines, your pregnancy status, and your age. Use this book to understand what your pharmacist and doctor are doing, and to ask better questions. Do not use it to overrule them.

It will not moralise about food. There is no clean and unclean here, no detox, no superfood, no foods that "flush toxins." Your liver and kidneys do that, continuously, and they do not need help from celery juice.

Who this is for

Anyone who has stood in a supermarket wondering whether the expensive tomatoes are different, whether frozen peas are worse than fresh, whether that apple has been in storage since last autumn, and what exactly the wax on the skin is. Anyone who has looked at a pill and wondered what the other 90 percent of the tablet is. Anyone who has been told to take ibuprofen with food and wanted to know why, or whether it is even true. Anyone who read a headline about a chemical in their pan and could not tell whether to panic.

No background is assumed. Not chemistry, not biology, not farming. Every term is defined the first time it appears, every mechanism is explained rather than named, and where a number matters it is given rather than gestured at.

Start with How to read this book, which explains the twelve-part template that most chapters follow and, more importantly, the safety rules.

👉 On to how to read this book.