"Chronic, incurable, and unpredictable." That is what the neurologist said in 2002, when he showed Jolien Janzing the white spots on her scan and told her she had multiple sclerosis. She has been symptom-free for many, many years.

This is the book about what she changed.

Janzing is an investigative journalist and a novelist, not a doctor. When she asked her neurologist whether there was anything she could do herself — follow a diet, perhaps — he shrugged. "Eating healthy is good, of course, but you shouldn't overdo it." So she went to the research herself, the way she had researched every other story of her working life.

What she found was a mismatch. Human beings lived as hunter-gatherers for some 300,000 years. Farming arrived around 10,000 years ago, and the ultra-processed food that fills our supermarkets is younger still. Our genes never got the message. Chronic inflammation, autoimmune disease, insulin resistance and weight that will not shift are part of what that gap costs us.

Step by step, she went back to eating the way her body was built to eat. She calls her illness a fire-breathing dragon and her food the sleeping potion. The dragon has stayed asleep.

Inside this book:

• The Oldest Diet in full — what you can eat freely, what to leave on the shelf, and the reasoning behind every choice
• A seven-day meal plan, and recipes for the meals she cooks every day
• How to begin without upending your kitchen, your budget or your family
• What the evidence shows on inflammation, autoimmune disease, insulin resistance, gut health, bones, the brain and ageing — fully referenced, so you can check it yourself
• A section on the pioneers she learned from, among them Loren Cordain, Terry Wahls, Mark Hyman, Jason Fung and David Perlmutter
• Eating out, packed lunches, fasting, supplements, sleep and movement

Whether you are living with a chronic illness, carrying weight that will not go, or simply intending to grow old without falling apart, the principle is the same: your body is built to run on the food your ancestors ate.

In 2002 Jolien Janzing was told to wait and see what the disease would do to her.

She did not wait. You do not have to either.