In March 2023, Japanese medical authorities announced that the new drug—which was in staggering demand across the world, causing shortages—had been approved to treat obesity in their country. It sounded, at first glance, like great news for Novo Nordisk, the company that makes Ozempic and Wegovy. But industry outlet the Pharma Letter reported that this would not in fact turn out to be much of a boost. They predicted that these drugs would dominate the market in Japan, but that won’t mean much, for a simple reason: there is almost no obesity there. Some 42% of Americans are obese, compared with just 3% of Japanese people. Japan, it seems, is the land that doesn’t need Ozempic.

I wondered how this could be, and if the answer might offer me a way out of a dilemma that was obsessing me. Several months before, I had started taking Ozempic, and I was traveling all over the world to interview the leading experts on these drugs to research my new book, The Land That Doesn’t Need Ozempic. The more I discovered, the more torn I became. I had learned there are massive health benefits to reversing obesity with these drugs: for example, Novo Nordisk found that weekly injections reduced the risk of heart attack or stroke by 20% for participants with a BMI over 27 and a history of cardiac events. But I also saw there are significant risks. I interviewed prestigious French scientists who worry the drugs could cause an increase in thyroid cancer, and American experts who worry it will cause a rise in this problem. Other experts fear it could cause pancreatitis or cancer. These claims are all fiercely disputed and debated. I felt trapped between two risky choices—ongoing obesity, or drugs with lots of unknowns.

So I went to Japan, to discover: how did they avoid this trap? My first assumption was that the Japanese must have won the genetic lottery—there had to be something in their DNA that makes them stay so slim. But in the late 19th and early 20th century, large numbers of Japanese workers migrated to Hawaii and they have now been living on the island for four generations. They are genetically very similar to the Japanese people who didn’t leave. It turns out that after 100 or so years, Japanese Hawaiians are now almost as overweight as the people they live among. Some 24% of them are obese, compared to 24.5% of Hawaiians overall. That means Japanese Hawaiians are four times more likely to be obese than people back in Japan. So something other than genes explains Japan’s slimness. But what?

I glimpsed part of the explanation when I went to the Tokyo College of Sushi & Washoku, to interview the president Masaru Watanabe, who I also spoke with on Zoom on another occasion. He had agreed to cook a meal for me with some of his trainees, and to explain the principles behind it. He told me: “The Japanese cuisine’s [core] feature is simplicity. For us, the simpler, the better.”

He began to make a typical Japanese meal, the kind people were eating all over the country that lunchtime. He and his chefs grilled a mackerel, boiled some rice, made some miso soup, and prepared some pickles. “We don’t traditionally eat meat a lot. We are an island country. We appreciate fish.” As the mackerel was grilled, I watched as various oils and fats leeched out. Even more importantly, Masaru explained, this was an illustration of one of the crucial principles of Japanese cooking. Western cooking, he said, is primarily about “adding.” To make food tasty, you add butter, lemon, herbs, sauces, all sorts of chemicals. “But the Japanese style is totally the opposite.” It’s “a minus cuisine.” It is about drawing out the innate flavor, “not to add anything extra,” he said. The whole point is to try “to make as much as possible of the ingredients’ natural taste.” To Japanese cooks, less is more.

He also said Japanese meals have very small portions, but more of them—five in a typical meal. Before we started to eat, Masaru explained the Japanese principles of eating. The first thing I had to learn was “triangle eating.” All my life, when I was eating a meal with different components, I would mostly eat them sequentially—start the soup, finish the soup; start the salad, finish the salad; start the pasta, finish the pasta. “In Japan, this is regarded as really weird,” he said. “It’s a rude way of eating.” A meal like this should be eaten in a triangle shape. “First, drink the soup a little bit, then go to the side dish—one bite. Then try the rice, for one bite. Then the mackerel—again, a single mouthful. Then go back and have another taste of the soup,” he said. “This is also the key to keep you healthy … Keeping the balance, so you don’t eat too much.”

The second thing we had to learn is when to stop. In Japan, you are taught from a very early age to only eat until you feel you are satisfied. It takes time for your body to sense you’ve had enough, and if you hit a sense of fullness while you are still eating, then you’ve definitely had too much.

I ate nothing but Japanese food like this on my trip, and three days in, I began to experience an odd mixture of hope and humiliation. I felt healthier and lighter, but I also thought—the Japanese people have built up a totally different relationship to food over thousands of years, in ways we can’t possibly import. So I was surprised to learn that most of Japan’s food culture was invented very recently—in living memory, in fact. Barak Kushner, who is professor of East Asian History at the University of Cambridge, told the writer Bee Wilson, for her book Consider the Fork, that until the 1920s, Japanese cooking was just “not very good.” Fresh fish was eaten only once a week, the diet was dangerously low in protein, and stewing or stir-frying were not much of a thing. Life expectancy was a mere 43. It was only when Imperial Japan was creating an army to attack other parts of Asia that a new cuisine began to be invented, quite consciously, to produce healthier soldiers. After the defeat of Japan in the Second World War, when the country was in ruins, the new democratic government stepped up this transformation.

To find out how Japan created a radically different food culture, I arrived at Koenji Gakuen School with my translator on a stiflingly hot September morning. It’s a typical school for kids aged from five to 18 in a middle-class neighborhood in Tokyo. We were greeted near the entrance by Harumi Tatebe, a woman in her early 50s, who had been the nutritionist there for three years. As we walked through the corridors, kids waved at her affectionately, and shouted her name, eager to know what they were having for lunch that day. By law, Harumi said, every Japanese school has to employ a professional like her. It took her three years to qualify, on top of her teaching degree, and she explained that in this position, you have several important roles to play. You design the school meals, in line with strict rules stipulating that they must be fresh and healthy. You oversee the cooking of the meals. You then use these meals to educate the children about nutrition. Then you educate their parents on the same topic.

Harumi told me that today’s meal consisted of five small portions: some white fish, a bowl of noodles with vegetables, milk, some sticky white rice, and a tiny dollop of sweet paste. All the kids eat the same meal, and packed lunches are forbidden. No processed or frozen food ever goes into any of the meals here. “We start from scratch,” she said. “It’s all about nutrition … Sometimes with frozen food, they use a lot of artificial additives.”

Once the meal was ready, Harumi carried a tray over to the office of the school’s head, Minoru Tanaka. It is a legal requirement that the principal of each school ensures lunches meet nutritional guidelines. It’s also customary for principals to have the same lunch as the kids and to eat it first, to make sure it’s safe, nutritious, and delicious. He rolled up his sleeves and dug in. Before they began to eat, a child stood at the front of the class and read out what today’s meal was, which part of Japan it came from, and how the different elements are good for your health. She then