The U.N. estimates that more than 10 percent -- some 870 million people -- of the world's population is chronically malnourished. Yet the number of overweight people is even higher -- about 1.4 billion. Over the last 30 years, the global obesity rate has doubled.
To find out why, I traveled to the island of Crete, in southern Greece. I've been reporting around the world for more than 20 years, and I have to admit -- I've had tougher assignments.
I really like Greek food. The fresh vegetables, the olive oil, the herbs, the yogurt, the wine. And lucky me -- since the 1950s, study after study has shown that the Mediterranean diet, and especially the diet of Crete, makes you live longer, protects you from heart disease and cancer, and keeps you from getting too fat. Look at lists of the world's healthiest diets, and the one from Crete often ranks at the top.
Unfortunately, hardly anybody follows it anymore.
I met a 16-year-old I'll call Eleni with her mother in Chania, a port city of about 50,000 in western Crete. Eleni's grandparents lived in the countryside, but she and her parents grew up in town. Her favorite musician is Justin Bieber. Her favorite foods are hamburgers and pizza.
Eleni has struggled with her weight most of her life. She's been up to about 200 pounds. Schoolmates have taunted her. Her mother told me she tries to lose weight, but then she lapses.
"Sometime she eats a lot," she said. "And she eats everything. Whatever you can imagine. But other times she's okay. I don't know. That's the problem."
She thinks her daughter's weight issues have to do with lack of discipline and low self-esteem. But clearly there's something bigger going on. Today Greece has the one of the highest obesity rates in the world. The proportion of overweight children -- about 40 percent -- may be the highest, except for some Pacific islands. The problem's especially bad in Crete, home to what could be the world's healthiest diet. So what gives?
"It has to do with many factors," said Christina Makratzaki, a local dietitian who also battled obesity as a teenager. We met at a waterfront café full of European tourists.
"In the '50s and '60s, the people, they were poor, but they were healthy," she explained. "They were eating very good foods -- the olive oil, the olives, the green leafy vegetables that are our treasure. But they were enforced in a way because of their poverty to use these things."
Then people here got a little money -- from tourism, from agriculture -- and everything changed.
"Now, we have many choices," she said.
Like processed food from the supermarket and fast food on the street. And soda and doughnuts and ice cream. All of it cheaper to buy, easier to prepare -- and, especially for children, harder to resist -- than what grandma used to make. And then there's the marketing -- a relentless bombardment of ads aimed at kids for products like soft drinks and breakfast cereal and processed meat.
Before I left for Crete I spoke with Marion Nestle, a nutritionist at New York University whose books include "What to Eat" and "Why Calories Count." "World trade has opened up a world marketplace in food that's like nothing the world had never seen before," she said. She told me nearly every society is going through what Crete has gone through -- even in places where hunger is still endemic. It's known as "the nutrition transition."
"The nutrition transition happens very quickly," she said. "As soon as people get money, they start buying more meat and more processed foods. Well, that's fine if you don't eat too much of it. The problem is that we as humans, when we're confronted with large amounts of delicious food, we eat large amounts of food."
There is some disagreement among nutrition experts on the exact causes of obesity. Nestle believes it is mainly a question of "calories in and calories out" -- if we eat too much and exercise too little, we're bound to get fat. Others think the types of things we eat matter more than the amount; for instance, simple carbohydrates encourage us to eat more and retain more fat than other foods. (The traditional Cretan diet is high in fat, mostly from olive oil, yet people who adhere to it rarely became obese.) Some recent research suggests that changes in our intestinal bacteria may play an important role.
The word "diet" actually comes from the Greek -- it originally meant "way of life." And clearly obesity has to do with more than just what people eat.
It typically starts with the upper classes, who do less physical work and can afford to buy more fattening food. For a while, being plump is a sign of wealth and health. But then, in most places, there's a shift. People with money start to value thinness. At the same time, farmers move into the cities, women join the work force and have less time to cook, machines replace manual labor, kids watch more TV and packaged food becomes cheaper than fresh food. Pretty soon you have an epidemic, with the worst effects felt among those with lower incomes.
"Health officials and policy makers are realizing what the costs of obesity are likely to be not only to the individuals themselves but to the society," Nestle said. "The question is what to do about it. People are trying lots of different things, and more power to them. But nobody really has an answer."
The dietitian Christina Makratzaki showed me some of the things people are trying in Crete. A burger chain has started serving things like freshly squeezed juice and turkey wraps. The canteen at the local bus station is offering traditional Cretan dishes, bathed in olive oil. The association of school snack bar operators has told its members to cut out the sweets and sodas at the kiosks they rent, and most have complied.
But all those things are voluntary. To find out what the government's up to, Makratzaki and I dropped in on the mayor of Chania, Emmanouil Skoulakis. He is a doctor who served several terms as Greece's deputy minister of health.
It had been a rough week. On the day we met, the city's workers were on strike. The day before that it was the teachers. Skoulakis said the obesity crisis was of great personal interest to him -- that was why he was willing to see me.
He told me the city sponsors exercise programs and a local food festival, where people could talk with chefs and sample traditional cuisine. Last spring, it helped organize visits by 14 dietitians to some of the schools. But money is tight. Beyond rallying volunteers, he said, there's not much the government can do.
That's especially true now, with Greece in crisis. Unemployment is 25 percent and people are marching in the streets. I asked everyone I met if they thought the economic troubles may have a silver lining, sending people back to the old ways, eating fruits and vegetables and dessert just on Sundays. They all shook their heads. With junk food so much cheaper than fresh food, they say, the lighter people's wallets, the heavier they'll get.