Imagine inviting yourself to dinner with 30 families in 24 different countries to explore humankind's oldest social activity: eating. That's exactly what the husband-and-wife team of Peter Menzel, a photographer, and Faith D'Aluisio, a writer, did. The result was a book called Hungry Planet—a global portrait of the everyday food of everyday people everywhere.

Typical diets around the world have changed rapidly during the past 20 years. In some cases, dietary changes occur when large-scale capitalism reaches new places: When Menzel and D'Aluisio visited China, Kentucky Fried Chicken outlets were springing up all over Beijing.

Other changes are due to rising affluence, as people in formerly impoverished places gain the means to eat more meat and processed foods—and then fast food starts popping up on the menu. The tides of migration bring more changes, as immigrants take their own foods to new lands and acquire new tastes in return.

Menzel and D'Aluisio photographed each family they visited with a week's worth of groceries, and six of the portraits appear here. These photos have much to tell us about how people from different countries, cultures, and levels of society feed their families.

The foods purchased or acquired by each family reflect traditions, of course, but they also demonstrate how diet, nutrition, and health can depend on less controllable matters like poverty, conflict, and globalization.

Humankind's earliest diets were hunted and gathered from the foods that were available as a result of geography and climate. But as soon as people figured out how to trade foods, their diets gained variety.

As the photos show, the diets of most of the world's people today have evolved in response to changes in food production that began in the 1800s with the Industrial Revolution. Modern methods of preservation—like refrigeration or freeze-drying—allow foods to be eaten long after they are harvested. And modern forms of transportation—trains, trucks, and planes—mean that foods can be consumed "fresh" many thousands of miles away.

The photos reflect another phenomenon: Until quite recently, the most serious problem related to food was getting enough to eat. Even today, insufficient food is a fact of life for nearly a billion people. In fact, the world produces more than enough food for everyone: The problem is that it's not distributed evenly.

But as people in developing nations become better off—as hundreds of millions have in recent decades—they change the way they eat. They replace grains and beans with foods obtained from animal sources. They buy more sweets and more processed foods. Soon they eat more food in general. They often become overweight and develop heart disease, diabetes, and other chronic illnesses common in industrialized societies.

Here we have the great irony of modern nutrition: At a time when hundreds of millions don't have enough to eat, hundreds of millions more are eating too much.