June 7, 2004
All these customs are more than cultural frippery, though we don't always realize it until food and tradition come uncoupled. Among immigrants, particularly those coming to the U.S., the obesity problem has become a full-blown crisis. Even the stubbornest new arrivals may find that their food practices are impossible to maintain in a new environment, where familiar ingredients aren't available, old-world holidays aren't observed and the Mediterranean tradition of the heavy lunch must yield to the less healthy practice of postponing the big meal until the end of the day. "There's a lot of food-related culture shock for new immigrants," says anthropologist David Himmelgreen of the University of South Florida in Tampa.

That discordance can do a lot of damage. Himmelgreen tracked the weight of Puerto Rican women living in the continental U.S. and found that the longer they had been here and the better their English, the more they tended to weigh. "People's food habits change dramatically when they arrive," he says. "The weight gain can happen in a very short time."

For people who have always lived in the U.S., the problem is even worse. There are a lot of reasons for America's obesity epidemic—oversize portions, overprocessed foods, too little exercise. But nutritionists and anthropologists agree that the death of the official mealtime may play the biggest role. "By the time children go to middle school," says anthropologist Marquisa LaVelle of the University of Rhode Island in Kingston, "many families have basically stopped eating together." Solitary eating can be uncontrolled eating—snacks, sweets and meals behind the wheel. "By age 10, everyone in the family can feed themselves whatever they want—and they do," says LaVelle.

Families can change all that. Picking better foods and preparing them healthfully certainly helps. But so does a return to the time when eating was seen not just as a way to fill up but as an opportunity to transact the business of being human. A set table and a balanced meal take a lot more work than a carry-out pizza. But the rewards are infinitely richer.

FOR BIOLOGICAL REASONS
Our desire for food—and lots of it—is hardwired into our cells. Do our bodies want to be fat?

There's no question that some pretty strong social, emotional and behavioral forces play a part in determining what, when and how much we eat. But if you really want to know why some people are fat and others aren't, you have to take a good look at biology as well. Mother Nature simply can't afford to leave anything so important to human survival as eating to the whims of cultural fashion. Ten years after the discovery of the first obesity gene, scientists are only beginning to understand just how hardwired our desire for food—and lots of it—truly is.

What they are finding is an exquisitely fine-tuned system of chemical and neurological checks and balances that regulates both what we eat and how much our bodies store as fat. The average American consumes about 1 million calories a year—and, under normal circumstances, burns almost exactly that amount. The body achieves that balance by automatically increasing or decreasing the efficiency with which it performs various tasks, thus consuming fewer or more calories. (Most of the calories we expend are used to breathe, maintain body temperature, keep the brain chugging along, etc. Depending on how much you move, physical activity typically accounts for 15% to 30% of the total.) If you pack on a couple of pounds over the course of the year, your body's error rate is still less than 1%.

Accomplishing that feat requires a lot of communication and coordination among the fat cells, the liver, the muscles, the brain, the stomach and the gastrointestinal tract. Sometimes the signal is a molecule. Other signals are actually conducted along nerve paths. There are even mechanical signals, like the stretching of the stomach, which is one way the body says, "I'm full."

As if all that weren't complicated enough, the body must also regulate its food intake and manage its weight over time. "There are short-term signals and long-term signals," says Judith Korner, an endocrinologist at Columbia University in New York City. "Some signals are both short term and long term, and then there are medium-term signals."

As you might expect, the short-term signals are involved mostly with the initiation and completion of meals. Ghrelin, a hormone produced by the stomach, tells the brain, "It's time to eat!" When enough food leaves the stomach and reaches the small intestine, another hormone, called cholecystokinin, signals that the meal is over—and triggers the release of enzymes in the gallbladder and the pancreas.

The hormones leptin and insulin are longer-term signals. Produced by fat cells, leptin helps manage just how much fat you store around your organs and under your skin through a complex feedback loop. If your fat deposits start to shrink—for example, when you lose weight—the amount of leptin in your body falls, a situation that the brain interprets as a result of starvation. The whole system of chemicals and neurological impulses shifts in an attempt to get the body to burn fewer calories so that it can regain the weight. The greater the weight loss, the stronger the signals to eat more and replenish fat stores.

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