Fighting fat: America's new health war

As a nation, almost two-thirds of us-an estimated 97.1 million adults and 6.7 million children and teens-are overweight, says the Centers for Disease Control and prevention. That's more than triple the number just 20 years ago. Why are Americans packing on the pounds? The obvious response: We eat too much. But scientists and health experts think that answer is deceptively simple--and the real question is why we overeat.

Healthy bodies come in all shapes and sizes. But obesity, or extreme excess weight, is linked to around 300,000 U.S. deaths each year as a leading risk factor for killers like heart disease and diabetes, a blood-sugar disorder that can lead to blindness, nerve damage, and organ failure.

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How to deal with what the U.S. Surgeon General calls "the most pressing new health challenge we face today"? Researchers are probing the dizzyingly complex science behind how and why we gain weight. Both genetic (inherited) and environmental factors, like too much food and too little exercise, are under scrutiny-clearly a combination of factors fuels the American weight crisis. Read on to learn how scientists are fighting fat.

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Last year alone the nation shelled out $33 billion on weight loss products from low-calorie foods to diet pills--yet waistlines still expanded. Why? "The truth is, we don't really know," admits obesity researcher Dr. David Cummings at the University of Washington School of Medicine. "But we do have an increasingly better understanding of the body mechanisms that control weight."

According to Cummings, the shape of our bodies, how much we weigh, even how much we're able to eat, may be 50 to 80 percent determined by genes, units of hereditary information stored in our cells. The CDC and National Institutes of Health agree that genes--which control hundreds of weight-regulating compounds in the body, like hormones and brain chemicals--may cause some of us to store more fat, burn fewer calories, and even crave more food. In other words, there's a lot more to fatness than lack of willpower: "We need to remember that for obese people being overweight is not necessarily their fault," says Cummings.

The evidence? Geneticists point to studies on identical twins, siblings born from a single fertilized egg who share a duplicate set of genes. University of Pennsylvania scientists compared the body shapes and weights of identical and fraternal twins, siblings born from separate eggs with similar but not identical genes. The surprising study results: As adults, the identical twins had mirror-image body shapes and weights, even when raised apart. But fraternal twins had body shapes and weights as varied as unrelated individuals, even when growing up in the same home.

How the genes interact in different people--and how much they're influenced by environmental factors, like food and eating habits--is still a mystery. But Cummings and his team are making strides: They recently discovered that a gene called ghrelin (GREY-lynn) plays a starring role in appetite control.

In most healthy people, the ghrelin gene programs stomach cells to produce a powerful hunger-stimulating hormone, a chemical messenger that signals the brain to control body functions. Secreted into the bloodstream, the hormone travels to the brain and activates feeding centers--like the hypothalamus, a forebrain area that regulates food intake (see diagram, p. 18) among other body functions. The ghrelin hormone rises sharply before meals and plummets afterwards: In theory, the more you produce, the hungrier you feel.

Cummings found that dieters who slash calories (see chart, right) have elevated pre-meal ghrelin levels--a condition that may trigger 'overeating. The body literally fights to stay fat, Cummings speculates. The question is, why?

One possible explanation: "For millions of years the human species probably endured common periodic famine," Cummings says. A person whose body slowed down the rate at which it converted food into energy (metabolism) may have been able to fend off starvation. "Today, that's what happens to people who diet--their metabolisms drag," explains Cummings. "It's the body's old attempt to store food for the long haul." He hopes to develop a drug that blocks the ghrelin hormone to help obese individuals shrink their appetites, shed pounds, and keep them off.

THE LIFESTYLE LINK

Genes once advantageous to cave dwellers may be wreaking havoc on modern waistlines. Yet even if genes determine a major portion of our body type and weight, we still have considerable control over our "fat." "The current obesity epidemic doesn't completely reflect genetic factors--but big changes in the way we live our lives," says Dr. William H. Dietz at the CDC.

For the first time in history, we have unlimited access to tasty foods dense with calories (energy units in food) and dietary/'at (energy-rich complex molecules). Our biggest challenge, says Dr. Kelly Brown at the Yale Center for Eating and Weight Disorders: controlling the urge to consume colossal food portions. A single serving of French fries in the 1960s contained 200 calories; today's super-size serving packs about 610 calories (see bar graph, left). At the same time, physical activity is tanking: 26 percent of kids ages 8 to 16 watch four or more hours of TV a day, while participation in gym class has dropped from 46 percent in 1991 to just 29 percent in 1999, according to the U.S. Department of Health and Human Services. "Never has there been a greater need to stress the importance of physical fitness," says HHS Secretary Tommy G. Thompson.