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.
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.
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.
Many studies show physically fit people are less likely to develop a host of diseases from diabetes to depression–regardless of body type. “We’re far too hung up on weight,” says obesity specialist Dr. C. Wayne Callaway at George Washington University. “I’d much rather see a heavy person who’s physically active than a skinny person who’s out of shape.”
Still, the U.S. Surgeon General urges Americans to shed extra pounds. “Most people can control up to 10 percent of their body weight,” Cummings says. “Losing 30 pounds won’t make a very heavy person look svelte, but it promotes incredibly positive health benefits.”
Why some people pack weight on more easily than others remains a puzzle, but in terms of obesity research, there’s light at the end of the tunnel. “In the next decade we’ll be able to manage weight problems with medications much as we now manage other illnesses,” says Cummings.
Doctors use the Body Mass Index (BMI) to help determine if a person is overweight. To calculate BMI, divide your weight (in pounds) by your height (in inches squared). Then multiply the results by 704.5. The National Institutes of Health generally defines overweight as a BMI of 25 to 29.9 and obesity as a BMI of 30 or greater. For more on BMI, see the Teacher’s Edition.
THE ENDOCRINE SYSTEM: HOW IT REGULATES WEIGHT CONTROL
A complex network of glands (cell clusters) called the endocrine system works 24 hours a day to regulate body weight, it coordinates the release of hundreds of hormones, or chemical messengers, into your bloodstream. Hormones help control when and how often you feel hungry, how much you eat–even how quickly food is burned as energy. They also regulate sleep, breathing, growth, and emotions.
HORMONES AND OBESITY
Two hormones, leptin and ghrelin, play an important role in obesity.
Leptin is secreted into the bloodstream by fat cells found in the stomach. Leptin signals the brain’s hypothalamus to secrete hormones that suppress hunger.
Ghrelin is secreted into the bloodstream by stomach glands. It signals the hypothalamus to secrete hunger-stimulating hormones.
When people diet, ghrelin levels rise and leptin levels fall. Appetite increases, making it harder to lose weight.
WEIGHT PATROL: KEY PLAYERS OF THE ENDOCRINE SYSTEM
Controls at least 40 neurotransmitters (brain chemicals) that regulate eating. Food releases the “pleasure-causing” chemicals dopamine and serotonin in the brain.
This pea-size “master gland” secretes hormones that control most of the other endocrine glands.
A brain region that fields and interprets eating cues from glands scattered throughout the body.
Secretes thyroxine, a hormone that speeds up the rate at which your body cells burn energy (metabolism).
TOO MUCH OF A TASTY THING?
AMERICANS spend 30 percent of their food dollars on fast food, says the U.S. Department of Agriculture. Food-on-the-go is often rich in fat and calories.
THE BIOLOGY OF HUNGER
SLIM GENES The leptin gene is thought to produce a hormone that curbs appetite in both humans and mice. The mouse on the left is more than three times its normal weight, because it was born with a faulty leptin gene.
COULD THE STOMACH hormone ghrelin trigger our desire to eat? Scientists found that ghrelin levels rise sharply before meals, especially in dieters, but remain low after a drastic weight-loss surgery that reroutes food past the stomach to the intestines. Singer Carnie Wilson has kept off 15D lbs. since her gastric bypass surgery in 1999.
AN ESTIMATED 13 percent of U.S. teens ere overweight. That’s more then double the percentage in 197D, according to the CDC. One possible culprit: giant portion sizes. This bar graph compares portion sizes and calories of three common junk food items from 1955 and 2000. By whet percentage is a 20 oz soda larger than a 6.5 oz soda?
1995 2.3 oz 210 calories
2000 6.9 oz 610 calories
1995 6.5 oz 80 calories
2000 20 oz bottle 250 calories
1995 1.1 oz 150 calories
2000 3.7 oz 510 calories
Note: Table made from bar graph.
Did You Know?
* What you eat even as a newborn may hardwire your body to store more fat cells as an adult, according to University of Buffalo researchers. Scientists fed newborn rats milk formula 49 percent higher in carbohydrates than the milk rats normally suckle. Within the first 24 hours of feeding, the pups had abnormally high levels of insulin, a hormone that triggers cells to absorb sugar. (Sugar in the blood not used for energy is stored in the body as fat.) Two months later the rats began gaining weight, and became obese in adulthood–even in the absence of a carbo-rich diet.
* According to the U.S. Surgeon General, some overweight kids may need only focus on maintaining their current weight while growing normally in height.
Social Studies: Study the history of fast food and how it changed America’s eating habits. Be sure to compare restaurant menus from the early years to the offerings today. How are they different in selections and serving sizes?
Critical Thinking: How have today’s media outlets skewed the perception of healthy body shapes?
“Fat for Life?” by Sharon Begley, Newsweek, July 3, 2000
The Surgeon General’s Call To Action To Prevent and Decrease Overweight and Obesity: www.surgeongeneral.gov/topics/obesity/calltoaction/fact_adolescents.htm
CHECK FOR UNDERSTANDING
Directions: Answer the following in complete sentences.
1. What do doctors use to help determine if a person is overweight?
2. What body system regulates weight control?
3. In a comparison of food portion sizes between 1955 and 2000, what is the most significant difference?
4. What factor may determine 50 to 80 percent of our body shape, size, and how much we’re able to eat?
5. According to numerous studies, what health risks are less prevalent in physically fit people?
1. Doctors use the Body-Mass Index to determine if a person is overweight.
2. The endocrine system regulates weight control.
3. The food portion sizes in 2000 are significantly larger than the portion sizes in 1955.
4. Our shape, size, and how much we’re able to eat may be 50 to 80 percent determined by genes.
5. Studies show that physically fit people are less likely to develop a host of diseases from diabetes to depression.
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