That's the conclusion of a 15-year study of white and black Americans that was presented at a just-concluded conference of the American Heart Association.
White people who watch 2.5 hours of TV every day and eat fast food twice a week have nearly three times the risk of becoming obese and developing high blood sugar, which are strong risk factors for heart disease and Type 2 diabetes, the study found.
Even the average white person, who watches two hours of TV a day and eats fast food once or twice a week, has double the risk they should, says study co-author Mark Pereira, an assistant professor of pediatrics at Harvard University School of Medicine.
Curiously, the study found fast food did not have the same effect on black people.
"Fast food consumption in this country has increased dramatically," says Pereira.
He blames the rise, which mirrors growing obesity in the United States, largely on advertising and the sedentary lifestyle that accompanies TV viewing.
"It's a question of energy expenditure, but we're realizing that it's also a question of exposure to marketing strategies," Pereira says. "There's no question that it influences behavior."
The study followed 2,027 white and 1,726 black adults between the ages of 18 and 30 for 15 years, tracking their lifestyles, diets and health through physical examinations.
For whites, the study found a strong association between TV watching, fast food and health risks associated with heart disease and Type 2 diabetes.
However, the results were more puzzling for blacks.
The researchers couldn't link fast food consumption in blacks to increased risk of obesity and high blood sugar. The disparity may result from different dietary patterns that weren't addressed in the study's interviews, but it may also indicate a striking difference in responses to fatty foods, Pereira says.
"We think this is the first study that has shown this. So, it needs more examination," he says.
While fast food may not be tied to obesity for blacks, excessive TV watching has been linked to obesity, says Carlos Crespo, an associate professor of social and preventive medicine at the University of Buffalo in New York.
"Television is very powerful," Crespo says, noting that 60 percent of TV advertising is for food products.
In a study of 4,000 children completed two years ago, Crespo showed that black and white children both take in more calories the more they watch TV. Kids who watch four hours of TV a day eat about 150 calories more than those who watch two hours.
Americans are eating more and exercising less, he adds. However, what alarms Crespo most is that many adults think exercise alone will help them avoid obesity, without also watching their diets. Even if a person burns 300 calories during 30 minutes of exercise, they take in nearly twice that with each order of French fries, Crespo says.
Still, exercise helps keep weight off, even if it doesn't slim you down. Moreover, studies have show the risk of heart disease, especially for obese Americans, drops with exercise, he says.
"Over 50 percent of Americans are overweight," Crespo says. "We've got a big problem here. In 20 or 25 years, that bomb is going to explode in our hands. It's a major public health priority, and it's just getting worse and worse."
To learn more about obesity trends in the United States, visit the U.S. Centers for Disease Control and Prevention. For suggestions on preventing and treating obesity in children, visit this site by the Office of the Surgeon General.