Karen Collins, MS, RD, CDN
American Institute for Cancer Research
In identifying the factors most closely linked to overweight, the American Institute for Cancer Research (AICR) 2007 report on diet, physical activity and cancer prevention advises the public to be physically active. The report also specifically recommends limiting sedentary habits such as watching television. Now, more recent studies add to emerging evidence that TV’s impact on weight may be substantial.
A negative impact from television time is seen in children as young as 2 to 5 years old. In a large national survey, higher weight was 34 percent more common among those children who watched more than two hours of television daily. In adolescence, the association remains strong for girls, while the link between TV and overweight becomes less consistent for adolescent boys.
By adulthood, the link is again consistent for both genders. In a study of 26 to 36-year-olds, those watching more than three hours of TV daily were more likely to have excess waist fat than those watching an hour or less. Elsewhere, middle-aged adults who watched more than four hours of TV daily showed waists averaging over an inch larger than those watching less than two hours daily; their percent body fat and body mass index were also higher.
It’s easy to assume that the television-overweight link occurs when TV replaces physical activity. For many people, this does hold true. But even when TV doesn’t displace physical activity, research shows that we move around less and burn fewer calories when watching TV than when participating in other sedentary activities like playing board games, writing, reading or sewing.
Indeed, studies repeatedly find that the amount of time people are physically active and the amount of time they spend watching TV affect body weight independently of each other. In one study of Australian adults, spending a lot of time in sedentary behaviors increased the odds of being overweight or obese by more than 50 percent, even among participants who got the recommended amounts of physical activity. Lots of sedentary time and too little time being physically active more than doubled the odds.
Television also seems to impact weight by affecting our eating habits. Dinner in front of the TV is less likely to include vegetables and fruits according to some studies. In a study of four- to seven-year-olds, when television and computer time was cut in half, calorie consumption decreased significantly. Among Canadian college students, not only was greater TV viewing linked with more frequent snacking while watching TV, it was also associated with greater consumption of high-calorie snacks compared to students with little TV time. These students also displayed increased advertising awareness, which was the strongest tie to greater consumption of those high-calorie snacks.
Even commercial-free TV is likely to increase calorie consumption, according to experts. When we eat while we are distracted by other activities, we are more likely to continue eating without noticing subtle body signals that we are no longer hungry.