US researchers conducting a randomized controlled trial found that adults weighing above the healthy range could burn more calories by watching less television: trial participants who cut their television viewing time in half were more active and on average burned an extra 120 more calories a day.

The study was the work of researchers at the University of Vermont in Burlington, and appears in the 14 December issue of the Archives of Internal Medicine. The US Department of Agriculture's Hatch Funds Act and the National Institutes of Health funded the research.

Lead author Dr Jennifer Otten, who is now a postdoctoral scholar at the Stanford Prevention Research Center, told the press that:

"Taking away time spent in front of the television has the potential to improve a person's activity levels."

The average American adult spends 5 hours a day watching TV: the third most time consuming activity in the US, after sleep and work.

TV uses up fewer calories than doing other sedentary activities, including desk work, chatting on the phone, reading and writing.

Otten said that the more time adults spend in front of the TV, the more likely they are to become obese and suffer from diabetes and cardiovascular disease.

She and her colleagues looked at how reducing the amount of time spent watching TV affected calorie consumption, energy expenditure, body weight, time spent asleep, and the balance beween calorie intake and activity in adults who were overweight or obese.

For the randomized controlled trial they recruited 36 adults who according to self-reports watched a minimum of 3 hours and an average of 5 hours of TV a day, and who had a BMI in the range 25 to 50, which lies beyond the healthy range and includes overweight (BMI between 25 to 29.9) and obese (BMI of 30 and above).

BMI (Body Mass Index) is the ratio of a person's weight in kilos to the square of their height in metres.

After monitoring the participants for three weeks, the researchers assigned just over half of them (20 participants) at random to cut their TV viewing by 50 per cent for another 3 weeks, while the rest (16) became the control group and continued as before.

The TV watching time in the intervention group was controlled with an "electronic lockout system" that automatically cut TV viewing by 50 per cent, according to the baseline observed for each participant during the pre-randomization phase.

Also, during the last week of the 3-week intervention period, all participants wore armbands monitors that measured their activity levels, and they kept sleep logs and completed telephone surveys about their diet.

The results showed that:
  • Both groups reduced their energy intake, the intervention group by 125 calories per day (kcal/d) and the control group by 38 kcal/d, although this was not statistically significant.

  • The intervention group significantly increased energy expenditure by an average of 119 kcal/d (95 per cent confidence interval, CI, ranged from 23 to 215) compared with controls, whose energy expenditure went down by an average of 95 kcal/d (95% CI ranged from -254 to 65) (P=0.02).

  • These trends led to a negative energy balance (ie used more than they consumed) in the intervention group but a positive one in the controls (ie consumed more than they used).

  • There was a greater reduction in BMI in the intervention group (-0.25, 95% CI from -0.45 to -0.05) than in the control group (-0.06, 95% CI from -0.43 to 0.31) but this was not statistically significant (P=0.33).

  • There was no change in sleep.
The authors concluded that:

"Reducing TV viewing in our sample produced a statistically significant increase in EE [Energy Expenditure] but no apparent change in EI [Energy Intake] after 3 weeks of intervention."

Otten said that the 120 calories a day of energy the intervention group burned off when they halved their TV viewing was the " equivalent to walking more than a mile".

"We don't know if these short-term changes will translate, but the results may be similar in a longer term study and could prevent weight gain," she added.

Longer term studies in children have shown results consistent with short term studies on TV reduction, and found that instead of increasing activity, children ate less and lost weight that way. Otten said this could be because children have more flexible diets, or they are more susceptible to cravings induced by advertising, or they are generally more active.

Dr Tom Robinson, who has conducted TV studies in children and is the Irving Schulman Endowed Professor in Child Health at Stanford's School of Medicine, said:

"We've known for a decade that reducing children's television viewing is one of the most effective ways to prevent weight gain, so it is great to finally see a study like this in adults."

He said Otten and her colleagues have shown that:

"Reducing TV viewing has the potential to be as important for controlling adult obesity as it is for children."

"Effects of Television Viewing Reduction on Energy Intake and Expenditure in Overweight and Obese Adults: A Randomized Controlled Trial."
Jennifer J. Otten; Katherine E. Jones; Benjamin Littenberg; Jean Harvey-Berino.
Archives of Internal Medicine, 2009;169(22):2109-2115.
Vol. 169 No. 22, Dec 14/28, 2009

Source: Stanford School of Medicine.

Written by: Catharine Paddock, PhD