Television = Obesity?

In a previous article, Fat Americans, we presented some information on the demographic correlates of obesity among Americans.  There are other correlates of obesity.  The following is an interview in the magazine Hypatia with Dr. Bernardo Hernández Prado, a social psychologist from UNAM Iztapalapa:

Hypatia: How did you became interested in analyzing the effects of television in the obesity in our state?
BHP: This arises from my Ph.D. thesis theme, that addresses physical activity and obesity in children and teenagers, mainly. With the data obtained from the nutrition surveys, as well as some other specific studies, we made several works. Among them you can find an investigation in Mexico City on obesity related factors, in elementary school students. We found a very high association between the time spent watching television and the obesity. Recently we had the opportunity to duplicate this study in the teenage population of Morelos, as part of a study of youth integral health, coordinated by the INSP.

Hypatia: And what did you concluded?
BHP: Finally, we documented that the prevalence of obesity in the teenagers of Morelos is high, it represents the 25% of its student population. This data resembles the data obtained in Mexico City, where we found a risk factor in the time spent watching television; and a protector factor in the physical activity. I was amazed by the time spent watching television, according to the survey, it ranges from 3 to 4 hours daily. The time spent in front of the T.V. has a peak activity on weekends. Friday and Saturday are television days.

Going back to the same MARS study that was cited in our previous article, we looked at the correlation of television viewing with obesity.  The MARS study is a general population survey of adults living in the 50 states of the United States of America.  Within this sample of 22,097 adults, 7.9% said that they are diagnosed as being obese.  Among those who are obese, their average time spent viewing television is 5.1 hours per day; among those who are not obese, their average time spent viewing television is 4.3 hours per day.  This is a statistically significant difference.

A visual way to present this information is through the use of media quintiles.  Here, the respondents have been sorted into quintiles (top 20%, next 20%, ... , bottom 20%) on the basis of the amount of television viewing per day.  As shown in the first chart below, the amount of television viewing will increase as we move up the quintiles by definition.  Then in the next chart, we show the incidences of obesity in the same quintile groups.  The incidence increases as we move up the quintiles by definition.

Of course, we are not so naïve as to subscribe to a theory whereby invisible particles are emanating behind the television screen to impinge upon the captive human audience in front of the set, thereby modifying their metabolic processes so as to render them obese.  From the same Hypatia interview, we read:

Hypatia: What recommendations would you give to parents and authorities on this situation?
BHP: First of all, that parents should carefully watch what their children eat. Especially high calorie and high fat content meals. At the same time, authorities should empower measures and policies in the selection of food during television schedules, as well as promote sport and healthy practices that encourage physical activity. In Cuernavaca, there aren't practically any places where children and teenagers might practice sports; hence, improving their overall development.

Therefore, one mechanism that explains the correlation between television viewing and obesity is the reduced energy expenditure from the displacement of physical activity by televising viewing.  To this we can add the increased dietary energy intake during those extended episodes of passive television viewing.  In the next chart, we show the information from the MARS study about the incidence of obesity among people who have participated in various leisure activities over the previous year.  Whenever the leisure activity involves significant physical exertion, the incidence of obesity falls below the population average.  An unexplored additional mechanism is the effect of food advertising on television, which induces over-consumption.

(posted by Roland Soong on 03/16/2003)