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Friends & Body Image
Tuesday, March 11, 2008
Two out of 3 adult Americans are either overweight or obese. One of 3 American children is overweight or obese. Obesity can be defined as having a body fat of greater than 30% in a woman or greater than 25% in a man. Calculating body fat relies on equipment (such as skin calipers, hydrostatic weighing equipment, or a DEXA machine) that may not be readily available, may entail some cost, and usually require experienced personnel to do the calculation of body fat percentage. It is easier for most people to judge whether they are normal weight, overweight, or obese by calculating their body mass index (BMI). The BMI is a measurement based on a ratio of weight to height. To obtain the BMI, divide the weight in kilograms by height in meters squared. (Alternatively, divide the weight in pounds by height in inches squared and multiply by 703.) Obesity can also be defined as having a body mass index (BMI) of 30 or higher. Overweight is defined as having a BMI of 25-29.9. A healthy BMI is considered between 18.5 and 24.9.
The prevalence of overweight and obesity has increased significantly in recent decades. Data from the National Health and Nutrition Examination Survey show that the weight of the average woman increased by 20 pounds between 1976 and 2000. Just since 1994, the percentage of adult Americans that is obese has increased by 8 points. About 1/3 of adults are currently obese. Obesity raises the risk for many chronic diseases, including cardiovascular disease; Type 2 diabetes; osteoarthritis; and hypertension. Obesity is an independent risk factor for having a heart attack. It also increases the chance of having a stroke. Gallstones, elevated blood cholesterol, and fatty liver disease are more common in those who are obese.
There are both genetic and environmental factors that determine an individual’s body weight. A recently published study in the New England Journal of Medicine (
This study involved a detailed analysis of a social network consisting of 12,067 individuals over a 32 year period, from 1971 to 2003. Data were obtained from the Framington Heart Study. (The study was funded by the National Institute on Aging.) The study focused on 5124 individuals (the “egos”), along with their parents, children, siblings, spouses, and close friends (the “alters”). This created a network of 12,067 people. The average age of the key participants at the beginning of the investigation was 38 years; the range was 21-70 years. The investigators knew the weights of the participants, and they also had information about the chain of friendships of the key participants, their spouses, family members, and neighbors.
The results speak to the impact of environment on the prevalence of obesity. Friends were more influential than family. A key participant’s chance of becoming obese was increased by 57% if she or he had a friend who became obese. When the friendship was considered close by both the key participant (the “ego”) and the friend (the “alter”), the key participant’s risk of developing obesity rose by 171%. The chance of an ego becoming obese was increased by 40% if a sibling became obese, and the chance of obesity rose by 37% if a spouse became obese. An immediate neighbor’s becoming obese was not a factor: the key participant was no more likely to be obese if his or her neighbor became obese.
Geographic proximity did not predict the influence of the alter on the ego with regards to the statistical chance of developing obesity. Close friends living miles away could exert more of an impact on the observed relative risk for obesity than immediate neighbors or spouses. The results suggest that social networks may be a factor in the obesity epidemic in the U.S. People are not isolated beings; they are part of a larger whole. The authors note that just as people are connected, so is their health connected. A social network may work to encourage bad behaviors, but it can also encourage desirable behaviors. Studies have shown that smoking- and alcohol-cessation programs that provide peer support are more successful than those that do not. The same may be the case for weight loss and weight maintenance. If several individuals in a group practice healthy lifestyle choices, there is a greater chance of others in that same social network following suit.
Another study, published in the journal, Economic Inquiry, describes changes in the prevalence of obesity in recent years. (Economic Inquiry, 2007, vol. 45, issue 3, pages 571-591) The authors note that the increasing prevalence of obesity from 1976 to 2000 is not explained be changes in the gene pool. They provide a mathematical model that includes environmental factors, including economic and social factors, in addition to biological ones.For more information about these studies and obesity, see the following links: