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Is Obesity Contagious?

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A study published in the July 26 issue of the New England Journal of Medicine contends that obesity is “socially contagious.” In other words, when a person gains weight their close friends are likely to do the same. The study concluded that when the scale reads “obese” for one individual, the odds that their friends will become obese increase by more than 50 percent. Interestingly, the study concluded that the “obese influence” occurs even if the close friend lives hundreds of miles away.

Dr. Nicholas A. Christakis, a physician and professor of medical sociology at Harvard Medical School and a principal investigator in the study, said one explanation was that friends affected each other’s perception of fatness. When a close friend becomes obese, then obesity may not look so bad. “You change your idea of what is an acceptable body type by looking at the people around you,” said Dr. Christakis.

Other interesting insights:

• If one adult sibling becomes obese, the chances that the other sibling will become obese are increased by 40 percent.
• If a spouse becomes obese, the other spouse has a 37 percent increased risk of obesity.

The issue is of no small concern, since obesity has become a major public health problem in the United States and other Western nations. Around the world, the number of people struggling with weight problems is increasing rapidly. Within the US the fraction of the population considered obese has doubled in the past 25 years, from 15% to 32%. Based on World Health Organization definitions, people are considered obese if they have a body mass index, or BMI, over 30.

Obesity is associated with an increased risk for some types of cancer including endometrial (cancer of the lining of the uterus), colon, gall bladder, prostate, kidney, and postmenopausal breast cancer. Women gaining more than 20 pounds from age 18 to midlife double their risk of postmenopausal breast cancer, compared to women whose weight remains stable.

Obesity contributes to increasing levels of lipids (fat) and cholesterol in the blood (hyperlipidemia and hypercholesterolemia respectively), leading to narrowing of blood vessels due to deposition of fatty materials in coronary arteries (atherosclerosis). This in turn causes the blood pressure levels to soar (hypertension) and increases the risk of heart attack (myocardial infarction) and strokes. Overweight people are more likely to suffer from sleep apnea, a condition in which a person snores heavily and stops breathing for small periods while sleeping. This is a serious condition that may lead to heart failure.

Obesity increases the risk of diabetes because it increases insulin resistance leading to glucose intolerance. Weight reduction helps many diabetic patients in controlling their diabetes.

Excess body weight exerts more pressure on joints wearing out the tissue that pads the joints leading to osteoarthritis. Losing weight can provide significant relief from this condition.

Does this mean you should go through your address book and cross out the names of your friends with a BMI greater than 30? Of course not. “We’re not suggesting that people should sever their ties with overweight friends,” says Christakis. “Having friends is healthy for you.” Experts stress that people with more friends tend to enjoy better emotional and cognitive wellbeing.

What this does mean is that if you have close friends who are obese then you should be vigilant about maintaining a healthy weight and healthy lifestyle and encourage your friends to do the same. By supporting each other, you can develop a happy, healthy lifestyle that will add years to your life.