An epidemic is an illness or contagion that affects a disproportionately large number of individuals within a population at the same time. A pandemic affects all of the people in a large geographic area. During the past 20 years in the United States, obesity has become pandemic, affecting more than half of the population. Currently, more than half of all U.S. adults are considered overweight (defined as BMI 25 to 29.9) or obese (defined as BMI 30 or higher). Body Mass Index is defined as a measure of an adult’s weight in relation to his or her height, specifically the adult’s weight in kilograms divided by the square of his or her height in meters.
Although our society has made great strides in reducing other threats to health, such as smoking, we’ve been unable to stem the rising tide of obesity in the population. This trend is particularly disturbing because obesity is central to the development of many chronic diseases such as type 2 diabetes, heart disease, hypertension, and cancer. Clearly, the increase in rates of obesity is a matter of major public health concern.
Obesity is characterized by an excessively high amount of body fat or adipose tissue. This condition is common, but the condition varies from individual to individual. At one end of the spectrum, a healthy weight can be attained by cutting down on certain foods, taking smaller portions, and embarking on a regimen of regular exercise. For individuals in this population, a moderate change in diet and exercise are the proper interventions because they work.
At the other end of the spectrum, there is another population of overweight people who don’t respond as well to these interventions. Everyone knows someone who tries diligently to lose weight but who experiences limited success or loses weight only to gain it back over time. In fact, more than 80 percent of those who lose weight will gradually regain it. What’s different about these people compared to those who either stay thin or lose weight readily and keep it off with relatively minor lifestyle changes? One difference may be genetic risk factors that affect energy metabolism and result in an inborn susceptibility to gain weight.
Although rare obesity syndromes caused by mutations in single genes have been described, by far the greatest proportion of obesity in humans isn’t due to mutations in single genes. Genetic predisposition may not be health destiny, but studies indicate inherited genetic variation is an important risk factor for obesity. Evidence from twin, adoption, and family studies strongly suggests biological relatives exhibit similarities in maintenance of body weight. Genetic factors also are beginning to be implicated in the degree of effectiveness of diet and physical activity interventions for weight reduction.
Does this mean those with a susceptible genotype are destined to a life of futile efforts to achieve a healthy weight? This need not be the case. We can’t change our genes, but we can change our behavior. Small victories in weight loss—often as little as 10 percent of total body mass—can result in positive effects on health and well-being, even if an ideal weight remains elusive. Also, the positive effects of regular physical activity include lower blood pressure and increased cardiorespiratory fitness even in people who are significantly overweight.
In the longer term, understanding the genetic variations that influence energy metabolism may help us understand the underlying biological factors that affect weight gain and energy expenditure and develop interventions that capitalize on these insights.
Finally, to recognize that obesity may be due to a metabolic condition rather than a flaw in character is important both for the people affected and for society as a whole. After 30 years of internal medicine practice, it’s very clear to me the adage “inside every fat person there is a thin person struggling to get out” is true. People don’t get to be massively obese because of a lack of will power or a character flaw that makes them avoid exercise. And, once they become massively obese, diet and exercise by themselves are rarely effective.
Each of us, no matter our weights, will feel better and be healthier if we engage in a healthy diet and exercise regularly. As leaders of our society, we need to examine how we can enhance opportunities to create and reinforce these behaviors in our homes, schools, work places, and communities. It’s a public health imperative. For more information, visit www.cdc.gov/nccdphp/dnpa/obesity/index.htm. IBI