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Why are we so fat? Well, it’s complicated. . .
March 6, 2010  |  by Elizabeth Evitts Dickinson
Illustration: Leo Acadia

Illustration: Leo Acadia

obesityWhy are we so fat? Well, it’s complicated…

In the last several decades, prosperous nations have experienced a nutrition transition, where the food concern has moved from malnutrition to obesity. Globally, more than 1.6 billion adults and 20 million children under the age of 5 are overweight. In the United States, 66 percent of adults and 16 percent of American children weigh too much, and by 2015, that figure could reach 75 percent of all Americans.
Youfa Wang, associate professor at the Center for Human Nutrition in the Bloomberg School of Public Health, studies the reasons behind this global weight gain. In several groundbreaking studies, he has concluded that the factors leading to obesity are far more complex than mere diet and exercise. “The general public wants one single message, but there is not one single message. It’s complicated,” Wang says.
Take exercise. In a study published in the journal Obesity Reviews last fall, Wang and his colleagues countered the assumption that increased inactivity is the cause of weight gain in American teenagers. Using government survey data from 1991 and 2007, Wang confirmed that while teenagers are not as active as they should be, there was no increase in sedentary activities even though obesity tripled. Time spent watching television actually declined while physical activity in school went up, leading Wang to conclude that other factors, such as increased caloric consumption, could be the root cause.
Three years ago, he and co-author May
Beydoun, a Bloomberg School postdoc, published a paper on the obesity epidemic in the United States for Epidemiologic Reviews. The paper has since become one of the most cited on the topic, in part because the authors asked important questions about how gender, age, ethnicity, and socioeconomics affect weight. They analyzed data from the 1960s through 2004 and found that the percentage of obese adults had risen by nearly 20 percent. When they broke those numbers down by race and gender, key differences emerged. Among African American women, for example, 80 percent were overweight or obese, while that number shrank to just 30 percent of Caucasian women. If gender alone contributed to obesity, Wang observes, those numbers should be the same. So maybe it’s culture? Not so, Wang argues. Compare African American and Caucasian males and the disparity does not exist. “They are the same,” Wang says. Why? “This is what we’re trying to figure out. It’s a multidimensional issue,” influenced by a host of things from culture and heredity to race, gender, geography, and economics.
Wang works to understand the disparities in obesity by first mining data compiled by other studies. For example, he now is in the midst of a four-year grant to analyze the influence of economic and social factors on people’s lifestyles and obesity using survey material gathered by the U.S. Department of Agriculture. He also collects his own primary data and creates intervention-based programs aimed at changing behavior. In an ongoing NIH-funded study, Wang has been assessing the efficacy of a comprehensive, school-based intervention program targeting low-income African American students in Chicago public schools. Not only did the researchers improve the school cafeteria food, they made improvements to the school environment and got parents and teachers more involved. “Compared to the control school, we see obesity is lowered, children’s body mass index is lower,” he says.
It is this last area—changing behavior—where Wang believes efforts should focus. “This country was very effective in controlling the use of tobacco. Obesity is an epidemic, and public policy can be an important factor.”
—Elizabeth Evitts Dickinson
Illustration: Leo Acadia

Illustration: Leo Acadia

In the last several decades, prosperous nations have experienced a nutrition transition, where the food concern has moved from malnutrition to obesity. Globally, more than 1.6 billion adults and 20 million children under the age of 5 are overweight. In the United States, 66 percent of adults and 16 percent of American children weigh too much, and by 2015, that figure could reach 75 percent of all Americans.

Youfa Wang, associate professor at the Center for Human Nutrition in the Bloomberg School of Public Health, studies the reasons behind this global weight gain. In several groundbreaking studies, he has concluded that the factors leading to obesity are far more complex than mere diet and exercise. “The general public wants one single message, but there is not one single message. It’s complicated,” Wang says.

Take exercise. In a study published in the journal Obesity Reviews last fall, Wang and his colleagues countered the assumption that increased inactivity is the cause of weight gain in American teenagers. Using government survey data from 1991 and 2007, Wang confirmed that while teenagers are not as active as they should be, there was no increase in sedentary activities even though obesity tripled. Time spent watching television actually declined while physical activity in school went up, leading Wang to conclude that other factors, such as increased caloric consumption, could be the root cause.

Three years ago, he and co-author May Beydoun, a Bloomberg School postdoc, published a paper on the obesity epidemic in the United States for Epidemiologic Reviews. The paper has since become one of the most cited on the topic, in part because the authors asked important questions about how gender, age, ethnicity, and socioeconomics affect weight. They analyzed data from the 1960s through 2004 and found that the percentage of obese adults had risen by nearly 20 percent. When they broke those numbers down by race and gender, key differences emerged. Among African American women, for example, 80 percent were overweight or obese, while that number shrank to just 30 percent of Caucasian women. If gender alone contributed to obesity, Wang observes, those numbers should be the same. So maybe it’s culture? Not so, Wang argues. Compare African American and Caucasian males and the disparity does not exist. “They are the same,” Wang says. Why? “This is what we’re trying to figure out. It’s a multidimensional issue,” influenced by a host of things from culture and heredity to race, gender, geography, and economics.

Wang works to understand the disparities in obesity by first mining data compiled by other studies. For example, he now is in the midst of a four-year grant to analyze the influence of economic and social factors on people’s lifestyles and obesity using survey material gathered by the U.S. Department of Agriculture. He also collects his own primary data and creates intervention-based programs aimed at changing behavior. In an ongoing NIH-funded study, Wang has been assessing the efficacy of a comprehensive, school-based intervention program targeting low-income African American students in Chicago public schools. Not only did the researchers improve the school cafeteria food, they made improvements to the school environment and got parents and teachers more involved. “Compared to the control school, we see obesity is lowered, children’s body mass index is lower,” he says.

It is this last area—changing behavior—where Wang believes efforts should focus. “This country was very effective in controlling the use of tobacco. Obesity is an epidemic, and public policy can be an important factor.”


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