Obesity: The Greatest Threat to American Society?

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This week, The Takeaway is exploring America's obesity epidemic. More than two in three American adults are overweight, and one in three are obese. For children, the numbers are better but still grim: An estimated 1 in 6 children are obese.

For some public health experts, this is the biggest problem we face as a society today. 

"Obesity is a complex disease," says Dr. Sam Klein, director for the Center for Human Nutrition at the Washington University School of Medicine in St. Louis. "It's a multi-factorial disease that affects every aspect of our society and is a greater public health challenge than anything else — any virus, any disease, and even terrorism."

There are many factors that contribute to obesity, Dr. Klein says.

"[It's] genetics, hormones, the environment they live in, the job that they have, the availability of food, the taste of food, the commercials for food, our lifestyles," he says. "There are many factors that bombard them 24 hours a day that make it very difficult to change lifestyle habits to consume less calories and lose weight."

Here, Dr. Klein walks us through the science of obesity, and why some people suffer adverse effects from weight gain, and others don't.