Though the president of the United States is arguably the most powerful man in the world, his wife wields considerable influence. Each First Lady usually has a pet social cause they wish to champion. Nancy Reagan famously tackled America's drug problem, for example, and Michele Obama recently launched a campaign to reduce childhood obesity.

It's a serious and growing problem. Childhood obesity has more than tripled in the past 30 years, according to the U.S. Centers for Disease Control and Prevention. Obesity among children aged 6 to 11 years increased from 6.5 percent in 1980 to 19.6 percent in 2008.

A study released earlier this month found that one in five American teenagers has abnormal levels of cholesterol and therefore an increased risk of heart disease. Other weight-related diseases typically associated with obesity – including high blood pressure, diabetes, and arthritis – are being found in younger and younger teens.

As part of her effort to highlight the problem, Mrs. Obama personalized the issue in a speech, drawing from her own family's experience. Her children's doctor suspected that the Obama girls were overweight; this was confirmed by a medical analysis called the Body Mass Index (BMI). Minor changes were made to the girls' daily lives, including a diet change and getting more exercise. The girls soon achieved a healthy weight, and all was well. The anecdote was intended to be an inspiring personal success story, but some criticized Mrs. Obama for personalizing the issue by mentioning her daughters' weight.

For example, a woman named Laura Collins Lyster-Mensh wrote a blog on the Huffington Post titled, "What the Eating Disorder World Wants Mrs. Obama to Know." In it, she railed against Mrs. Obama for having put her overweight daughters on a diet, stating, "In the eating disorders world, putting any child on a diet is not only unacceptable but appalling.... I am sucker-punched to read that our First Family put their daughters on a diet because they feared obesity."

Lyster-Mensh believes that people who follow Mrs. Obama's actions will damage the self-esteem of girls who are told they are overweight, and likely trigger a downward spiral into eating disorders.

Yet Lyster-Mensh, who is not a doctor, misunderstood both the First Lady and the situation, apparently believing that the Obama children were put in a calorie-restrictive starvation diet.

In fact, a review of Mrs. Obama's comments makes it clear that she was referring to the girls' diet in the nutritional sense: eating healthy food in moderate portions, reducing sugary drinks, adding more fruits and vegetables to the diet, and so on — along with limiting television time and increasing exercise. These are exactly the sorts of things doctors advise.

Furthermore, eating disorders such as anorexia nervosa and bulimia usually affect normal-weight individuals, not the obese. Neither of the Obama girls have been diagnosed with an eating disorder, and the general incidence of anorexia is only about 1 to 2 percent of the population. Obesity is far more prevalent than anorexia at all ages, and the average child or teenager is in much greater danger of developing health problems associated with obesity.

The idea that parents, doctors, and teachers should avoid telling children they are overweight for fear of hurting their feelings is both dangerous and misguided.

The concern that children and teens have low self-esteem is a popular myth that has been conclusively disproven. Numerous studies show that about 90 percent of teens feel good about themselves, and fewer than one-fourth of Americans are dieting at any given time. Yet two-thirds are overweight or obese, and more children are joining that group every day.

Mrs. Obama's actions — and advice — were recommended by their pediatrician, and are exactly appropriate not only for America's children but adults as well.

Benjamin Radford is managing editor of the Skeptical Inquirer science magazine. His books, films, and other projects can be found on his website. His Bad Science column appears regularly on LiveScience.