A UCSF researcher has determined that a key reason for the epidemic of pediatric obesity, now the most commonly diagnosed childhood ailment, is that high-calorie, low-fiber Western diets promote hormonal imbalances that encourage children to overeat.

In a comprehensive review of obesity research published in the August edition of the journal Nature Clinical Practice Endocrinology & Metabolism, Robert Lustig, MD, professor of clinical pediatrics at UCSF Children's Hospital, says that food manufacturing practices have created a "toxic environment" that dooms children to being overweight.

"It will take acknowledgement of the concepts of biological susceptibility and societal accountability and de-emphasis of the concept of personal responsibility to make a difference in the lives of children," Lustig says.

According to the National Institutes of Health, the number of children who are overweight in the United States has doubled during the past three decades. Currently one child in five is overweight. The increase is true for children and adolescents of all age groups and races and for boys and girls.

Diseases that once were only seen in adults, like type 2 diabetes, now are occurring in increasing numbers in children, according to Lustig. Overweight children tend to become overweight adults, which also puts them at greater risk of high blood pressure, heart disease, and stroke. Children who are obese also are socially ostracized and teased, putting them at risk for depression and other psychiatric conditions, he adds.

"Our current Western food environment has become highly 'insulinogenic,'" Lustig says, "as demonstrated by its increased energy density, high-fat content, high glycemic index, increased fructose composition, decreased fiber, and decreased dairy content."

"In particular, fructose (too much) and fiber (not enough) appear to be cornerstones of the obesity epidemic through their effects on insulin," he adds.

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Lustig says that it has long been known that the hormone insulin acts on the brain to encourage eating through two separate mechanisms. First, it blocks the signals that travel from the body's fat stores to the brain by suppressing the effectiveness of the hormone leptin, resulting in increased food intake and decreased activity. Second, insulin promotes the signal that seeks the reward of eating carried by the chemical dopamine, which makes a person want to eat to get the pleasurable dopamine "rush."

Calorie intake and expenditure normally are regulated by leptin, Lustig says. When leptin is functioning properly it "increases physical activity, decreases appetite, and increases feelings of well-being." Conversely, when leptin is suppressed, feelings of well-being and activity decrease and appetite increases -- a state called "leptin resistance."

Changes in food processing during the past 30 years, particularly the addition of sugar to a wide variety of foods that once never included sugar and the removal of fiber, both of which promote insulin production, have created an environment in which our foods are essentially addictive, he adds.

Lustig also notes that children cannot be blamed or expected to take personal responsibility for their dietary behavior in an environment when the foods they are offered -- especially cheaply prepared "fast foods" that are full of sugar and devoid of fiber -- are toxic.

"The concept of personal responsibility is not tenable in children. No child chooses to be obese," he says. "Furthermore, young children are not responsible for food choices at home or at school, and it can hardly be said that preschool children, in whom obesity is rampant, are in a position to accept personal responsibility."

"If we don't fix this, our children will continue to lose," he emphasizes.

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