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Expert Alert

U of M experts weigh in on changes in childhood BMI growth over the 20th century

June 20, 2012

The serving size for a soda is larger today than it was 60 years ago and more and more people sit behind desks all day, only to go home to TVs at night. We can see the effect on the adult population in terms of increasing Body Mass Index (BMI), a clinical and reliable indicator of body fatness, but how do these changes affect children?

Very young children born over the past 30 years may actually have smaller BMIs than children their same age born earlier in the 20th century, but nonetheless are growing up to be a part of the obesity epidemic through rapid growth later in childhood and adolescence.

Are today’s children growing up in a society that predisposes them to obesity? Two University of Minnesota experts who can offer insight are:

Ellen W. Demerath, Ph.D. Associate Professor in the School of Public Health and William Johnson, Ph.D. Research Associate in the School of Public Health.

Johnson recently led an analysis of the differences in BMI growth in children born between 1929 and 1999 in the Fels Longitudinal Study. The findings, which were published in The American Journal of Clinical Nutrition, showed a growing trend of lower BMI values early in childhood followed by faster BMI growth. 

The study compared three generations of children in families:  individuals born during and after the Great Depression, their Baby Boomer children, and their Gen X/Y grandchildren. “Any differences in growth between cohorts must be due to changes in the environment, because genotype is basically held constant by the family-design of the study,” explains Johnson.

Although the analysis could not take into account the dietary and exercise trends of the population, there is historical evidence of environmental changes that could explain why BMI growth in late childhood would be faster now than earlier in the 20th century.

The findings suggest that “Normal BMI as a preschooler doesn’t necessarily protect someone from obesity as a teen or adult,” says Johnson. “Environmental factors like a healthy diet and regular physical activity are key components for a person to avoid obesity.”

To schedule an interview with Johnson or Demerath, contact Laurel Herold, (612) 624-2449,

About the Fels Longitudinal Study:

Initiated in 1929 as a study of child growth and development, the Fels Longitudinal Study follows individuals within families from birth throughout adulthood. To date, it is the longest continuously running study of its kind.

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