Growth Spurts May Wipe Out Obesity

Published: Jul 29, 2013 | Updated: Jul 30, 2013

By Cole Petrochko, Staff Writer, MedPage Today
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

Obese children, boys in particular, may be able to "outgrow" the condition, according to a new model of childhood weight gain.

The model showed that during periods of rapid development, from ages 11 to 16, children can lose the "obesity" designation without losing weight, simply by growing taller and adding lean tissue mass, according to Kevin Hall, PhD, of the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Md., and colleagues.

However, the effect was less pronounced in girls, most likely because they lose less body fat during this growth period than boys do, the authors wrote online in The Lancet Diabetes Endocrinology and in an accompanying statement.

They pointed out that the current model "is the first to differentiate between the healthy weight gain that is normal in childhood, and the excessive weight gain that results in overweight and obesity."

Prior models of adult metabolism and the effects of weight control interventions on body weight have been able to accurately predict development, though these models do not account for rapid growth in children. Additionally, other models predicting childhood development "could not adequately distinguish healthy growth from excessive weight gain and were not validated with data other than those used to build the model," the authors noted.

They created a new mathematical model of childhood energy balance and the development of obesity, which accounted for changes in body weight based on calories consumed and energy spent through physical work and daily living, as well as "metabolic adaptations that occur during weight gain and loss and partitions energy imbalances between fat and fat-free masses." The model was also adjusted for halted growth in early adulthood and a higher resting metabolic rate compared with adults.

The model simulated growth through a gradual increase in energy intake from ages 5 to 18 of 1,200 kcal per day over that period in boys and 900 kcal per day in girls. Data from the model were cross-referenced with data from 292 healthy white boys and girls from a study reported by Kenneth Ellis, PhD, of Baylor College of Medicine in Houston, and colleagues.

Excess weight gain and obesity were not clearly defined in the model due to the variability of healthy growth in children as well as the trajectories of excess weight gain, they noted. Obesity was simulated by gradually increasing the rate of energy intake and was shown to increase energy expenditure by 300 kcal per day versus healthy children at 10-years-old.

At ages 5 to 11, the mean energy intake was about 750 kcal per day higher in obese boys versus healthy weight boys, and roughly 850 kcal per day higher in obese than in healthy weight girls. At the end of the simulated 6-year period, obese boys and girls were predicted to eat 1,100 kcal per day and 1,300 kcal per day, respectively, compared with their healthy weight counterparts.

The authors also modeled a child "outgrowing" obesity through a simulation of decreased energy intake. This decrease was held from ages 11 to 16 and accounted for rapid growth during those years. Boys in the simulation had a body composition that "was almost normalized relative to healthy weight boys" and implied that "fat-free mass increased substantially during concomitant loss of fat mass."

Obese girls in this simulation lost less fat over the same period of time under the same parameters as obese boys.

They noted that this may be due to an additional accumulated 9 kg of body fat in girls versus boys at age 11, which would require a change in body weight to achieve similar weight normalization, and that boys achieve rapid growth at a different age than girls, who also create more fat-free mass than girls.

A comparison of body weight between children in two time periods (from 2003 to 2006 versus 1976 to 1980) showed that body weight across all ages increased by an average 6.1 kg in boys and 5.7 kg in girls, which was associated with an average 210 kcal per day increased energy intake in boys and 190 kcal per day increased energy intake in girls.

They noted that these data could show that "reducing energy intake in a cohort of children by a mean of around 200 kcal compared with that in 2003 to 2006 data will return the mean body weight to levels characteristic of the late 1970s -- before the onset of the obesity epidemic."

In an accompanying editorial, Claudio Maffeis, MD, of the University of Verona in Italy, pointed out that this model shows the energy intake required for childhood weight gain is higher than that of adults, but noted that caloric intake of obese children is generally under-reported and "can affect clinicians' planning of adequate dietary strategies."

Parents should be more aware of their child's energy intake and diets to better inform physicians prior to developing a strategy to combat obesity, Maffeis warned.

The best time to offer interventions for weight is prior to puberty, the authors and editorialist agreed.

The simulated interventions were limited to reductions in energy intake, the authors cautioned, but added that energy expenditure was accounted for in their model and the addition of physical activity interventions could be included in future research.

They also noted that the study was limited by use of average data on age and growth and did not account for early puberty or overweight and obesity accumulated through different "weight gain trajectories." The authors noted that different trajectories could be accounted for through the model.

The study was supported by the Intramural Research Program of the NIH and the National Institute of Diabetes and Digestive and Kidney Diseases.

Hall was supported by a U.S. patent application assigned to the NIH.


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