Developed by a team of researchers led by Dr Kevin Hall of National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, USA, the new 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. The model provides an accurate representation of how children's energy balance (the difference between consumed and expended energy) affects their weight gain.
Existing models may have greatly underestimated the number of calories overweight or obese children are eating. For example, models currently used by clinicians predict that a 10-year-old girl who is 10 kg overweight but was a healthy weight at age 5 has an excess calorie intake of around 40 kcal per day (about the calorie content of a small apple). The new model, which is based on a more sophisticated understanding of how children's metabolism, growth, and energy expenditure change as they gain weight, estimates that the same overweight 10-year-old is actually eating around 400 kcal per day more than a healthy-weight peer, about the equivalent of a beef burger or medium serving of French fries [1].
The new model also indicates that some children may be able to 'outgrow' obesity during periods of rapid growth, for example between the ages of 11 and 16, without changing their bodyweight. Obese boys who maintain the same bodyweight over this period will tend to normalise their body fat while continuing to grow taller and adding lean tissue mass. However, this effect is much less pronounced in girls, mainly because they lose less body fat during this period than do boys, who have a higher growth potential.
By testing the model against real life data from studies that assessed the effects of various weight loss interventions, the researchers showed that their model provides the most accurate tool developed thus far to predict the effect of calorie intake on weight loss in children. With roughly a third of children in the UK and US [2] thought to be overweight or obese, the new model may provide policy makers and clinicians with a greatly improved understanding of how weight loss interventions -- such as calorie-controlled diets and physical activity programmes -- can most effectively be used to address the childhood obesity epidemic.
According to Dr Hall, "One of the most disconcerting aspects of the global obesity epidemic is the high prevalence of childhood obesity, which carries both health and economic consequences. The model we have developed is a substantial step forward in fighting this rising tide of childhood obesity. It allows us to accurately predict how a child's energy intake affects his or her likelihood of becoming overweight or obese.*
"Though the model doesn't apply perfectly to all children -- for instance, those who start adolescence late, or who undergo particularly rapid weight gain -- it provides an accurate representation of the average effect of reducing or increasing calorie intake on the weight of children. Our future research will adapt the model to individual children as well as study the effects of increasing physical activity along with diet changes."*
Writing in a linked Comment, Professor Claudio Maffeis, of the University of Verona, Italy, points out that the new model suggests that the best time for implementing weight loss plans in children is likely to be before puberty, especially for girls. However, even with the improvements offered by the new model, awareness of children and their parents about their calorie intake must be improved if childhood obesity is to be effectively tackled.
"The accuracy of parents' awareness of children's portion sizes and reporting of children's food intake is only moderate," says Professor Maffeis, adding that, "Reduced awareness of food intake in obese or preobese children and their parents is an important limiting factor in the modification of nutritional behaviour, and associated under-reporting of food intake adversely affects clinicians' planning of adequate dietary strategies…to translate into practice these desired changes in energy balance, it will be necessary to increase families' knowledge and awareness of energy content and composition of childrens' diets by designing effective and sustainable educational programmes about nutrition."
NOTES TO EDITORS
* Quotes direct from author and cannot be found in text of Article
[1] eg, http://www.mcdonalds.co.uk/ukhome/meal_builder.html
[2] http://www.cdc.gov/healthyyouth/obesity/facts.htm and http://www.noo.org.uk/NOO_about_obesity/child_obesity/UK_prevalence
Journal
The Lancet Diabetes & Endocrinology