The first two decades of life are biologically unique because of the complex interaction between genes and environment driving, partly via hormones, the mature phenotype of an individual. During this time, body weight and composition change rapidly and are particularly sensitive to obesity-promoting factors. In The Lancet Diabetes & Endocrinology, Kevin Hall and colleagues1 present a model that allows for the simulation of body weight and energy balance dynamics in children and adolescents.

Their model showed that, contrary to common perception, the energy needed to accrue body weight in excess of that gained through normal growth is higher than the energy content of the extra mass accumulated. This finding is explained by the higher energy requirement associated with increased body weight. Higher fat-free mass increases basal energy requirements;2 higher body mass increases energy requirements for physical activity (ie, weight-bearing activities);3 and higher food intake (as a result of increased energy requirements accompanying weight gain) increases the energy used for digestion, absorption, and processing of food ingested (ie, meal-induced thermogenesis).4 Increased energy is also spent on synthesis of new tissue.5 Therefore, the requisite energy to gain extra weight rises as the amount of weight gained increases.6 All these factors reduce the positive energy balance, thereby decreasing the speed and intensity of energy-storing processes during the dynamic phase of obesity development.

Hall and colleagues’ model showed that the extra energy intake required for excess weight gain in children is higher than that required in adults, emphasising that, in general, the dynamic phase of excess weight gain in children results from a pronounced increase in energy intake with respect to energy requirements for healthy-weight, age-matched peers. This observation contrasts with those on which standard clinical practice is based and has important consequences. Obese children and adolescents usually report similar food intake to non-obese peers. However, the results of studies7, 8 in which stable isotopes are used to measure total energy expenditure in normal life show that the food intake of overweight or obese children and adolescents is under-reported. Furthermore, the accuracy of parents’ awareness of children’s portion sizes and reporting of children’s food intake is only moderate.9, 10 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. This issue should be addressed with the family as a crucial target of behavioural intervention, because it is not plausible to expect diet adherence when awareness of portion size and daily food intake is low.

Another important simulated finding of Hall and colleagues’ model is the difference between sexes in terms of changes in body composition with weight loss at puberty. At puberty, fat-free mass increases much more in boys than in girls, and thus the energy requirements of boys increase more than those of girls. Thus, if energy intake is kept constant, overweight boys could reach a healthy body composition after maturation (ie, outgrow obesity). However, attainment of healthy body composition for overweight girls through maintenance of a constant energy intake is more difficult without weight loss. The practical implication of this finding is that dietary treatment of obese and preobese children at puberty should differ between sexes and be tailored to individual energy requirements.

Hall and coworkers’ results support more accurate assessment of energy intake and comparison of these estimates with energy requirements calculated specifically for each child. They also provide suggestions for public health strategies for the prevention and treatment of childhood obesity. In particular, their results suggest that the best time for intervention is before puberty, especially in females. The energy imbalance gap is different for universal prevention, prevention in at-risk individuals, and treatment of obesity. Hall and colleagues’ model might help to identify expected energy requirements and, by extension, to calculate the energy imbalance gap to target. However, 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.

Source: Lancet