The ‘adiposity rebound’ concept is wrong and no clinical intervention is needed, says study author: ‘Let’s allow children to grow in peace’
A four-decade-old theory on why children’s body mass index (BMI) ‘rebounds’ and grows from the age of six has been challenged in a new research paper.
The ‘adiposity rebound’ stems from a newborn’s BMI rising rapidly in their first year, before falling to its lowest level at around four years old, before rising so that, by age six, the child has the same BMI as when they were two years old.
This ‘rebound’ happens to all children. However, the timing or age of this fall in BMI in early childhood has been associated with the risk of BMI-obesity in later years.
In 1984 the ‘adiposity rebound’ was proposed, with researchers showing that an early rebound (before age 5.5 years) is followed by a higher adiposity level (having more excessive body fat) than a later rebound (after age seven).
However, a new study has challenged this concept, arguing that increasing muscle mass is behind the ‘rebound’, rather than changes in body fat.
“We do not need to push the adiposity rebound theory in paediatric literature any further because it is not a real disease state or a critical period that warrants clinical intervention. It is a statistical anomaly,” said Prof Andrew Agbaje of the University of Eastern Finland who led the study.
“Fat-free mass or lean mass growth is likely the accurate physiological explanation for the body composition reset that occurs in early childhood. It is a natural phenomenon for survival, which we have erroneously considered a disease process, and we have been trying to treat or prevent it for 42 years. So, the term ‘adiposity rebound’ is wrong, it is a BMI fallacy, it is simply muscle mass build-up or growth.”
Several trials have taken place in the intervening decades regarding this phenomenon that Prof Agbaje’s new evidence shows is non-existent.
In one randomised controlled trial from Finland, starting at seven months of age which continued until age 20 years, an intervention introduced infants to a heart-healthy diet, characterised by low proportional intake of saturated fat and cholesterol, by dietary counselling and nutrition education sessions to parents and children from the age of seven months to 20 years, while the control group received no intervention.
There was no difference between the intervention and control group regarding the ‘rebound age’ – the average decrease in BMI and the subsequent increase by age six.
“This is just one example showing clinical trials could not change the so-called ‘adiposity rebound’ because it is simply a normal part of life and not a disease process or risk,” added Prof Agbaje.
To establish whether this phenomenon is real – or what is really the cause of it – Prof Agbaje in this new study instead used waist circumference-to-height ratio (WHtR), which measures body fat/adiposity with around 90 per cent accuracy compared with the gold standard (dual-energy Xray absorptiometry) measure of fat mass.
He analysed data of 2410 multiracial children aged between two and 19 years from the US National Health and Nutrition Examination Survey (NHANES) 2021–2023 cycle, using both BMI and WHtR measurements.
The mean value of BMI at age two (17.1 kg/m2) was regained by age six after a significant decrease in the four-years in between, which was consistent with the adiposity rebound theory.
However, the WHtR mean value at age two (0.54) was never regained throughout childhood and adolescence. Overall, WHtR falls until age seven, from which age it increases across childhood and late adolescence – but never recovering to the level it was at age two years.
Prof Agbaje says his results show that there is no true rebound in fat mass, and it is an increase in muscle/lean mass that causes the increase in BMI seen around age five to seven, which has been erroneously described as fat or adiposity.
“Children in effect undergo a body composition reset at the plateau around age four years, which prepares them for the growth stages after that age,” he said.
He suggests that the adiposity rebound theory is therefore a BMI-induced ‘false discovery’ similar to the “obesity paradox” in adults, explained as people living with obesity can have lower mortality rates in certain scenarios than people with normal weight.
The BMI obesity paradox emphasises a U-shaped relationship with heart failure and mortality among adults, meaning those with higher BMI are protected from heart disease. However, subsequent research has established that it is the increased muscle mass within the BMI that is a protective factor.
When WHtR was associated with heart failure in randomised clinical trials, the association was linear, meaning that the higher the fat mass, the worse the cardiovascular disease. WHtR is thus better than BMI at identifying fat mass and its associated risk.
“This is a pivotal moment in history in the definition and accurate diagnosis of childhood excess body fat, with the possibility of adopting WHtR as a practical and clinically useful universal tool in diagnosing excess fat in children and adolescents,” said Prof Agbaje.
“Our new analysis suggests that this adiposity rebound phenomenon is not an obesity problem; this is an increase in muscle mass, and it is a good thing for healthy, normal growth. No clinical intervention is needed to address a non-existent problem in children. Let’s allow children to grow in peace.”
The research will be presented at this year’s European Congress on Obesity in Istanbul, Turkey (12-15 May) and has been published in The Journal of Nutrition.
Read the study: Adiposity Rebound or Fat-Free Mass Anabolism in Children—Challenging a 42-Year-Old BMI Puzzle with Waist-to-Height Ratio – The Journal of Nutrition.
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