Child’s weight for life shaped by first 1,000 days, report health experts

A critical window of just 1,000 days – from pregnancy through to a child’s second birthday – has been identified as key to influencing weight patterns that can last a lifetime, according to a timely new report from the UK Academy of Medical Sciences and Italy’s Accademia Nazionale dei Lincei.

The 'Early years interventions to tackle child obesity and promote lifelong health' report highlights that developmental trajectories become more difficult to alter after around age five, making early intervention important as childhood obesity rates reach alarming levels across the UK and other countries. It forms part of the Academy’s broader work on child health and prevention, following the landmark 2024 'Prioritising early childhood’ report and a recent Council for Science and Technology letter on primary prevention to the Prime Minister. Academy President Professor Andrew Morris CBE PMedSci co-chaired the letter, which called for ‘bold political choices’ and coordinated cross-government action to tackle health inequalities at their root, emphasising prevention can be up to four times more cost-effective than treatment.  

This analysis comes as the Government unveils major new measures to tackle widening health inequalities as part of the forthcoming NHS 10-Year Health Plan, with Health and Social Care Secretary Wes Streeting pledging to redirect £2.2bn to deprived communities where health needs are greatest. 

Currently, at least one-in-five children in England, Scotland and Wales are living with obesity by age 10, with rates having steadily increased over the last two decades. Similar challenges are faced in Italy, where 28.8% of children are overweight and 9.8% are living with obesity, demonstrating why international collaboration is essential to understanding this global crisis. 

The report highlights: 

• The first 1,000 days of life are critical – weight trajectories are often established during pregnancy and early infancy due to a combination of genetic and environmental factors. These can be difficult to change after age five. 

• Stark inequality – obesity rates are twice as high in the most deprived areas compared to affluent ones. 

• Public health policy interventions work better than individual programmes - recent reviews show ‘very little evidence’ that diet and exercise interventions targeting individual children achieve sustained weight loss. Instead, systems-based approaches that create environments for children to live a healthier lifestyle can be more effective.  

• Lasting Covid-19 impact – while obesity in 4-5 year olds has returned to pre-pandemic levels, it remains elevated in 10-11 year olds. 

• Life expectancy – a child with severe obesity at age four has a life expectancy of just 39 years. 

Report co-chair Professor Susan Ozanne FMedSci said: “The first 1,000 days, including time in the womb, represent an important window of opportunity to set children on a healthy trajectory for life. Once obesity is established, it becomes increasingly harder to reverse. This isn’t about individual willpower or blaming and shaming – it's about creating an environment for parents, carers and their children that supports healthy development from the very beginning.” 

Professor Rosalind Smyth CBE FMedSci, Vice-President (Clinical) at the Academy of Medical Sciences, said: “As highlighted in this important child health report, childhood obesity, which has life-long impacts on health, has risen considerably across the world. The Academy’s convened leading international experts to consider these trends and propose systems-based solutions. 

“What makes this work particularly significant is how it connects to the Government’s vision of raising ‘the healthiest generation of children’ and its broader ambitions for opportunity and economic growth. When we address health inequalities in the earliest years, we’re not just improving individual outcomes – we're building the foundations for a healthier, more productive society. The evidence reinforces that prevention, which requires a cross-sectoral approach, must be coordinated across all government departments.” 

The new child obesity report was produced with Italy’s Accademia Nazionale dei Lincei following a joint policy workshop, which was funded by the UK Government’s Department for Science, Innovation and Technology. It summarises discussions from leading researchers across Europe and World Health Organization experts to focus specifically on the obesity crisis within the broader context of declining child health. 

The experts call for urgent action on multiple fronts: 

• Pregnancy focus – entering pregnancy with a healthy weight is vital, therefore prioritising support during pregnancy is important. 

• Breastfeeding support – while evidence indicates breastfeeding can be protective against obesity, success depends on creating supportive environments and removing barriers that make breastfeeding difficult for many mothers. 

• Cross-government coordination – rather than targeting individual behaviours, success will likely require policy interventions across food, education, urban planning and transport that reinforce rather than conflict with each other. Policies encouraging physical activity, for example, depend on supportive urban planning and transport policies to create enabling environments for healthier lifestyles.  

• Tackling health inequities – obesity rates are twice as high in the most deprived areas, creating a vicious cycle where children living with obesity face stigma and discrimination that can limit their access to healthcare and opportunities, further entrenching socioeconomic disadvantage. Obesity-targeting interventions could help address this widening gap but require careful design since current approaches often have greater impact among higher socioeconomic groups, risking further inequality. 

• Food policy and legislation – robust regulation of the food industry is needed rather than relying on voluntary agreements, with evidence supporting taxation of unhealthy products and potential subsidies for healthier options. 

The report confirms that 1.3 million UK children are currently living with obesity, with a further 2.3 million overweight. Products marketed for young children are highlighted as areas of particular concern, including follow-on formula milk which contains high sugar content, and sugar-sweetened beverages. The Academy emphasises that success will likely require coordinated interventions targeting multiple factors delivered within supportive systems. 

Report co-chair Professor Paolo Vineis said: “This collaboration between the UK and Italy has revealed that childhood obesity transcends borders – it is a shared challenge requiring coordinated action. The evidence demonstrates that success comes from addressing the systems and environments shaping children’s health, not just individual behaviours.” 

This report follows the Academy’s landmark 2024 report ‘Prioritising early childhood to promote the nation’s health, wellbeing and prosperity', which warned of a ‘gathering crisis’ in child health and called for urgent government action. It revealed that infant survival rates are worse in the UK than in 60% of similar countries, with the cost of inaction estimated at £16 billion annually.