Childhood obesity is reaching alarming proportions in many countries and poses an urgent challenge to healthcare systems. Obesity affects a child's immediate health and quality of life, and children with obesity are also five times more likely to remain obese as adults compared with those without childhood obesity. Mothers' pre-pregnancy body mass index (BMI) is a strong risk factor for childhood obesity and accounts for more than 20% of childhood obesity cases, implying a strong mother-to-child transmission of obesity. Genetics partly accounts for the risk for obesity, but environmental factors during the time in the womb and early after birth also influence the risk of childhood obesity. In fact, the period from conception to 2 years of age, known as 'the first 1000 days', is the most critical period for development of disorders that lead up to obesity in childhood and later life. The premise in the ExMilk project is that breastmilk is nutritionally optimal for infants, including those who were born to women with overweight/obesity. However, based on recent evidence of differences in breastmilk composition between mothers with high and low BMI, our aim in the ExMilk project is to improve the breastmilk composition in women who are overweight or obese.

In this ambitious, inter-disciplinary project, we will determine how exercise during lactation influences breastmilk composition in women with overweight/obesity and whether exercise-induced changes in breastmilk will influence infant obesity risk. In ExMilk, we will determine both acute effects and adaptations after regular exercise on a complex matrix of breastmilk components. By linking breastmilk data to comprehensive data for the infants, we will investigate the potential mechanisms underlying the effects of maternal exercise on infant obesity risk, mediated by changes in breastmilk composition. To reach our goals, we will perform gold-standard randomised trials and analyse biological samples from mothers and infants on several analytical platforms. Our interdisciplinary expertise will enable us to break new ground in understanding how exercise during lactation modifies infant obesity risk.