In recent years, the rate of childhood obesity has risen rapidly in western countries. Systematic review showed that childhood obesity is associated with adult obesity and various adverse health outcomes in adulthood. In fact, overweight and obesity, and the relevant non-communicable diseases are largely preventable. Research has shown that infant and young child feeding is one of the important variables associated with early growth trajectory and later overweight and obesity. A pragmatic challenge of many previous studies is that Body Mass Index ((BMI); an indicator of obesity and overweight) is assessed at one point in time, which did not account for changes in BMI over time. The BMI Z score trajectory overcomes the limitations of static analysis and allows comparisons across ages. However, there are few studies exploring the association between infant feeding and BMI Z score trajectory in the UK. Relevant studies in other countries have different findings on the effects of complementary feeding and duration of breastfeeding on BMI Z score trajectory. It is controversial whether feeding pattern has an effect on BMI among children. No study has been found to explore the independent effect of the feeding pattern (on-demand vs. schedule) on BMI Z score trajectory among children.