The aim of this project is to generate pilot data for a grant proposal to evaluate the impact of intermittent cold exposure (ICE) on brown and white adipose tissue (BAT/WAT) function in children with non-alcoholic fatty liver disease (NAFLD). The condition NAFLD is the most common liver disease in both adults and children. There are many emerging drug therapies for NAFLD but at considerable cost in terms of potential side effects. In a mouse model of diet-induced obesity, ICE was shown to help activate BAT, which may help NAFLD and other obesity associated health risks. Given that children have more BAT than adults, we hypothesise that intermittent cold exposure via a cooling vest in children with NAFLD will increase BAT stores or function. We will investigate whether intermittent cold exposure via a cooling vest device will stimulate BAT and also establish whether the cooling vest is acceptable to children and young people. If it is acceptable and has an impact on BAT function this could be a new treatment to reduce the severity of metabolic disorders associated with obesity, particularly fatty liver, e.g. hepatic steatosis. In stage 1, we will investigate the impact of intermittent cold exposure (ICE) on brown and white adipose tissue (BAT/WAT) function in young people aged 16 to 26 years old, as a feasibility study to optimise the cooling process. In stage 2, we will investigate the impact of ICE on BAT and WAT function in 8-16 year olds with non-alcoholic fatty liver disease (NAFLD) and matched controls. Participants will have thermal imaging, MRI scans and provide samples before and after wearing the cooling vest.