Longitudinal studies provide unique insights into the impact of environmental factors and lifespan issues on health and disease.Here we investigate changes in body composition in 3,088 free-living participants, part of the UK Biobank in-depth imagingstudy. All participants underwent neck-to-knee MRI scans at the first imaging visit and after approximately two years (secondimaging visit). Image-derived phenotypes for each participant were extracted using a fully-automated image processing pipeline,including volumes of several tissues and organs: liver, pancreas, spleen, kidneys, total skeletal muscle, iliopsoas muscle,visceral adipose tissue (VAT), abdominal subcutaneous adipose tissue (ASAT), as well as fat and iron content in liver, pancreasand spleen. Overall, no significant changes were observed in BMI, body weight, or waist circumference over the scanninginterval, despite some large individual changes. A significant decrease in grip strength was observed, coupled to small, butstatistically significant, decrease in all skeletal muscle measurements. Significant increases in VAT and intermuscular fat in thethighs were also detected in the absence of changes in BMI, waist circumference and ectopic-fat deposition. Adjusting fordisease status at the first imaging visit did not have an additional impact on the changes observed. In summary, we showthat even after a relatively short period of time significant changes in body composition can take place, probably reflecting theobesogenic environment currently inhabited by most of the general population in the United Kingdom.