Keywords: weight loss, yo-yo effect, physiology, biomarkers

Weight loss can be achieved easily with dietary intervention, but many people will soon gain that weight back again (the yo-yo effect). Research is needed to identify the causes of this regained weight. This PhD dissertation describes the physiology of weight loss and seeks to identify causes of the yo-yo effect. Contrary to dietary guidelines in various countries, it appears that losing weight quickly (‘crash dieting’) does not lead to faster weight gain afterward than slower weight loss when tracked over a nine-month follow-up period. The rate of weight loss does influence the gene expression of fat cells, which could possibly lead to functional effects. It also appears that higher loss of muscle mass during a diet is related to weight gain during follow-up. Finally, three biomarkers were found that can predict the yo-yo effect to a certain extent.