An Pan's research mainly focuses on the nutritional epidemiology of obesity and obesity-related metabolic diseases, like metabolic syndrome, type 2 diabetes and cardiovascular disease. Using data from clinical trials and several large cohort studies in China, US and Singapore, he has systematically examined the relation of many nutritional components with weight gain, diabetes and cardiovascular disease. Meanwhile, he has been interested to understand the complex relation between depression and various metabolic diseases, and have proposed the bidirectional relations of depression with obesity, metabolic syndrome and diabetes. He also has a broad interest in other potential risk factors for obesity and metabolic diseases, like occupational and environmental factors (shift work, incense use, heavy metals) and lifestyle factors (smoking and physical activity). Lastly, early-life determinants of metabolic diseases (Development origin of health and disease, DoHAD) have also been on his current research agenda.