British Obesity and Metabolic Surgery Society 

• http://www.bomss.org.uk/bomss-nutritional-guidance  

The American Society for Metabolic and Bariatric Surgery

• https://asmbs.org/resources/preoperative-supervised-weight-loss-requirements

Australian and New Zealand Metabolic and Obesity Surgery Society

• https://anzmoss.com.au/

The International Federation for the Surgery of Obesity and Metabolic Disorders

• http://www.ifso.com

National Centre for Biomedical Information > Obesity Surgery 

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4709363/