Bile acids have many activities over and above their primary function in aiding absorption of fat and fat soluble vitamins. Bile acids are synthesized from cholesterol, and thus are involved in cholesterol homeostasis. Bile acids stimulate glucagon-like peptide 1 (GLP1) production in the distal small bowel and colon, stimulating insulin secretion, and therefore, are involved in carbohydrate and fat metabolism. Bile acids through their insulin sensitising effect play a part in insulin resistance and type 2 diabetes. Bile acid metabolism is altered in obesity and diabetes. Both dietary restriction and weight loss due to bariatric surgery, alter the lipid carbohydrate and bile acid metabolism. Recent research suggests that the forkhead transcription factor FOXO is a central regulator of bile, lipid, and carbohydrate metabolism, but conflicting studies mean that our understanding of the complexity is not yet complete.