BOSTON – Over the past several years, animal studies have shown that high-fat, low-carbohydrate “ketogenic” diets cause demonstrable changes in metabolism and subsequent weight loss. Now, researchers at Beth Israel Deaconess Medical Center (BIDMC) have identified a key mechanism behind this turn of events. Their findings, which appear in the June 2007 issue of Cell Metabolism, demonstrate that a liver hormone known as FGF21 is required to oxidize fatty acids – and thereby burn calories.