Glucose Tolerance Factor. GTF is thought to be a complex of chromium, nicotinic acid, and the amino acids glycine, cystein and glutamic acid (these aminos are components of gluthathione). GTF is thought to be synthesize by the liver. In many people, chromium is likely the deficient substrate for GTF formation. GTF is found in foods such as organ meats, whole gains, cheese, mushrooms and brewer's yeast.