The real causes of heart disease, according to the book "Fat and Cholesterol are GOOD for You!", are not high cholesterol or saturated fat, as commonly believed. Instead, the author, Uffe Ravnskov, suggests that atherosclerosis, the buildup of plaques in the arteries, is caused by microbial infections, the immune system's response to lipoproteins, and various risk factors like smoking, hypertension, stress, diabetes, kidney failure, and elevated homocysteine levels. He argues that cholesterol is not the direct cause of heart disease but rather a marker for other underlying issues. The book also criticizes the effectiveness and safety of cholesterol-lowering drugs and diets, suggesting that they may not be beneficial and could even be harmful.