Thus, the most important factor over time is generally the total number of calories. Fats come in several varieties, among them saturated, monounsaturated, and polyunsaturated. Unfortunately I'm not an expert on the subtleties of fat metabolism, but it has been well established that there is an increased risk of heart disease associated with high-fat diets, in particular those high in saturated fat. Diets high in monounsaturated fat, such as the Mediterranean diet, are thought to have a heart-protective effect, but there is still much research going on in this area. Individuals with different pre-existing conditions may have different nutritional requirements.
Simple sugars can pose a much greater risk to health than fats.
It depends on several factors and it can become a very complicated issue - it would take a large book to completly cover this subject. Individuals who are obese, diabetic, or have some form of impaired glucose tolerance may need to watch their ingestion of some foods, but for the general population the primary risks from sugary foods are tooth decay and obesity from an excess of calories. All carbohydrates are converted to glucose before the body can use them for energy, or they are stored as glycogen or fat. The glycemic index - some carbohydrates are absorbed more quickly than others, and it is not always the foods people think that are absorbed quickest. Be careful with the glycemic index, though.