Fats and oils are an essential food but they can also kill us. Several myths about them became hugely popular in the late twentieth century. We have been learing a lot more: the truth might save your life.
FATS ARE NOT FATTENING! Amazing but true. When we eat fats and oils they pass into our blood as cholesterol. But any cholesterol we don't use passes them right back into our lower intestine where we get rid of them. They actually help to keep us regular! Well, this is not quite the whole story: noticeably high-fat diets do tend to make you put on a bit more weight, but exactly what is going on there is unknown, it's not a simple eat it–wear it relationship. All things in moderation!
The main body fat we all hate comes from carbohydrates, "carbo" for short - sugar and starch. Besides the sugar we eat, our gut breaks starch down into sugar, and all that sugar passes into our blood. Once there, unlike fats we can't get rid of it. Special body cells convert it into fat so that they can store it until needed. This fat stays in the cell and so the blood can't send it for disposal. This is why we get fat, because we eat too much starch and sugar! It is better to eat one slice of buttered toast than two slices with no butter or marge. The fats and oils will help you feel full - they make food taste so much richer! - and so you won't miss that second slice. Try it!
But not all fats are good. Some, especially the industrially-created trans fats, are bad. There are three classes of fats and oils in our diet; omega oils, trans fats and saturated fats. We call them a fat or an oil depending on whether they are solid or liquid at normal temperatures. Some, such as palm fat, may be called the other - palm oil - in the tropical countries where they come from and the climate is hotter!
Cholesterol is a partticular kind of fatty substance. But the word is commonly also used for the stuff (lipoproteins) that carries all fats around in your bloodstream, whether from your gut to where it's needed or back to your liver or lower intestine for disposal. The stuff that carries them in is often called "bad cholesterol" because too much of it was thought to lead to heart attacks and strokes, while the stuff that carries them out got called "good cholesterol". But things are a lot more complicated than that. In fact, now that we are learning how the real problem is down to too much starch and sugar (see above), the whole cholesterol thing has become a shambles with changing approaches to research leading to conflicting advice everywhere, never mind people using the word incorrectly.
Omega oils are "unsaturated fats" and are essential to health. They occur naturally in many foods, especially nuts, seeds and seafoods. In fact almost all the oils we use in our food are - or should be - omega oils.
Fresh omega oils often smell nice, but as they age they begin to smell fishy.
See also some more detailed information on essential oils and seeds and seed oils (including nuts).
They can be turned into "trans fats" (see below), to some extent by accident when frying or grilling, but usually through industrial processing.
A few trans fats occur naturally, such as in organic milk and cream. Little reearch has yet been done to confirm whether these are safe or not, but there is no known fat-based health risk associated with these foods. Small amounts are also produced as a byproduct of frying and grilling.
See also some more detailed information on trans fats.
This has been the biggest surprise in recent years. Saturated fats have no "omega" markers and are usually hard at room temperature. Early researchers noticed they seemed to be associated with clogged arteries, strokes and heart attacks, so everybody was told not to eat them. But that was before we realised that we were making trans fats and mixing the two together - the trans fats were harming us but the saturated fats were getting the blame.
Saturated fats also have a long shelf life and, being hard, make excellent "shortening" for all kinds of foods such as cakes, biscuits, margarine, ice cream, etc. They are also temperature-resistant and great for frying. But most come from animals as lard, dripping, etc. and so many producers seek vegetable-based alternatives to lower costs and widen their market. But few vegetable fats are saturated, exceptions being palm fat and coconut oil. This was why trans fats were invented, as a cheap and readily-available ingredient in processed foods. Once we realised that the bad health effects were mainly down to trans fats, we began to discover that at least some saturated fats are good for you after all.
Updated 18 Nov 2017