I’m going to steal this one right from the /r/keto FAQ:
All foods containing fat – even pure oils – contain a mixture of three kinds of fat:
- polyunsaturated, and
We often identify foods by their predominant fat. For example, olive oil as “monounsaturated” butter as “saturated” – but all real foods contain mixtures of the three.
All three types of fats are necessary and important to human health. We should incoporate them into our diet in a balanced proportion. That’s the big question: What is balanced?
- Saturated fat, particularly in the absence of high carbohydrate intake, is not dangerous to human health. When balanced with mono and polyunsaturated fats in a controlled carbohydrate dietary environment, saturated fat has real and measurable benefits. You quickly oxidize saturated fat into energy, once you are keto adapted. So you can enjoy plenty of butter and animal fat guilt-free. Interestingly, coconut oil is something very different: it consists of Medium Chain Triglycerids (MCT) which your body cannot store. It has to immediately oxidize it. That means your body will immediately produce ketones, even when you are not keto-adapted. Nevertheless, this does not mean you’re getting all the metabolic advantages that you would get in a keto-adapted state.
- Monounsaturated fats (like olive oil) have well-known and well-documented benefits.
- Polyunsaturated fats, like vegetable oils, usually contain a lot of omega-6 and very little omega-3. The ideal ratio between omega-6 to omega-3 is 2:1 to 1:1. Generally, this ratio is often 20:1 or even worse. It is therefore important to avoid oils high in omega-6, like corn or soy. Vegetable oils rich in omega-3 contains it in the form of ALA which the body has to convert to DHA and EPA to be of any use. This conversion is highly inefficient. Therefore, ALA omega-3 rich vegetable oils like flaxseed oil or canola are no good either. The best way to get omega-3 is through fatty fish like salmon, or with a DHA + EPA supplement.
As a general rule of thumb, avoid fats high in omega-6. Also, run like hell from highly processed fat (anything that says “hardened” or contains trans-fats) like margarine. Eat foods naturally high in fat like meat, fish, and nuts; use plenty of olive oil and butter. In fact, 50% butter with 50% olive oil approximates quite closely the composition of body fat. Meaning, this is the type of fat that the body can make best use off.