Whether on a low-fat high-carbohydrate diet (HCLF) or on a low-carbohydrate high-fat diet (LCHF)(see more: Kickstart your basic keto diet), you’re going to be eating fats (fatty acids).
Some of these are essential, which is why we talk about essential fatty acids (EFAs). You don’t actually need that much of them, maybe less than 1% of total calories . As these are essential fatty acids  they need to be balanced .
What are the essential fatty acids for humans?
Here, essential means that we need to eat them because our bodies can’t make them from other stuff (or can’t make enough). This definition is straightforward but in practice, it’s a little more complicated.
All essential fats are PUFAs (polyunsaturated fats). They’re delicate, easily messed up by excessive heat or sunlight. The simple case is the omega-6 linoleic acid (LA)  which is the starting point to make other kind of fatty acids that become all sorts of important things, like inflammatory molecules that help you fight infections.
You need very little of it. Simply eating meat, fish, vegetables, nuts and fruit will suffice. A more complicated case is the omega-3 alpha-linolenic acid (ALA) found in plants, such as flax . We have the machinery (a series of enzymes) to turn ALA into two particularly important molecules called EPA  and DHA .
Problem is, humans are very bad at this conversion – we only convert 3.8% of our ALA into EPA and 6% into DHA . No problem though, the practical solution is to eat sources of EPA and DHA which are the animal version of ALA. You get loads of EPA and DHA from eating all sorts of animals, in particular the kind that swim like salmon and sardines.
The technical definition of essential fats refers to those humans need to eat. One kind is the omega-6 (LA) and the other is the omega-3 (ALA).
Practically though, all you need to focus on is getting DHA and EPA by eating a variety of animal foods (algae is the notable exception because it’s a plant source of EPA and DHA )
Why do you need LA, EPA and DHA?
They do everything from keeping us sane, to creating as well as stopping inflammation. All very important things, clearly.
Inflammatory and anti-inflammatory action is such a fundamental process keeping us alive that any dysfunction in it is either shown to cause or contribute to most major diseases like cardiovascular disease  and diabetes . This doesn’t mean that taking more or less of these essentially fatty acids is a cure all, but it does mean that getting closer to the optimal omega-6-to-omega-3 ratio is of paramount importance.
These fats also ensure your cell membranes aren’t too rigid or fluid, which in science-speak translates to “lipids are the fundamental structural components of biological membranes” . Saying this is important is the understatement of the year.
What about other fats? Isn’t eating saturated fat bad?
In part 2 and beyond, we’ll go over the good sources of fats, like olive oil and pork that have lots of MUFAs (monounsaturated fats) as well as butter and coconut oil that have lots of SFAs (saturated fats). We’ll also make crystal clear why you should avoid foods high in vegetable oils and trans-fats (bad news, they’re in tons of processed food).
Till next time…try this: a tablespoon of quality cod-liver oil a few times a week. Let us know if you had the stomach for it.