Fatty acids are compounds that consist of long chains of carbon atoms attached to two hydrogens with a carboxylic acid (-COOH) at the end. There are various categories of fatty acids and different ways to categorize them.
Sometimes, in the sequence of hydrogen and carbon molecules, a hydrogen molecule is absent, and the carbon is forced to double bond to the next carbon. This distinction in structure leads to the three main types of fats: saturated, monounsaturated, and polyunsaturated. Saturated fatty acids (like palmitic and stearic acid) contain no carbon double bonds, monounsaturated (e.g., omega-9 fatty acids) have one, and polyunsaturated (aka, PUFAs like omega-3 and omega-6 fatty acids) have more than one.
So what’s with the numbers? Simply put, it’s a fancy, scientific way to identify the location of the first double bond in the sequence. This double bond placement gives the fatty acids their unique, magic touch (and names). There are various types–including omega-3, -6, and -9–classified by the spot that first double bond occurs.
Beyond this categorization, even more specificity exists. To get really into it, the main and most heavily researched types of omega-3s are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). The main omega-6s are linoleic acid (LA) and gamma-linolenic acid acid (GLA).
Of these five, by definition ALA and LA are the only “essential” fatty acids, meaning the body can’t produce them endogenously and we must consume them regularly. However, the body can synthesize longer-chain fatty acids (i.e., EPA, DHA, and GLA) from ALA and LA–but we’ll get to this process and its effectiveness (hint, it’s lacking) in a bit.