The False Dichotomy of Fats

How we’ve bastardized our understanding of the physiology of lipids for the sake of simplicity

Stephen Decker
6 min readMar 12, 2019

The study and understanding of dietary fatty acids in human health and disease is of undeniable importance. Fats provide humans with a crucial form of energy and mode of transporting numerous nutrients through the body, rendering fats an essential nutrient — we need to eat them to survive.

The conventional categorization of fatty acids distributes these vital nutrients into two major groups — saturated and unsaturated. Saturated fats are long chains of single-bonded carbons due to each carbon in the chain being fully saturated with hydrogens which gives them the characteristic of being solid at room temperature. Unsaturated fats, on the other hand, contain at least one double-bond carbon chain, rendering them liquid at room temperature. Furthermore, the dogma surrounding these two categories of fatty acids states simply that unsaturated fats are beneficial for health, while saturated fats are detrimental for health and should be avoided.

Note: I’m not going to discuss trans fats in this post, even though they are found in small amounts of some natural foods and are a category of fats, they serve a different role.

Now, there are several inherent issues within this paradigm. First off, the foods that we eat rarely contain isolated species of fatty acids. Coconut oil, for example, is usually viewed as a source of dietary saturated fat, but actually contains a fair amount of unsaturated fats as well (the same goes for butter and lard, as well as sources of unsaturated fats like olive oil). Secondly, this assumes that all saturated and unsaturated fats create the same (or at least similar) physiological responses in their respective categories. In other words, the saturated fats in coconut are the same as the ones in butter. Likewise, the unsaturated fats in olive oil are the same in canola oil. Lastly, and most importantly, this assumes that the specific species of fatty acid — as determined by the number of carbons in the fatty chain — do not matter. This, IMO, is the biggest problem in this topic and will be the bulk of this post.

https://www.palmoilandfood.eu/en/fatty-acid-composition

To address my first point, the above graphic clearly depicts the point I’m making — no food source contains saturated or unsaturated fats in isolation. In fact, lard (which has been ostracised for decades) is about a split 50/50 content of saturated and unsaturated fats. Palm oil, derived from the palm tree making it a vegetable oil, has almost the same composition as lard. The reason I point this out is to bring up the simple fact that isolation of dietary fat species is extremely rare and unnatural. My hunch is that overall, the vast majority of people eat foods with a mix of fats rather than the single fats that are proclaimed in the epidemiology research.

I will address my last two points by starting off by saying…

Not all fats are created equal, even within the dichotomy of saturated and unsaturated fats.

Consider the following:

While research has gotten into this poor habit of simplifying fats into saturated and unsaturated categories, the true physiological function of a particular fatty acid is determined by its chemical structure. To my point, a 4-carbon fat (butyric acid; produced by gut bacteria when digesting fiber) acts differently than a 12-carbon fat (lauric acid; the primary component of coconut oil) which acts differently than a 16-carbon fat (palmitic acid; the primary form of storage fat found in humans) which acts different than an 18-carbon fat (stearic acid; a major fat from animals). To make things more complicated, the formation of the bonds in the structure (i.e. whether or not they have a double or single bond, and where that bond is located) also makes a difference. Palmitoleic acid, for example, is an unsaturated fatty acid with a very different physiological role than that of it’s saturated counterpart, palmitic acid. On a similar note, linoleic acid and linolenic acid are both unsaturated forms of stearic acid.

A simple example of the crucial roles of saturated fats (and their physiological complexity) would be the role that butyric acid plays in the human health. Butyric acid (a saturated fat) is a short-chain fatty acid that is primarily produced in the gut by our gut microbiota. Interestingly, butyric acid is mostly produced via the breakdown of soluble dietary fiber. The breakdown of these fibrous materials by the gut results in the release of butyric acid (or it’s conjugate base, butyrate) into the bloodstream. The release of butyrate (as well as supplementation with this fat) has been shown to have a wide range of benefits: from suppression of appetite via Peptide YY to a decrease in atherosclerotic plaques and more.

Paparo et al., 2017

Compare this with another saturated fat, lauric acid, which also has many potential benefits and is thought to be the driver of the many benefits of coconut oil. Contrary to the erroneous belief by some based on the classification of lauric acid as a saturated fat, lauric acid does not appear to be easily stored in human fat tissue, making it more prone to be metabolized for energy (which is why it’s used to induce ketogenesis). Moreso, because it becomes metabolized more easily, lauric acid is less likely to be converted to lipids that are associated with various diseases and dysfunction.

There are possible harms from saturated fats, too. Palmitic acid (the most abundant fat in humans) can result in the production and accumulation of ceramides, which are thought to be directly related to insulin resistance and obesity (I’ve written on this in the past).

Likewise, unsaturated fats are commonly known to be beneficial for cardiovascular health and play an important role in maintaining good function of a number of organs. However, the oxidation of unsaturated fatty acids can be quite problematic. There is a growing interest in the investigation of the role of unsaturated fatty acids (especially omega-6 fatty acids) in the pathogenesis of heart disease due to the increased likelihood of these fats becoming oxidized in both cooking and normal physiological processes.

Ng et al., 2014

In fact, the relationship between cooking vegetable oils (high in unsaturated fatty acids) and increases in cardiovascular disease risk seems to be quite an interesting story. While the details and mechanisms are still being elucidated, it appears that the heating of vegetable oils creates thermal-oxidized fatty acids. When these thermal-oxidized fats are ingested, they increase the amounts of oxidative stress and potentially contribute to the accumulation of oxidized LDL particles in the blood, which can then exacerbate the atherogenic process and contribute to CVD.

Now, I’m not out to demonize a particular class of fatty acids. The point of this article is to fully express my frustration with those who wish to bring out erroneous beliefs about the roles of fats in health and disease. The oversimplification of the physiological role of fats has created this grand stigma against the consumption of saturated fats — a belief that is completely unsupported by the literature. Are there harms of consuming some species of saturated fats? Yes. Are there benefits of consuming some species of saturated fats? Yes. Are these caveats the same for unsaturated fats? Yes.

Physiology is complex and confusing, and that’s ok.

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Stephen Decker
Stephen Decker

Written by Stephen Decker

Ph.D. student at UMass Amherst. A lifelong student in health, fitness, philosophy, and all things under the sun. Love ideas, but love sharing ideas more.

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