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  • Writer's pictureRyan Allen

Distinguishing the different categories of fats

Fats constitute a major macronutrient category, playing several critical roles in our metabolism. They are fundamental to countless biological processes, yet it seems that for most of the public they remain poorly understood. This post is intended to give a brief overview of the various types of fats, which we will reference countless times in the future in discussing their implications for our health.

Figure 1: Triglyceride (TAG) synthesis from three fatty acid residues and glycerol. This is a condensation reaction that generates a water molecule for each fatty acid addition. (Image: Khan Academy)


The building blocks of fats are called fatty acids. These fatty acids can be added to glycerol for storage as triglycerides (aka triacylglycerols or TAGs; Figure 1), used as fuel sources, act as components of cell membranes, and so much more. The following are the three buckets that all fatty acids fall into:



Saturated fatty acids are long carbon chains connected entirely by single bonds. Because there are no double bonds in the molecule, each carbon is attached to the maximal number of hydrogen atoms that it can accommodate (Figure 2, top). You could say that, in this way, these fatty acids are “saturated” with hydrogens. They’re often found in solid form at room temperature and are commonly in animal products: butter, dairy, meat, and more. Though demonized for decades, there appears to be more nuance when it comes to understanding these molecules in our diet. Numerous studies, including a 350,000-subject meta-analysis, have concluded that there is insufficient evidence to suggest that dietary SFA intake is associated with increased coronary heart disease (CHD) or cardiovascular disease (CVD) risk. The current state of the evidence suggests that limiting SFA consumption can be beneficial if those calories are substituted for “healthier” unsaturated fats. If the alternative is something like refined carbohydrate, however, there likely will not be much (or any) benefit to reducing SFA intake.

Figure 2: Structure of saturated vs. unsaturated fatty acids. These molecules differ by the presence (or lack thereof) of a double bond between carbon atoms. The unsaturated fatty acid pictured, oleic acid, is a monounsaturated fatty acid (MUFA) as it only contains one double bond between carbons. (Image: Khan Academy)



While SFA carbon chains only consist of single bonds, monounsaturated fatty acids have one double bond (mono- meaning one) between a pair of their carbons. This double bond effectively takes away a couple hydrogen atoms from the carbons, making the molecule unsaturated. Believe it or not, this simple, seemingly small chemical distinction can result in a significant difference in the properties of these molecules. MUFAs are liquid at room temperature, and are predominantly found in olive oil and canola oil. Several foods are also rich in MUFAs, including avocados and certain nuts (almonds, hazelnuts, macadamias, etc.). These fats appear to be relatively good for your diet, with evidence demonstrating benefits to the lipid profile as well as glucose and insulin levels of the blood from MUFA consumption.



Polyunsaturated fats, as the name suggests, have more than one double bond in the carbon chain (poly- meaning multiple). So, multiple double bonds mean that there are multiple points of “desaturation” in the molecule. These molecules are not only liquid at room temperature, but typically liquid in the refrigerator as well. PUFAs are commonly found in certain vegetable oils, and they are the main form of fat found in seafood. For the most part, these are also thought of as “healthy fats,” with many studies finding similar cholesterol and glycemic benefits to MUFAs. The exact impact of PUFAs on the oxidation of LDL particles is still an active area of research, and it seems too early to conclude that they might contribute to atherosclerotic disease in this way.



One subgroup of PUFAs that many may have heard of is the omega-3 fatty acids. These are commonly found in seafood and have several suspected benefits to health and chronic disease risk reduction, including evidence supporting improved cardiovascular outcomes and positive effects on cognitive function. The three main ⍵-3FAs are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA can be converted to EPA and then DHA, but it is an essential fatty acid, meaning that our bodies cannot produce it de novo. Rather, it must be consumed, driving many (myself included) to supplement these molecules on top of regular consumption. However, routine inclusion of foods rich in ⍵-3FAs in one's diet is typically preferred to supplementation.



Lastly, the omega-6 fatty acids are another major subgroup of PUFAs. Mostly consumed in liquid vegetable oils as linoleic acid (LA), another essential fatty acid, ⍵-6FAs are predominantly converted to arachidonic acid (AA) inside the body. Though previously labeled as “bad” following observations of pro-inflammatory effects, ⍵-6FAs are seeing increasing evidence accumulating to demonstrate their importance, with a 2019 meta-analysis of almost 70,000 participants concluding that higher circulating LA levels were associated with lower CVD event risk.


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