THE SKINNY ON FAT: The Complete Simpleton's Guide to Dietary Fat (PART 2)

THE SKINNY ON FAT: The Complete Simpleton's Guide to Dietary Fat (PART 2)

By Shane Robert

In part 1 of this series, we covered the basic biochemistry of fat, going into detail on what it is and what it does in the body. In this second part, we will cover the different types of fat and what role they play in positive or negative health outcomes. 

Types of Dietary Fat

From a 1,000-foot view, there are three types of fat into which all dietary fats fall: saturated fat, unsaturated fat, and trans fat — terms most people have likely heard of. Of course, as is often the case with biology and chemistry, things can get much more granular from there. If you refer back to part 1 of this series, you will recall that a fatty acid is a chain of carbon atoms with hydrogen atoms attached and a carboxylic acid group at one end. It is the types of chemical bonds that are created within these chains that determine what the type of fat it is.

1) Saturated Fat 

Saturated fat is a fatty acid chain with no double bonds between carbons, all the carbon-carbon bonds are single bonds, and every carbon atom is “saturated” with hydrogen. In other words, nearly every carbon has two hydrogens attached to it. This gives saturated fats a straight and rigid structure, which allows them to pack tightly and be solid at room temperature. Most people will recognize these fats as things like butter, lard, tallow, and red meat, though they do also come from plant sources such as coconut oil, palm oil and cocoa butter/dark chocolate.

For a long time, saturated fat has been considered the main “bad” fat, the one most closely associated with increased cholesterol levels, particularly the bad LDL cholesterol. More recent research has shown that it is quite a bit more nuanced than simply good or bad. There are different types of saturated fats that are determined by the carbon chain length and are aptly named, short-chain fatty acids (SCFAs), medium-chain triglycerides (MCTs), long-chain saturated fatty acids (LCSFAs), and finally very long chain fatty acids. Each grouping is further broken down into its specific acid, and each acid has different effects on the body.  

This table demonstrates that not all saturated fats cause an increase in LDL and/or cholesterol. Indeed, some are quite beneficial to overall health. Unfortunately, it is difficult to uncouple one type of saturated fat from another.For example, stearic acid, found in red meat and cocoa butter, does not raise LDL cholesterol (it may even lower it slightly) and is considered neutral for heart health. In contrast, palmitic acid, also found in red meat but highest in palm oil, is most associated with increased LDL cholesterol and possibly higher cardiovascular risk. They both contribute around 40-50% of the fatty acids found in red meat with the remainder of the fat being made of none-saturated sources (oleic acid, a heart healthy fat, is actually the single most abundant fat in red meat at around 40%).

As you can see, whether saturated fat is bad or not is complicated and a question that is still waiting to be answered.

2) Unsaturated Fat

Unsaturated fat is a fatty acid that contains one or more double bonds on its carbon chain. These double bonds between carbon atoms remove two hydrogen atoms from the chain when they bond together, making the chain become “unsaturated” with hydrogen atoms. The double bond causes a bend or kink in the fatty acid chain and prevents the molecules from packing tightly together, which is why unsaturated fats are typically liquid at room temperature. These fats are considered to be much more health promoting. They are generally regarded as heart-healthy, anti-inflammatory, and beneficial for cholesterol balance. Within the category of unsaturated fats, there are two subsets -monounsaturated fat (MUFAs) andpolyunsaturated fat (PUFAs).

Monounsaturated fats contain only one double bond (hence mono) in their carbon chain. The length of the chain, much like saturated fat, and the position of the double bond determines what type of MUFA it is. All of these fats are considered either omega-7 or omega-9 fats The ‘omega’ refers to the position of the first double bond from the methyl end (see part 1 if you forgot). The sources of monounsaturated fat are most closely associated with things like olive oil, any variety of nuts, and avocados, though they can occur in high amounts in animal fats as well (see saturated fat above for more details).

When it comes to this fat, oleic acid is the superstar, at least in terms of health research. It seems there is little that it doesn’t do, including improving HDL/LDL cholesterol ratio, reducing oxidative stress, supporting cell membrane fluidity, and it may even reduce inflammation and blood pressure. Palmitoleic acid, not to be confused with the saturated fat palmitic acid, is no slouch either. It’s currently being studied for its potential role in improving insulin sensitivity, reducing fatty liver, and supporting lipid metabolism

These are all great and wonderful things that we should want for our bodies. Definitely eat monounsaturated fats. As wonderful as they are, however, these omega-7 and omega-9 fatsare not essential, meaning our body can make them on its own, unlike omega-3 and omega-6 polyunsaturated fats. 

Polyunsaturated fats contain two or more double bonds on its carbon chain (hence poly). These fats are essential for health and come in different (main) types—omega-3 and omega-6. Omega-3 is named for the fact that the first double bond occurs on the 3rd carbon from the methyl end; omega-6 has the first double bond on the 6th carbon from the methyl end.

Omega-3

Omega-3 have been extensively studied and have been repeatedly shown to be incredibly beneficial to our health. Among other things, they reduce chronic inflammation, lower triglycerides, support brain and retina development. Current research is showing that they may reduce risk of heart disease, depression, and cognitive decline.

Omega-6

Despite what you may have heard, omega-6 PUFAs, as with omega-3, are essential fats, meaning our body can’t produce them on their own, and we must get them through our diets. They support immune function and cellular growth, and are needed for brain development and skin health. Excess arachidonic acid can promote inflammation and, if not balanced with omega-3s, unfortunately, it is typically overconsumed in most western diets. 

There is current internet controversy surrounding the role linoleic acid from vegetable and seed oils plays in inflammation. In the body, LA can be converted into AA through a series of enzymatic steps, albeit relatively inefficiently (typically <1% in humans). LA itself is not inherently inflammatory, but it serves as a precursor to AA. Excess linoleic acid, therefore, can promote inflammation indirectly by raising arachidonic acid levels. It doesn’t act anywhere as strongly or directly as AA itself. Whether it becomes a problem depends on your overall diet, particularly your intake of omega-3. Diets very high in LA and low in omega-3s (like many modern Western diets) are more likely to support a pro-inflammatory state. A healthy ratio of omega-6 to omega-3 is ideally 4:1 or lower, but modern Western diets often exceed 15:1. As of the time of this writing, it seems that the quality and source of your PUFAs matter more than sheer quantity.

Note: There are technically omega-7 and omega-9 PUFAs, however they are not a requirement in the diet, they likely can’t even be consumed through diet, and play a minimal significance in the body, so we won’t spend time on them.

3) Trans Fat

Last, and most certainly least, in our list of fat types are trans fats. Trans fats are technically a type of unsaturated fat with an unnatural structure that makes them harmful to health. Trans refers to the way hydrogen atoms attach around the carbon double bond in an unsaturated fatty acid. As was covered in the unsaturated fat section, unsaturated fats have removed two hydrogen atoms from the chain where their carbon atoms bond together, one from each carbon. This is known as the “cis” configuration and is what causes the bendiness in the molecule. In trans fats, the missing hydrogen atoms are added back at the point of the double bond, known as a "trans" configuration, making the molecule straighter, more like a saturated fat. This is called hydrogenation. 

The hydrogenation process occurs when hydrogen gas is bubbled through the oil at high temperature in the presence of a metal catalyst like nickel. The goal is to add hydrogen atoms to the double bonds, turning unsaturated fats into more saturated fat like solid and stable fats. A slight variation of this process is known as “partial hydrogenation,” which is still a trans fat but some of the double bonds are left unhydrogenated. Doing this makes the fats act more like saturated fats and give food a desirable texture, while being more shelf-stable than most saturated fats. This is why they were/are widely used in processed foods like margarine, baked goods, and fried foods.

Trans fats significantly increase the risk of heart disease by raising LDL (bad), lowering HDL, and increasing inflammation. They also increase heart disease, stroke, type 2 diabetes, and metabolic syndrome. Found mostly in processed foods, they are both easy and hard to avoid. Simply eliminating these foods from your diet greatly reduces exposure, but processed foods are often cheaper, more convenient, and have a longer shelf life than unprocessed options. They are also incredibly easy to overeat, which causes or exacerbates a whole host of other problems in the body.

Due to how harmful trans fats are to human health, many western countries (but not all) have banned them. I’ll let you guess which countries haven’t banned them. If you see any ingredient  label listing hydrogenated or partially hydrogenated, that’s trans fat, even if the trans fat on the nutrient label shows it as zero grams. Your best bet is to put it down and walk away.

NOTE: There are some naturally occurring trans fats that can be found in small amounts in meat and dairy from grazing animals (e.g. cows, sheep). These differ from man-made trans fats and don’t carry the same harmful effects. One of these fats, conjugated linoleic acid (CLA), may have neutral or even beneficial effects in small amounts. Since these fats occur at such low levels, even in meat and dairy heavy diets, they aren’t worth spending much time or concern on.

Not all fats are created equal. Lumping them together as simply “good” or “bad” does a disservice to the complex and nuanced role they play in human health. Saturated fats, long considered dietary villains, include a wide variety of subtypes with diverse effects, some bad, some neutral, some even beneficial. Unsaturated fats, particularly monounsaturated and omega-3 polyunsaturated fats, are widely recognized for their health promoting properties and essential roles in the body. Meanwhile, trans fats are unequivocally harmful and best avoided altogether. Understanding the chemistry behind these fats helps us make more informed decisions about what we eat. As is often with nutrition, context and quality matter just as much as quantity.

Part 3 will cover actually adding fat in our diets. How much, what kinds, when, etc.