Trans fat vs. Saturated fat: What is the difference and are they bad for you?

I often receive notes asking questions about dietary fats, like why is unsaturated fat healthier than saturated fat, and what is trans fat. Good questions, but to answer them I’ll have to first walk you through some biochemistry.

What are fatty acids and what do they do?

The basic unit of all dietary fats is fatty acid, composed of a chain of carbon atoms that have four bonding sites, right and left, up and down. The right and left bonds connect one carbon atom to the next like a string of pearls. The up and down bonds connect with hydrogen atoms.

When all up and down bonding sites are filled with hydrogen atoms, the fatty acid is considered to be saturated fat. If all the bonding sites are not occupied (saturated) with hydrogen, the fatty acid is unsaturated and there are two types. If only one site is not occupied it is a monounsaturated fat, whereas if multiple sites are not occupied it is a polyunsaturated fat.

Is saturated fat bad?

One reason saturated fat is considered to be unhealthy is that it can increase cholesterol production. Nearly all cholesterol in the bloodstream is manufactured in the liver. Cholesterol is very important to the body as a basic building block for several hormones, cell membranes, bile, etc. Unfortunately, when production is too great, excess cholesterol in the blood can attach to the walls of arteries, clogging them. This process is called atherosclerosis.

Therefore, when saturated fat increases cholesterol production, it may also be promoting atherosclerosis.

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What is atherosclerosis?

Here's how it works. The liver has receptors that report how much cholesterol is circulating. If there is too much cholesterol in the blood, the receptors tell the liver to take steps to reduce concentration. Sounds like a good system, and it is unless you consume too much-saturated fat because it interferes with the sensitivity of receptors. When this happens, cholesterol production goes up, increasing concentration in the blood. Let me add, ironically, blood cholesterol concentration typically is not elevated because of eating too much dietary cholesterol found in things like egg yolks, shrimp, beef, pork, cheese, butter, etc.

How to lower cholesterol

Other potential negative health effects associated with excess saturated fat intake include increased inflammation, some forms of cancer, and possible mental decline. But in fairness, I need to point out that controversy exists, and the source of saturated fat may dictate if it's unhealthy or not. The primary sources of saturated fat (fast food, fried food, sugary baked goods, processed meats, dairy products, etc.) are bad news. However, when the source is coconut or grass-fed meat, it may be a different story, but more long-term research is needed.

So, if you want to reduce the cholesterol concentration in your blood, cut saturated fat from your diet. Years ago, when I shifted to being a vegetarian and slashed my saturated fat intake (fast food, red meat, fatty dairy products, etc.), my serum cholesterol concentration was cut in half.

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What is trans fats?

As I have written many times, big business has a lot of influence over the foods we eat and how healthy or unhealthy they are, and so it is with saturated and unsaturated fats. From a business perspective, saturated fat is preferred because it is more robust and durable. If you deep fry in oil, you want the oil to hold up and be able to be used many times. That’s why when making French fries, a saturated fatty oil is preferred over an unsaturated one. In addition, the shelf life of saturated fat is much longer.

For more cost-cutting, businesses embraced the idea that you can change unsaturated fat into saturated fat through the process of hydrogenation (a chemical reaction that adds hydrogen to an unsaturated fat). Oils extracted from plants, such as soybeans, sunflowers, olives, etc. can be hydrogenated and provide a cheaper source of saturated fat for cooking. Unfortunately, it also contributed to a more serious health risk.

Artificially creating saturated fat through hydrogenation is unhealthy, but it's worse when the unsaturated fat is only partially hydrogenated converting it into trans fat. Partial hydrogenation means that instead of "adding" hydrogen to the point of full saturation (resulting in saturated fat), the hydrogen is "moved," or transferred (thus the term "trans" fat) from one place on the carbon chain to another.

As discussed above, saturated fat increases serum cholesterol. Trans fat does the same thing, but the increase in LDL (bad cholesterol) is greater, while HDL (good cholesterol) may decrease, making the critical LDL/HDL ratio worse. In addition, trans fat may have a greater impact on inflammation.

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The large-scale Nurses’ Health Study started in 1976 and is still ongoing with more than 275,000 participants found that those who consumed the greatest amount of trans fat in their diet had a 50% higher risk of a heart attack. Other studies also show a relationship between trans fat and decreased brain function and memory loss.

Are trans fats banned?

The FDA banned artificially produced trans fat in 2018. The result was to reduce trans fat, but not eliminate it entirely. For example, although a food label may claim "no trans fat," it is allowed to contain up to 0.5 grams per serving, and an average intake is about 5 grams per day. Thus, artificially produced trans fat is still lurking about in French fries and fried chicken, doughnuts, nondairy coffee creamer, stick margarine, refrigerated dough (biscuits and rolls), crackers, etc.

Trans fat also can occur naturally and is formed by bacteria in the stomach of some animals. Beef, lamb, and dairy products contain small amounts of trans fat, but it is a much smaller amount than that found when trans fat is artificially produced.

Trans fat destroys health as effectively as cigarette smoking, but it’s hard to avoid. Thankfully, we are consuming a lot less trans fat than we were in the past.

Reach Bryant Stamford, a professor of kinesiology and integrative physiology at Hanover College, at stamford@hanover.edu.

This article originally appeared on Louisville Courier Journal: Trans vs. saturated fats: are they bad for you? Here's what to know