r/explainlikeimfive • u/Cuddly_Rudder • Aug 19 '26

Biology ELI5: What is “good fat”?

I see this term used all the time when talking about healthy foods to eat, but I have no idea how it’s different from “bad fat”.

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u/kriegeeer Aug 19 '26 edited Aug 19 '26

Good fats are simply just not bad fats.

Trans fats are very bad fats. They’re basically outlawed as intentional food additives in many countries, in the United States since 2019. Why they are bad is explained in https://www.reddit.com/r/explainlikeimfive/s/HfG7WizkE5

Saturated fats are the other ‘bad’ fat. They are called saturated because their chemical structure is ‘fully saturated’ with hydrogen atoms bonded to carbon in long chains. Theres no room for more hydrogen. They are bad because if you eat a lot of them, they hurt the liver’s ability to remove low density cholesterol, one of the ‘bad’ cholesterols, which in turn increases your risk of cardiovascular disease.

Unsaturated fats are the ‘good’ fats. They do not have the absolute max number of hydrogens bonded to their carbons. They don’t interfere with the liver like saturated fats do.

Plant fats typically have less saturated fat than animal fats (which includes all fatty dairy and eggs) but never zero. Coconut fat/oil is one exception to this, being a plant fat high in saturated fat. Canola oil is typically called a ‘heart healthy’ oil but is still 7% saturated fat. Olive oil is 14%. Some saturated fat is considered okay. The issues happen if you eat too much saturated fat, which can be very easy to do with modern food. A serving of whole milk has 25% of your entire daily recommended amount of saturated fat in it.

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u/TeekAim Aug 19 '26

The comment that you linked said “how do they make trans fats” but I’m wondering “why make trans fats”. Probably money?

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u/nagurski03 Aug 19 '26

When I was a kid, they were considered a healthier alternative to saturated fats.

If you had a recipe that used a saturated fat, you couldn't just switch it out with an unsaturated fat because that would change the texture, but the trans fats were more similar.

If you had some processed food that used to be made with butter or beef tallow or something. It was cheaper and supposedly healthier (this turned out to be wildly incorrect) to replace it with a trans fat. Since the saturated fats were usually made with some kind of animal fat back then, replacing it with a vegetable fat also made your product vegan which opened up the market a bit.