How Do You Tell the Difference Between Trans Fat, Saturated and Unsaturated Fats?

When it comes to fat, there’s more than meets the eye.


Ah, fat — 30 years ago, when it came to healthy eating, it was Public Enemy No. 1. Back then, conventional wisdom suggested that getting too much “fat” in your food would make you gain weight, and cutting back on fatty meals would help you lose it. As a result, there was an anti-fat diet craze — fat-free butter, cookies, milk — and the thinking went that, as long as you bought low-fat or fatless foods, you could eat as much as you want as a result. This fact made the sugar lobby very happy, considering they paid for much of the research around “bad” fats. But that’s another story!

In the following 30 years, though, fat has undergone a bit of a renaissance — for example, sugar has largely supplanted it as the primary ingredient that causes us to gain weight, and it’s been discovered that fat isn’t all bad. In fact, of the three main types of fat — trans, saturated and unsaturated fat — one type, unsaturated fat, is generally agreed to be good for you!

So, given that some fat is healthy and some fat isn’t, is there an easy way to spot the difference between the mostly good (unsaturated fat), the maybe-possibly bad (saturated fat) and the ugly (trans fat)? Of course there is — you just need to use your eyes.

Unsaturated fats, i.e., the (mostly) healthy kind, have a molecular structure that includes double bonds between their fatty acids, which through the miracle of chemistry gives them a weaker molecular structure. That weak structure prevents unsaturated fat molecules from stacking nicely and turning into a solid, which means you can generally tell that a fat is an unsaturated fat if it’s liquid at room temperature — olive oil, peanut oil and other (non-hydrogenated, more on that in a second) vegetable oils are made up of primarily unsaturated fat.

Another way to tell if a fat is unsaturated is by checking where it comes from. Unsaturated fats are generally plant-based, with fish oil being the unsaturated (and very good for you) exception. But fats from other animals, like the kind you cut off your steak, are solid at room temperature, which should signal to you that it is saturated. For a long time, saturated fat — which has no double bonds in its molecular structure and is stacked with hydrogen atoms (thus saturated) — was thought to increase cholesterol and heart disease. But recent studies have found that link to be inconclusive. Basically, no one is really sure about saturated fat, so eat at your own risk!

The last variety of fat, trans fat, is most certainly not good for you. That’s because trans fats are created in a lab in order to transform (get it?) unsaturated vegetable oil into saturated, solid vegetable oil by artificially adding more hydrogen atoms, in order to increase shelf life and prevent spoilage. According to, trans fats are particularly bad because they lower good cholesterol while increasing bad cholesterol — which is really bad for your ticker.

Unfortunately, it’s not easy to tell trans fat apart from saturated and unsaturated fats with your eyes, namely because trans fat is rarely naturally occurring like saturated animal fat, or generally sold separately like liquid vegetable oil. Instead, it’s in the foods we eat, making it harder to spot. But you can tell which foods have them and which don’t if you know what to look for on the label. If a food includes “trans fat,” or “partially hydrogenated oil” in the ingredients list, then stay away.

Fat’s come a long way, but there’s still a stigma about this much-maligned ingredient — even against the healthy kind of fat. But if you’re still unsure, remember that if it’s liquid you’re probably okay (with notable exceptions), and if it’s solid, read the label. At the end of the day, though, the number one rule-of-thumb is, no matter what you put in your body, everything in moderation.