By Carl Hanson
March 02, 2016

For a while there, dietary fats were the villain, responsible for making us fat and ruining our health. After all, fat packs 9 calories per gram; protein and carbs, only 4 calories per gram. The math seemed pretty clear. Fats are fatty. Case closed. Cast 'em out of the kitchen!

By this clever new calculus, a bag of low-fat pretzels was inherently more healthful than a handful of nuts. And so in the early 1990s we turned our food focus from fats to carbohydrates. Sweet, sweet carbs. We loaded up on pastas and other refined carbs and reached for sugary snacks (hello, SnackWells). As long the label read "no fat" or "low fat," we figured we were golden. But we were only fooling ourselves. Rather than reduce obesity, our fat-free, carb-crazed days only helped turn it into an epidemic.

Photo by Meredith

Turns out, fats are friendly. Some fats, anyway. And so today, as we welcome fats back into the fold of respectable nutrients, let's take a closer look at the various fats; because it's true, not all fats are created equal.

Essentially, there are two groups of fats: Saturated fats and unsaturated fats.

Saturated Fats. Butter, lard, animal fat -- these are saturated fats. Why saturated? Because chemistry. Their fatty acids are densely packed together -- and saturated with hydrogen molecules. In practical terms, this means they're mostly solid at room temperature. More on saturated fats in a moment.

Photo by Meredith

Unsaturated Fats. Unsaturated fats, on the other hand, don't have that hydrogen saturation along the chains of fatty acids. So they typically remain liquid at room temperature. Think olive oil and other vegetable oils. The fats in nuts and avocados are also unsaturated.

Photo by Meredith

Among the family of unsaturated fats, omega-3 fatty acids stand tall. You've no doubt heard about the health benefits of omega-3 fatty acids. When people describe fatty fish like salmon as being healthful, they're usually talking about omega-3, an essential fatty acid that promotes healthy cardiovascular activity. Omega-3 may also protect against a host of health issues from obesity to sunburns. A 2005 study published by the Archives of Neurology claims that eating fish once a week may even slow the rate of cognitive decline. Nutrition Source at Harvard School of Public Health summed it up like this, "Omega-3 fats have been shown to help prevent heart disease and stroke, may help control lupus, eczema, and rheumatoid arthritis, and may play protective roles in cancer and other conditions."

The thing is, omega-3s are the only fatty acids our bodies don't manufacture. So we need to get these essential fats through the foods we eat. In addition to fish (like salmon, tuna, halibut, mackerel, sardines, and trout), omega-3 fatty acids are found in flax seeds, walnuts (and other nuts), and vegetable oils like olive oil and canola oil.

Grilled Salmon and Blueberry Sauce | Photo by Meredith

The Trouble with Trans Fats, A.K.A. Partially Hydrogenated Oils
Okay, now here's where things get a little strange. Trans fats are also unsaturated fats. Which sounds like a good thing. Only they're not naturally occurring unsaturated fats, like the healthy fats we find in nuts, vegetable oils, and avocados. Instead, trans fats are made through an industrial process (hydrogenation) that de-stabilizes the bonds between carbon atoms, causing them to flip into what's called a "trans" position. The bottom line: Trans fats have an unhealthy effect on blood cholesterol.

Here's why. There are two types of blood cholesterol: HDL and LDL. One good, one not-so-good. You can remember which is which with this simple mnemonic: "L" is for lousy; "H" is for happy. The lousy LDL cholesterol leads to plaque build-up in the arteries; happy HDL cholesterol, meanwhile, is like a vacuum, hoovering up the bits that can cause blockage.

Ideally, you want to eat fats that lower your LDL cholesterol and boost or at least don't diminish your HDL cholesterol. Unfortunately, trans fats are the dim bulbs of the fats world. They have it exactly backwards: Trans fats give a lift to the lousy cholesterol (LDL) and lower the good stuff (HDL). The result is an increased risk for heart disease.

Fortunately, trans fats are becoming increasingly unfashionable -- McDonald's, for example, hasn't fried with trans fats for over a decade. New York City, meanwhile, banned trans fats from restaurants back in 2007. And the FDA is working to ban man-made trans fats altogether from the US food supply. But until trans fats are gone completely, federal law requires that food producers list them on labels, so read nutrition labels on processed foods (like packaged crackers, cookies, and cakes). If you see trans fats on the label or "partially hydrogenated oil" in the list of ingredients, move right along.

Photo by Meredith

What about saturated fats and health? Yes, well, now we're entering into disputed territory. Experts disagree, and the science is still out. True, saturated fats have been shown to raise LDL cholesterol. But its effect on HDL cholesterol is more encouraging, if not necessarily offsetting: Saturated fat doesn't seem to lower the good cholesterol. So while saturated fat isn't exactly vindicated, it's maybe not the black hat-wearing villain either.

As The New York Times reported in 2014, an international team of scientists analyzed the existing data and "found no evidence that eating saturated fat increased heart attacks and other cardiac events."

However, a subsequent study came to a different conclusion. As Time magazine reported, this study suggested that data indicating no evidence for increased risk of heart disease could be flawed. Here's why: As we noted above, when people stop eating fat, they often replace the fat calories with calories from refined carbs, which is no improvement. In fact, people in the study who replaced the fat primarily with refined carbs ended up running risks of heart disease that were similar to the saturated fat eaters. Interestingly, people in this same study who replaced saturated fats with unsaturated fats and got their carbs from whole grains fared better than people who got their calories from refined carbs.'s complicated.

Meanwhile, new research shows that meat and milk from organically raised animals had "levels of omega-3 fatty acids, beneficial for lowering the risk of heart disease [that] were 50 percent higher" than meat and milk from conventionally raised animals. The reason for the elevated omega-3s in organically raised animals most likely is that the organically raised animals ate grass instead of grain -- and grass is much richer in omega-3s.

So what do the experts recommend? For the most part, the advice is simple: Completely avoid trans fats (there's just no point); limit saturated fat intake, particularly red meat (and eat grass-fed meat when you can); cook with and enjoy foods with healthy, satiating, unsaturated fats (the kind made in nature, not in a lab), including nuts, fatty fish, olive oil, and avocados.