Trans Fat vs. Saturated Fat: What’s the Difference?

Fat in the diet tends to get a bad rap. But the truth is, not all fats are not created equal.

There are those that do all sorts of good things for your heart health and those that can cause heart troubles when eaten in excess. And then there are the fats that offer so little nutrition and pose such a big health risk that the Food and Drug Administration (FDA) has asked food manufacturers to cut them out altogether.

Suffice it to say that fat is a somewhat complicated yet totally necessary nutrient.

“Fat isn’t all bad,” says Catherine Weichert Yeckel, MS, PhD, an assistant professor of clinical public health at the Yale University School of Public Health in New Haven, Connecticut. “We need fat because it’s part of all of our cell membranes, and getting a balance of different types of fat is important because it throws things toward a more calming state in the body.”

Ideally, your diet will primarily include healthy fats—the monounsaturated and polyunsaturated ones linked to better heart health. They’re found in vegetable oils like olive, canola, sunflower oils, nuts and seeds, avocados, and fish.

But there are two other types of fat you’ll cross at mealtime. Here’s what to know about saturated fat and trans fat, how they differ, and why one of them is best avoided.

(Related: 12 High-Fat Foods You Should Be Eating)

Trans fat vs. saturated fat

There are four main types of fat, and while nutrition experts recommend getting plenty of polyunsaturated and monounsaturated fats, that’s not the case for the other two types.

Trans fats and saturated fats don’t have the best reputations. They’re the so-called “bad fats” you’ve no doubt heard about. But while they’re both linked to health woes, they differ in some major ways.

Saturated fat has been demonized in the public health arena. It’s why for years health experts recommended a low-fat diet. After discovering a link between the fat and heart disease, they deemed fat in general something of a diet danger.

New research has modified that thinking (after all, mono- and polyunsaturated fats are healthy). Yes, a diet loaded with these fats is hard on your heart, but we do need some saturated fat. And even healthy foods like salmon and nuts contain some saturated fats, Yeckel says.

And on the flip side, even foods laden with saturated fats have some of the good stuff too. “Whole milk and butter have heart-healthy poly- and monounsaturated fats,” she points out.

Trans fat, on the other hand, is quite possibly the worst type of fat you can eat. It’s so bad for your health that it’s been pulled from food products (more on that later).

(Related: 38 Fat-Burning Foods to Help You Lose Weight)

What is saturated fat?

Compared with trans fats, saturated fat isn’t all that bad, Yeckel says.

“Saturated fat is a type of dietary fat that is typically solid at room temperature due to its chemical structure,” explains Arielle Leben, MS, a registered dietitian and certified diabetes nutritionist at New York University’s Langone Inflammatory Bowel Disease Center in New York City.

Chemically speaking, “these fat molecules do not contain any double bonds and are saturated with hydrogen atoms.”

Here’s a quick chemistry refresher: Fats are basically a chain of carbon atoms bonded to hydrogen atoms. They can have single bonds (saturated), a double bond (monounsaturated), or more than one double bond (polyunsaturated).

“Double bonds are good,” Yeckel says. “One characteristic is that they help make membranes more fluid so cells function more optimally.”

Put another way: “They bend in the right ways and the right times,” she says.

(Related: 6 Types of Heart Disease Doctors Need You to Know)

Saturated fat and your health

Saturated fat has been shown to raise low-density lipoprotein (LDL), commonly known as “bad” cholesterol. But it’s a bit more complicated than that, Leben says.

“Research published by the Journal of the American College of Cardiology in 2015 showed that when saturated fat was cut out of the diet and replaced with refined carbohydrates, no benefit was found,” she says. “However, when saturated fat was replaced with mono- or polyunsaturated fats, there was decreased risk of heart disease.”

So while it’s important to limit your saturated fat intake, what you choose to replace these calories with makes the biggest difference in improving your health, she explains.

“Healthy foods such as salmon, tahini, and nuts often contain some saturated fat but also far healthier mono- or polyunsaturated fats,” she says. “The health benefits of these foods outweigh the potential harm from smaller amounts of saturated fats they contain.”

So how much saturated fat should you get? The Canadian Food and Nutrition guide recommends aiming for a diet of 20 grams or less per day.

(Related: The Best Sources of Protein, According to the New Canada’s Food Guide)

How to eat less saturated fat

There are some easy ways to lower the amount of saturated fat in your diet without sacrificing taste, Yeckel adds.

Start by understanding which foods have saturated fat. They include:

• Red meat, such as beef, pork, and lamb
• Poultry with skin
• Lard
• High-fat dairy (butter, cream, cheese)
• Coconut oil
• Palm oil

For starters, switch to low-fat milk instead of whole milk, and trade butter in for olive oil.

“Instead of butter, smear avocado or olive oil on your toast,” she says. Both of these are rich in monounsaturated fatty acids.

Another easy swap? Don’t glob peanut butter on your sandwich. Instead, spread a light layer and then crunch walnuts on top for a healthy dose of omega-3 fatty acids.

These polyunsaturated fats can reduce the risk for cardiovascular disease, lower cholesterol and triglycerides, and lessen inflammation, among other health benefits. They’re found in a lot of fish, but there are plenty of omega-3 foods that aren’t fish.

Reading food labels carefully can help you make healthier choices. Fat is listed as “Total Fat” and also broken down so you can see how much is saturated.

Look at the recommended daily values, which are based on eating 2,000 calories a day, to keep saturated fats at less than 10 percent of total calories, according to the Academy of Nutrition and Dietetics.

(Related: 16 Things Doctors Do to Lower Their High Cholesterol)

What are trans fats?

Trans fats, also known as partially hydrogenated vegetable oil or trans fatty acids, are more harmful than saturated fats, Leben says.

Trans fats are a type of unsaturated fat, which come from natural or man-made sources. Naturally occurring trans fats are produced in the stomach of ruminant animals (such as cows and sheep) and can be found in certain meat and dairy products.

But most trans fat—and the type you always hear about—is industrial made. It’s created through a manufacturing process called hydrogenation. That’s when hydrogen is added to vegetable oil to convert it to a solid fat at room temperature.

“This process extends the shelf life of products,” says Leben.

Until recently, trans fats were commonly found in packaged, processed foods such as:

• Biscuits
• Frozen pizza
• Processed snack foods
• Cakes
• Doughnuts
• Pie crusts
• Stick margarine
• Shortening

(Related: This Nutrition Expert Is Encouraging You to Eat the Cookie)

Trans fat and your health

Hands down, trans fats are more harmful than saturated fats, Leben says.

Trans fat increases LDL cholesterol, lowers high-density lipoprotein (HDL, the “good” cholesterol), and has been associated with an increased risk of heart disease and stroke.

“Artificial trans fats, those created during hydrogenation, may increase risk of type 2 diabetes,” she says.

The National Academies of Sciences, Engineering, and Medicine recommends that trans fat intake be as low as possible. The FDA agrees.

In 2015, it stated that trans fats are no longer Generally Recognized as Safe (GRAS). On September 17, 2018, Canada banned the use of partially hydrogenated oils in foods, the main source of industrially produced trans fat. Products manufactured before this date could still be distributed to stores until January 2020 or, in some cases, 2021.

(Related: How to Choose the Best Food Habits for Your Health)

Trans fats in your food

Why are we still talking about trans fats if they’re banned? Foods containing less than 0.5 grams of trans fats per serving are labeled as having 0 grams on food labels.

Trans fats are also available in processed foods in other countries, and we don’t live or eat in silos, Yenkel says.

Plus, trans fats can be found in some natural sources, such as milk and meat. As for whether they’re as detrimental to your health as their man-made counterparts, the jury’s still out. But, says Yenkel, “these sources don’t seem to be as bad for you as the trans fats once found in processed foods.”

(Related: Why You Should Ditch the Diet Mentality and Aim for a Healthy Lifestyle)

Fats in your diet

Gone are the days of low-fat diet supremacy. In modern times, nutrition experts recognize the benefit (and necessity) of fat in the diet. The focus, instead, is on eating the right types of fat.

“We need to destigmatize fat in the diet, but we need to emphasize that processed foods and fried foods are bad,” Yenkel says.

Her advice? Avoid trans fats. Keep saturated fats to a minimum, and replace unhealthy fats with poly- and monounsaturated fats when you can.

Next: 13 Truths About Body Fat You Need to Know