At some point in our lives, we’ve all heard that eating fat is bad for us. But the truth is more complex. The way we think about fat and how we eat it has evolved over time.

After years of research, we now know that fat is actually an essential part of a heart healthy diet. Your body needs healthy fats for multiple processes – everything from cell production to vitamin absorption to body heat retention.

But not all fats are created equal, and only some types of fat are healthy. There are three main types of dietary fats: unsaturated fats, saturated fats and trans fats, and each can impact your health in a different way. Below, we’ll discuss the good fats, the bad fats and everything in between.

If fats are good for us, why did they become “bad”?

In the early 1960s, when Americans were consuming 40-45% of their daily calories in the form of fat, heart disease was one of the leading causes of death in the country. As the link between disease and nutrition became clearer, health experts realized that a change needed to be made in the American diet.

They placed the blame on fat and urged the public to eat less of it, so people began replacing the fat in their diets with more carbs and sugar. In the 1980s, fat-free foods – free of fat, but full of processed sugar and chemicals – hit the grocery store shelves and just as quickly flew off them. Experts saw the rates of cardiovascular disease fall, but rates of obesity and diabetes began to climb.

A key fact had been lost in communication with the public. The message became all kinds of fat are unhealthy, when the truth is that only some are unhealthy, and moderation is key.

Why our bodies need (good) fats

Maybe you’re thinking fats just aren’t worth the trouble. Why not avoid eating them entirely? Well, you’d be missing out on all the ways fats help your body function at its best. Here’s how dietary fats work for you:

  • Building blocks: Fats are a source of essential fatty acids, which your body needs in order to make and maintain healthy cells. Think of fats like building blocks that your body uses to create strong organ tissue.
  • Vitamin absorption: Fat helps your body absorb vitamins, specifically vitamin A, vitamin D, vitamin E and vitamin K. These are “fat-soluble” vitamins, meaning they can only be broken down and absorbed in your body with the help of fats.
  • Energy boost: Fats are full of calories. They contain more than double the number of calories per gram compared to carbohydrates and protein. This makes fats an excellent source of energy, and because your body burns through fats slowly, the energy they supply is sustained and steady.
  • Body fat: Any fat that your body doesn’t use right away is converted into body fat, which helps your body retain heat and forms a protective layer around your organs, like insulation. Body fat also serves as a reserve store of energy, which your body draws on when it runs out of calories to burn.
  • Feeling full: Fats are dense and complex nutrients, so your body has to work a little harder to break them down. They spend more time in your digestive system, which helps you feel fuller longer.

What happens when we don’t eat enough healthy fats?

A shortage of fats in your diet can have far-reaching effects on your health:

  • Persistent hunger: Fat is one of the most calorie-dense nutrients out there. Without it, you may find yourself eating more calories and still feeling hungry.
  • Mental fog: The human brain is almost 60% fat. The essential fatty acids from fat help your brain stay healthy and sharp.
  • Dry skin and hair: Your skin and hair need the oils from fats to stay healthy and moisturized from the inside out.
  • Painful joints: Your joints need the oils from fats to stay healthy, lubricated and flexible.
  • Feeling cold: Your body needs fat to regulate its temperature, and a layer of body fat helps you generate and hold onto your body heat.

Why are some fats unhealthy for us?

To reap the benefits of fat, it’s important to stick to the ones we know are healthy for us. So, why are some fats healthy while others are considered bad fats? It comes down to cholesterol.

Unhealthy fats increase the level of LDL cholesterol in your body, which is a type of harmful cholesterol that builds up on the walls of your veins and arteries, contributing to heart disease and stroke. Healthy fats increase your level of HDL cholesterol (sometimes called “good cholesterol”), which absorbs LDL and takes it to the liver, where it’s filtered from your body.

Types of fats

The good fats: Unsaturated fats

By lowering the level of harmful cholesterol in your body, unsaturated fats can decrease your risk for heart disease and stroke. They also provide important nutrients that your body can’t make on its own, like omega-3 and omega-6 fatty acids, as well as the antioxidant vitamin E.

But what are unsaturated fats exactly? There are two types of unsaturated fats: monounsaturated and polyunsaturated. While they’re similar, they have different chemical compositions and are found in higher amounts in different foods.

Monounsaturated fats

Foods that are a good source of monounsaturated fats include:

  • Plant-based oils like olive oil, canola oil and sesame oil
  • Avocado
  • Peanut butter
  • Nuts

Polyunsaturated fats

Foods that are a good source of polyunsaturated fats include:

  • Fish like salmon, whitefish, sardines, herring and anchovies
  • Plant-based oils like soybean oil, corn oil and sunflower oil
  • Walnuts
  • Sunflower seeds and flaxseeds
  • Tofu

The not-so-healthy fats: Saturated fats

Saturated fats can be harmful to our health if we eat too much of them. In fact, the American Heart Association (AHA) recommends limiting the amount of saturated fats in your diet because they can increase the level of bad cholesterol in your body.

While your body takes longer to digest all fats, saturated fats, as well as trans fats, are particularly hard on your digestive system. If you’ve ever felt sleepy after eating a big, greasy meal, it’s because your body is working hard to break down these unhealthier fats.

What are saturated fats?

Saturated fats are typically found in animal products, like dairy and red meat, and tropical oils. Saturated fats are liquid when hot, but begin to solidify at room temperature – think bacon grease – so they are sometimes called “solid fats.”

Foods with a high amount of saturated fats include:

  • Red meat like beef, pork and lamb
  • Dark-meat poultry (especially with skin)
  • Butter
  • Cheese
  • Ice cream
  • Coconut oil

The bad fats: Trans fats

Trans fats are the least healthy fats because they raise bad cholesterol and lower good cholesterol, increasing risk of heart disease and stroke. Trans fats can also contribute to type 2 diabetes. Unlike the other fats we’ve discussed, trans fats have no nutritional value.

What are trans fats?

Most of the trans fats that we find in our food are artificially produced through a process called hydrogenation, in which hydrogen is added to vegetable oil. It makes an oil that would normally be liquid at room temperature, solid instead. That’s why trans fats sometimes appear on ingredients lists as partially hydrogenated oil.

A small amount of trans fats can be found in meat and dairy products that come from hooved, grazing animals like cows, as trans fats occur naturally in their digestive systems. It’s unclear whether these natural trans fats have the same harmful effects to our health as the artificial kind.

Trans fats used to be added to fried, packaged or processed foods because of their ability to increase shelf life. In 2015, the US Food and Drug Administration (FDA) banned the addition of artificial trans fats to food due to their harmful health effects. However, certain foods may still contain small amounts of these unhealthy fats, including:

  • Nondairy creamers
  • Microwave popcorn
  • Frozen pizza
  • Frozen yogurt and milkshakes
  • Shortening and solid margarine
  • Commercial baked goods like cookies, pies, donuts, cakes and cake mixes
  • Fast food

How much fat should I eat per day?

It’s all about moderation. Fat is more calorie-dense than any other nutrient, which is what makes you feel fuller longer. But this can also make it easy to overindulge.

Keep in mind that eating too much of any kind of fat, healthy or unhealthy, can cause weight gain. Unsaturated fat, with all its benefits, should not be an addition to your diet, but instead a replacement for saturated and trans fats.

The AHA recommends that no more than 25-30% of your daily calories come from fat; less than 10% from saturated fats, and the rest from unsaturated fats.

Tips for balancing the fats in your diet

AHA guidelines encourage limiting saturated fats, avoiding trans fats entirely and including unsaturated fats in moderation. Following these guidelines can improve your heart health while also decreasing your risk of stroke and diabetes. Here are some tips for putting those guidelines into action:

  • Incorporate more fruits, vegetables, whole grains, nuts, fish and poultry (without the skin) into your daily meals. The Mediterranean diet is a perfect example of a diet rich in healthy fats.
  • Use plant-based oils and sauté food in olive oil instead of butter.
  • Save red meat for special occasions and enjoy ice cream and cheese sparingly.
  • Read the nutrition facts and ingredients lists on products to steer clear of trans fats and its alter ego, partially hydrogenated oil.
  • Try to limit your consumption of processed and fast foods.

Fitting fats into a healthy lifestyle

With so many different diets and nutrition advice out there, it can be a confusing and often frustrating task to figure out what works for you. As we discussed above, a diet with too much fat is unhealthy, but so is a diet with no fat at all. Finding a balance can help you create healthy eating habits that last.

If you have questions or concerns about fats in your diet, talking to your primary care doctor or clinician is a great place to start. They can help you come up with a plan to balance your diet and exercise for long-term health. They can also help connect you with one of our knowledgeable dietitians for additional nutrition expertise if needed.