Good Fats vs. Bad Fats

Last Update: May 15, 2023

For more than three decades, we have been told that fat is the enemy—that it’s responsible for both rising rates of heart disease and expanding waistlines.

As a result, in the ‘80s and ‘90s, grocery shelves were inundated with fat-free or low-fat versions of just about every food product available, convincing us to eradicate fat completely from our diets.

Then things began to change. One of the most important discoveries in recent years was a study of people living in Mediterranean regions that were seen as some of the healthiest, fittest, and longest-living people on the planet. The caveat: Their diets are full of fats—particularly high in olive oil and fish oil.

Around the same time, scientists started focusing on something called artificial trans fats, made by adding hydrogen to liquid vegetable oils to make them more solid. Though they’ve been hiding undetected in food since the dawn of America’s industrial food revolution, they’ve since been deemed unhealthy by healthcare professionals, linked to a host of problems including increased cholesterol levels, greater risk of stroke and heart attacks, and more susceptibility to type 2 diabetes. Subsequently many countries have started to ban trans fats, including the United States—the Food and Drug Administration (FDA) has ruled that manufacturers must stop using them by June 2018.

The latest research has further challenged traditional notions of how different types of fats affect bodies in surprising ways. As it turns out, some fats are essential to overall health and well-being, but it’s important to know which you should be eating and those that you should avoid at all costs.

Good fats

Despite all the commotion about dietary fat, there is a special class of “good fats” known collectively as unsaturated fats that include such items as olive oil and tuna. The reason these fats are so beneficial is because they include a special compound known as omega-3 fatty acids, which are associated with a myriad of health benefits and are wholeheartedly encouraged by the health community.

There are three forms of omega-3 fatty acids, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and alpha-linolenic acid (ALA). All are essential to human health, but unfortunately the human body cannot produce them. Therefore, they must be obtained supplementarily through diet.

Sources of omega-3 fatty acids

Luckily, an abundance of omega-3 fatty acids are available in a number of foods. The ALA type is primarily derived from plants and seeds. The foods with the highest sources of ALA are:

The EPA and DHA types are derived primarily from fish and other marine sources. Fish don’t produce omega-3 fatty acids either, but good amounts do accumulate in their bodies from regularly eating algae, krill, or smaller prey fish. DHA and EPA are found in the highest concentrations in the following sources:

  • European anchovies
  • Flatfish such as flounder, sole, fluke, turbot, and halibut
  • Herring
  • Pacific mackerel
  • Atlantic pollock
  • Wild salmon
  • Tuna
  • Atlantic sardines
  • Sea bass
  • Trout
  • Mussels
  • Oysters
  • Spiny lobsters
  • Seaweed
  • Kelp

How omega-3 fatty acids work

By now, it’s been well established that omega-3’s are a necessary part of human metabolism and development. DHA in particular is shown to be especially important in the neurological development of children. However, scientists are still out on how exactly these compounds produce the numerous health benefits associated with them.

The current theory is that omega-3 fatty acids by themselves don’t produce any appreciable health benefits. Rather, it’s thought that increased consumption of them restores the human body to a healthy ratio with another class of important dietary fats known as omega-6 fatty acids.

The human body also doesn’t produce omega-6’s, but they are found in abundance in vegetable oils and animal meats. Some scientists have estimated that human diets used to have an omega-6 to omega-3 ratio of 2:1, but have said it has increased anywhere from 10:1 to 20:1 in Western diets due to increased meat consumption.

What is understood is that both of these fatty acids are converted into different hormones that are responsible for a wide variety of bodily functions. Unfortunately, throwing off the ratio can also throw off the balance of necessary hormones in the body.

Benefits of omega-3’s

While most recognize that high cholesterol is bad for cardiovascular health, there is more to the equation than that number alone. There are actually two different types of cholesterol, also known as lipids: HDL (“good”) and LDL (“bad”). A high level of HDL in the bloodstream is actually quite beneficial, since it eradicates the LDL that can build up in the walls of blood vessels and lead to heart attacks and stroke. Eating more omega-3’s can help to encourage greater concentrations of HDL.

There is also a third lipid in the bloodstream: triglycerides. Increased levels of these have been associated with blocked arteries, heart disease, stroke, diabetes, and obesity. However, a diet supplemented with omega-3 fatty acids, especially EPA, has been shown to lower levels of blood triglycerides in both men and women.

Another significant contributing factor to heart disease is high blood pressure, which can damage artery walls and cause plaque to build up faster. There is a solution for this with omegas, too—DHA has been shown to effectively lower blood pressure.

Saturated fats

You may be surprised to find saturated fats on the good list, but recent studies have poked holes in the long-held belief that saturated fats are responsible for heart disease and obesity.

It all started in 2010 with a large study by the “American Journal of Clinical Nutrition” that found no evidence linking dietary saturated fat to increased risk of heart disease.

In 2014, another study in the “Annals of Internal Medicine” confirmed those findings, also securing no proof that limiting saturated fat consumption improves cardiovascular health.

Finally, in 2015, the “British Journal of Medicine” published the largest study to date also concluding that dietary saturated fats are not associated with heart health.

Further reports have actually shown the opposite to be true: Saturated fats that are composed mostly of medium-chain triglycerides, such as coconut oil, can have some pretty positive health benefits. Despite being comprised of 84 percent saturated fat, coconut oil has been shown to increase levels of HDL cholesterol in the bloodstream and possibly even reduce LDL cholesterol.

Such findings are proof that not all saturated fats deserve a reputation as an artery-clogging killer, and their elimination from our diets over the last four decades may have even exacerbated the rise in heart disease and obesity.

Of course, not all saturated fats are created equal and all should be consumed in moderation.

Bad fats

A subset of fats, known as trans fats, are now widely considered to be the worst kind you can consume, and should be avoided in every possible instance.

What are trans fats?

Trans fats are by and large a product of the industrial food process used by manufacturers across the country. Though there can be some trans fats naturally existing in animal products and byproducts, the most dangerous are the artificial trans fats (“hydrogenated and partially hydrogenated oils”) that are created by adding hydrogen to liquid vegetable oils to make them more solid. Doing so provides a product that is inexpensive, easy to use, and has a long shelf life. Trans fats are often used in fried and processed foods to give the final product a desirable taste and consistent texture.

However, the FDA has now ruled that hydrogenated (and partially hydrogenated) oils are no longer generally recognized as safe in American food products because of their devastating effects on human health.

The effects of trans fats

Trans fats have been proven to be extremely dangerous to human health. First and foremost, they raise levels of bad LDL cholesterol. In turn, this builds up plaque along the artery walls, essentially causing arteriosclerosis (or hardening of blood vessels), increased blood pressure, and increased risks of strokes and heart attacks.

The same “British Journal of Medicine” study that found dietary saturated fats were unrelated to heart disease and mortality turned the finger on trans fats as the actual culprit. It found that trans fats increased the risk of mortality by 34 percent as well as the risk of coronary heart disease by 21 percent and the risk of type 2 diabetes by 34 percent.

These findings are precisely why the FDA has ruled that trans fats must be removed from manufactured and commercial foods by 2018. However, a lot of food companies and restaurants have already voluntarily begun to eliminate trans fats from their products.

Still, companies can continue to use partially hydrogenated oils for the time being if they choose (and going forward if they have special FDA approval). In fact, if less than 0.5 grams of trans fats are included per serving, manufacturers can still label the content as zero grams on the nutrition label. To avoid trans fats completely, you should always be on the lookout for these ingredients:

  • Partially hydrogenated vegetable oil
  • Hydrogenated vegetable oil
  • Shortening
  • Margarine

There are also common foods that have trans fats, even though companies advertise zero grams on the label. They include:

  • Pie crusts
  • Cake mixes
  • Canned frostings
  • Non-dairy creamers
  • Microwaveable popcorn
  • Packaged cakes and cookies
  • Frozen dinners
  • Packaged pudding

A final word on good fats vs. bad fats

Most dietary fats are not as bad as we once thought them to be. Monounsaturated and polyunsaturated fats have long been associated with good health, and new research shows that even once dreaded saturated fats can have some amazing health benefits.

Fats are still high in calories, so like everything else, consume them in moderation. Here are some further tips from the American Heart Association on how to lower the intake of bad fats:

  • Reduce intake of trans fats and saturated fats to 5 to 6 percent of total daily calories.
  • Focus more on fruits, vegetables, whole grains, poultry, fish, and nuts. As well, limit sugary foods and calorie-laden beverages.
  • Cook with only unhydrogenated vegetable oils—olive oil is a great source of good fats.
  • Also look for processed foods made with unhydrogenated vegetable oils.
  • Use only soft margarine as a sub for butter and make sure it says zero grams of trans fat on the label.
  • Limit commercially fried foods and baked goods like doughnuts, cookies, crackers, muffins, pies, and cakes.

Illustration by Karley Koenig

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