For decades we were told that fat was a three-letter word and that its use should be minimized to help reduce the risk for cardiovascular disease. But like much that we have learned in the constantly evolving science of nutrition, not everything we thought was true was set in stone.

From the “low-fat” craze of the ‘80s and ‘90s to the renewed love for fat sparked by the Paleo movement, many people are still confused and unsure about fat; specifically, how to tell the good from the bad and how much to have.

Over the past decade and a half, researchers have conducted experiments to study the specific effect of altering quantity and/or type of dietary fat on risk for obesity, diabetes and all-cause mortality. They have also looked at epidemiological studies examining whole groups of people and their dietary patterns and its relationship to multiple health conditions. What they have found is quite interesting: Dietary fat is much more complicated than “include” or “avoid.” Fats can now be better classified into those that promote inflammation and illness and those that reduce inflammation and risk of disease.

The Good, the Bad and the Misunderstood

Fat is one of the three macronutrients (along with protein and carbohydrates) and contains nine calories per gram. Fat is essential in the diet as it helps the body absorb the fat-soluble vitamins (A, D, E, and K) and is a source of energy and a building block for hormones. It also helps keep skin and hair healthy, is a part of every cell membrane, and is important for the myelin sheaths around nerves.

The two best sources of dietary fats are monounsaturated fats (MUFAs) and omega-3 polyunsaturated fats (PUFAs). If you type “Mediterranean diet” into any search bar, you will come up with thousands of articles and studies about the health benefits of a Mediterranean diet, which happens to be higher in fat. A recent study published in the Annals of Internal Medicine looked at studies published between 1990 and April 2016. Researchers concluded that following a Mediterranean diet that is rich in plant-based foods (fruits, vegetables, nuts, seeds, whole grains, and legumes), moderate in red wine and dairy, and lower in meat and meat products was associated with lower risk of heart disease, stroke, diabetes and breast cancer. The Mediterranean diet is rich in both MUFAs and omega-3s.

Dietary sources of MUFAs include avocado, olive oil, almonds, cashews, Brazil nuts, sesame and pumpkin seeds, and peanuts. MUFAs have been shown to lower cholesterol levels and reduce both blood pressure and heart disease risk. The fat in oils, nuts and seeds can go rancid when exposed to heat and light, so it is best to keep these items in dark, cool places. Storing nuts and seeds in the refrigerator or freezer will extend their shelf life for months.

Omega-3 fats are one type of fat in the PUFA category. The other well-known PUFA is the omega-6 fats. There is a lot of controversy regarding omega-6 fats. Both omega-3s and 6s are essential fats, which means your body needs them but cannot produce them; the only source is from food. However, the typical diet is very high in omega 6s as it is found in corn, soy and cottonseed oils, as well as in most commercially prepared meals and packaged foods. Omega-6s have been linked to increased levels of inflammation in the body. The standard American diet can have a ratio of omega-6s to omega-3s of somewhere between 25:1 and 100:1, whereas the recommendation is to have a much smaller ratio of 2:1, and no more than 5:1.

Omega-3 fats are consistently viewed as anti-inflammatory and come from both animal and plant sources. Fatty fish, such as wild Alaskan salmon, sardines, herring, mackerel and tuna are among the best sources of the omega-3s EPA and DHA, which have been linked to heart, brain and eye health, as well as decreased joint pain. They may also be beneficial for depression and ADHD. Plant sources of omega-3s, found in flax, walnuts and seaweed, contain alpha-linolineic acid (ALA), which has to be converted in the body to EPA and DHA, but does so poorly. It is recommended to get at least 8 ounces of omega-3-rich fish per week and daily intake of plant sources.

Saturated fats are hard at room temperature and found in meat, dairy, coconut oil, palm oil, butter and lard. These foods have long been demonized for increasing cardiovascular risk because they were thought to increase total and LDL (“bad”) cholesterol. However, recent studies, such as this one published in the American Journal of Clinical Nutrition, have shown that there is no significant evidence for concluding that saturated fat increases the risk of cardiovascular disease. Major health organizations, such as the American Heart Association, for example, have been slow to come on board with removing the stigma associated with saturated fats.

One saturated fat that has been enjoying the limelight in the past few years is coconut oil. Solid below room temperature, this saturated fat is rich in lauric acid, which has been shown to increase the “good” HDL cholesterol and reduce the ratio of total cholesterol to HDL cholesterol, which reduces cardiovascular risk. Coconut oil has been lauded for improving both brain and gut health, and as a good source of energy due to its high concentration of medium-chain triglycerides (MCTs). MCTs are metabolized differently than other fats because they are sent directly to the liver where they are converted to usable energy rather than packaged into lipoproteins for storage.

While the consensus among health organizations that saturated fat is not the evil it was once believe to be, it is still recommended to get most fat from MUFAs and omega-3s.

The number-one fat that is universally agreed upon to avoid is trans fat. Although trans fats occur naturally in some foods, they are more commonly known as artificial fats produced through the process of hydrogenation. Trans fats were created by food manufacturers because they have a long shelf life and can prevent a food from going rancid quickly.

Although trans fats were a boon for food manufacturers, studies have shown that trans fats increase both total and LDL cholesterol, as well as decrease HDL, creating inflammation and increasing risk for heart disease, stroke, diabetes and other chronic diseases. Research from the Harvard School of Public Health and elsewhere indicates that trans fats can harm health in even small amounts: For every 2% of calories from trans fat consumed daily, the risk of heart disease rises by 23%.

Trans fats are found in vegetable shortening, pre-mixed products (cake and brownie mix), fried foods and prepackaged snack foods. As no amount is considered healthy, the best way to decrease this type of fat is to avoid products that have the words “Partially hydrogenated oil” on the label.

The Bottom Line

Fats play an important role in the diet. Although recommended levels range from 20-35% of total calories (or even higher), the most important factor is choosing a variety of healthy, quality fats, mostly plant-based, such as nuts and seeds. These fats, predominant in the Mediterranean diet, have been shown to decrease risk of cardiovascular disease, diabetes, and certain forms of cancer.