Dietary fat comes from both animal and plant foods.

Fats supply calories, help you absorb certain vitamins and provide essential nutrients that your body needs to function.

All foods that are rich in fat contain a mix of different fats — one of which is polyunsaturated fat.

Polyunsaturated fats are usually liquid at room temperature and are referred to as “oils.” They’re found mostly in fatty fish, plant-based oils, seeds and nuts.

This article examines food sources, health benefits and potential risks of polyunsaturated fats.

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There are two main types of fats — saturated and unsaturated.

A saturated fat has no double bonds in its chemical structure, whereas an unsaturated fat has one or more double bonds.

If a fat molecule has one double bond, it’s called a monounsaturated fat, but if it has more than one, it’s called a polyunsaturated fat.

Polyunsaturated fats — along with monounsaturated fats — are considered healthy fats, as they may reduce your risk of heart disease, especially when substituted for saturated fats (1, 2, 3, 4).

The two major classes of polyunsaturated fats are omega-3 and omega-6 fatty acids.

Both are essential fatty acids that your body needs for brain function and cell growth. Yet, your body cannot make essential fatty acids, so you must get them from your diet (5).

Summary Polyunsaturated fats are a type of healthy fat that includes omega-3 and omega-6 fatty acids, which are essential for brain function. You must obtain them from food, as your body cannot make them.

Dietary fats are a blend of saturated, monounsaturated and polyunsaturated fatty acids in different proportions.

For example, most of the fat in butter is saturated, but it also contains some mono- and polyunsaturated fats.

That said, some foods provide a higher percentage of omega-3 and omega-6 polyunsaturated fats than others. Here are several foods high in these essential fatty acids.

Omega-3 Fatty Acids

You can find omega-3s in pine nuts, walnuts, flax and sunflower seeds — but these give a less active form of the fat than fish do.

Fatty fish, such as salmon, boast the most omega-3s, whereas fish with a lower fat content, such as trout and bass, harbor lower levels.

The omega-3 content of 3 ounces (85 grams) of selected fish is (6):

  • Salmon: 1.8 grams
  • Herring: 1.7 grams
  • Sardines: 1.2 grams
  • Mackerel: 1 gram
  • Trout: 0.8 grams
  • Bass: 0.7 grams
  • Shrimp: 0.2 grams

Fish don’t produce omega-3 fatty acids on their own. Instead, they accumulate them by eating algae and small, microscopic organisms called plankton (7).

Omega-6 Fatty Acids

Plant-based oils are high in omega-6 fatty acids — with the exception of coconut and palm oil, which contain a high percentage of saturated fats and are solid at room temperature.

The oils highest in polyunsaturated fats include (8):

  • Safflower oil: 74.6%
  • Grapeseed oil: 69.9%
  • Flaxseed oil: 67.9%
  • Sunflower oil: 65.7%
  • Poppyseed oil: 62.4%
  • Soybean oil: 58.9%

These oils are liquid at room temperature because the double bonds allow the fat to bend and fold.

Oil-based condiments like mayonnaise and salad dressings, as well as margarines, are also high in omega-6 polyunsaturated fats (8).

Summary While flax seeds and walnuts contain omega-3s, the best source is fatty fish. Plant-based oils, which are liquid at room temperature, are the best sources of omega-6s.

As an essential component of your diet, polyunsaturated fats offer many impressive health benefits.

Much of these benefits are associated with the omega-3 fatty acids EPA and DHA.

May Reduce Age-Related Mental Decline

Omega-3 fatty acids are crucial for brain development and function.

Observational studies link low blood levels of DHA with mental decline in older adults (9, 10).

On the other hand, eating fish — which is high in DHA — may help prevent mental decline and related illnesses.

In a five-year study in over 200 older men, fish consumption was associated with less mental decline (11).

Another study in over 5,000 people noted that higher fish consumption was tied to a 60% lower risk of dementia and a 70% lower risk of Alzheimer’s disease over an average of two years (12).

Dementia is the loss of brain function that impairs a person's ability to think, remember or reason. Alzheimer’s disease is the most common cause of dementia among older adults (13).

While several meta-analyses have assessed how omega-3 fish oil supplements affect brain function in healthy older adults and those with Alzheimer’s disease, they have failed to find consistent results.

Some research suggests that omega-3s improve memory function in older adults — while other studies show no benefit (14, 15, 16).

May Improve Infant Development

Mothers who consume 8–12 ounces (227–340 grams) of fatty fish per week during pregnancy and breastfeeding may have healthier children (17).

In one study, the children of mothers who consumed fish more than twice per week performed higher on language and visual motor skills tests than children whose mothers did not regularly consume fish (18).

Another study noted that the children of mothers who ate 12 ounces (340 grams) of fish per week were less likely to have issues with behavioral, fine motor and communication skills (19).

However, fish oil supplements do not seem to give the same results. Randomized control studies have failed to find consistent benefits for infants whose mothers take omega-3 fish oil supplements (20, 21, 22).

For example, taking omega-3 supplements during pregnancy appears to provide few or no benefits for preventing preterm births, allergies in early childhood or children’s mental and visual development (23, 24, 25).

It’s recommended that pregnant or breastfeeding women consume weekly at least 8 but no more than 12 ounces (227 and 340 grams, respectively) of fish low in mercury, a heavy metal that can impair fetal development (17).

Pregnant women should limit or avoid fish with the highest mercury levels, including marlin, orange roughy, swordfish, tuna, king mackerel and shark (26).

May Promote Heart Health

Omega-3 polyunsaturated fats are renowned for their effects on heart health.

Studies in the 1960s and ’70s observed a decreased risk of dying from heart disease in populations that consumed fish (27, 28).

Later studies linked higher fish consumption and higher blood levels of omega-3s with a lower risk of heart disease and heart-related death (29, 30, 31, 32).

However, randomized control trials have found mixed results with omega-3 fish oil supplements (33, 34).

For example, in a study in over 12,500 people at risk of heart disease, supplementing with omega-3s for five years did not reduce their risk of either the disease or heart-related death (35).

Similarly, a review of 10 studies in nearly 78,000 people prone to heart disease saw no benefit of omega-3 supplements on risk of heart attack, stroke or any other related trauma (36).

However, fish oil supplements have proved effective at lowering triglycerides, a type of fat which — when elevated — increases your risk of heart disease and stroke (37).

Summary Omega-3 polyunsaturated fats may boost heart health, promote healthy infant development and prevent mental decline in older adults.

Moderation is key when it comes to nutrition.

The same goes for polyunsaturated fats — as consuming too much can pose health risks.

Increased Inflammation

Omega-3 and omega-6 polyunsaturated fatty acids play important roles in inflammation. In general, omega-3s are anti-inflammatory while omega-6s are pro-inflammatory (38).

Though inflammation can help you fight infections and heal injuries, chronic inflammation is at the root of several illnesses, such as obesity, diabetes and heart disease (39, 40).

Consuming too many omega-6s in relation to omega-3s is thought to promote inflammation and contribute to poor health (41).

As a result of excess omega-6-rich vegetable oils in the Western diet, experts agree that people get plenty of omega-6 fatty acids and not enough omega-3s (42, 43).

The Western diet’s high omega-6-to-omega-3 ratio is one reason it’s associated with many inflammatory conditions — especially heart disease (41).

Concentrated Calories

All fats, including polyunsaturated fats, contain 9 calories per gram — more than twice the calories found in carbs or protein.

Therefore, the calories from polyunsaturated fats can add up quickly. If you’re not careful, you might exceed your calorie needs.

As such, if you intend to consume more polyunsaturated-rich foods, it’s recommended that you remove other calories elsewhere — rather than simply adding polyunsaturated fats to your diet (17).

For example, if you wanted to replace some of your saturated fats with polyunsaturated fats, you could cook and bake with liquid oils instead of butter, lard or shortening, which are high in saturated fats.

Improper Storage and Use in Cooking

Polyunsaturated fats spoil more quickly than other fats because of their multiple double bonds (44).

Therefore, you should store these oils in a cool, dark place before opening, after which you should keep them in the refrigerator (45, 46, 47).

Polyunsaturated fats also have a lower smoke point, which is the temperature at which an oil starts to smoke (48).

When oil smokes, its fat breaks down and produces harmful substances, some of which have been linked to cancer and neurodegenerative diseases in animal studies (49, 50, 51).

Summary A low omega-3-to-omega-6 fatty acid intake may cause inflammation, an underlying factor for many diseases. You should also take care to not overconsume polyunsaturated fats or improperly store or heat them.

Omega-3 and omega-6 fatty acids are two main types of polyunsaturated fats.

Fatty fish is particularly rich in omega-3s, while plant-based oils made from safflower or flax and grape seeds are good sources of omega-6s.

Especially omega-3 may promote heart health, healthy infant development and brain function in older adults.

Still, there are certain risks associated with consuming copious amounts or improper storage and cooking.

Nonetheless, you should aim to make polyunsaturated fats — especially omega-3s — a healthy part of your diet.