By Dr. Ruairi Robertson

Omega-3, omega-6 and omega-9 fatty acids are all important dietary fats.

Interestingly, each one has a number of health benefits for your body.

However, it's important to get the right balance of omega-3, -6 and -9 fatty acids in your diet. An imbalance may contribute to a number of chronic diseases.

Here is a guide to omega-3, -6 and -9 fatty acids, including what they are, why you need them and where you can get them.

What Are Omega-3 Fatty Acids?

Omega-3 fatty acids are polyunsaturated fats, a type of fat your body can't make.

Their name comes from their chemical structure, as "poly" means many and "unsaturated" refers to double bonds. Together they mean that omega-3 fatty acids have many double bonds.

"Omega-3" refers to the position of the final double bond in the chemical structure, which is three carbon atoms from the "omega" or tail end of the molecular chain.

Since the human body can't produce omega-3s, these fats are referred to as "essential fats," meaning that you have to get them from your diet.

The World Health Organization (WHO) recommends eating at least two portions of oily fish per week, which is rich in the omega-3s EPA and DHA (1).

There are many types of omega-3 fats, which differ based on their chemical shape and size. Here are the three most common:

• Eicosapentaenoic acid (EPA): This 20-carbon fatty acid's main function is to produce chemicals called eicosanoids, which help reduce inflammation. EPA also helps reduce symptoms of depression (2, 3).

• Docosahexaenoic acid (DHA): A 22-carbon fatty acid, DHA makes up about 8 percent of brain weight and is extremely important for normal brain development and function (4).

• Alpha-linolenic acid (ALA): This 18-carbon fatty acid can be converted into EPA and DHA, although the process is not very efficient. ALA is mainly used by the body for energy (5).

Omega-3 fats are a crucial part of human cell membranes. They also have a number of other important functions, including:

• Improving heart health: Omega-3 fatty acids can increase "good" HDL cholesterol. They can also reduce triglycerides, blood pressure and the formation of arterial plaques (6, 7, 8, 9, 10).

• Supporting mental health: Taking omega-3s can reduce symptoms of depression, schizophrenia and bipolar disorder. It can also reduce the risk of psychotic disorders for those who are at risk (11, 12, 13, 14, 15).

• Reducing weight and waist size: Omega-3 fats play an important role in weight management and can help reduce waist circumference (16, 17).

• Decreasing liver fat: Consuming omega-3s in your diet can help decrease the amount of fat in your liver (18, 19, 20).

• Supporting infant brain development: Omega-3s are extremely important for brain development in babies (4, 21).

• Fighting inflammation: Omega-3 fats are anti-inflammatory, meaning they can reduce the inflammation in your body that can contribute to a number of chronic diseases (22, 23, 24).

• Preventing dementia: People who eat more fish, which is high in omega-3 fats, tend to have a slower decline in brain function in old age. Omega-3s may also help improve memory in older people (25, 26).

• Promoting bone health: People with higher omega-3 intake and blood levels tend to have better bone mineral density (27, 28).

• Preventing asthma: Omega-3 intake can help reduce symptoms of asthma, especially in early life (29, 30, 31).

Unfortunately, the Western diet does not contain enough omega-3s. A deficiency may contribute to chronic diseases like obesity, diabetes and heart disease (32).

Summary: Omega-3 fats are essential fats that you must get from your diet. They have important benefits for your heart, brain and metabolism.

What Are Omega-6 Fatty Acids?

Like omega-3 fatty acids, omega-6 fatty acids are polyunsaturated fatty acids.

The only difference is that the last double bond is six carbons from the omega end of the fatty acid molecule.

Omega-6 fatty acids are also essential, so you need to obtain them from your diet.

These fats are primarily used for energy. The most common omega-6 fat is linoleic acid, which can be converted into longer omega-6 fats such as arachidonic acid (ARA) (33).

Like EPA, ARA is used to produce eicosanoids. However, the eicosanoids produced by ARA are more pro-inflammatory (34, 35).

Pro-inflammatory eicosanoids are important chemicals in the immune system. However, when too many of them are produced, they can increase inflammation and inflammatory disease (36).

Although omega-6 fats are essential, the modern Western diet contains far more omega-6 fatty acids than necessary (37).

The recommended ratio of omega-6 to omega-3 fatty acids in the diet is 4:1 or less. However, the Western diet has a ratio between 10:1 and 50:1.

Therefore, although omega-6 fats are essential in the right quantities, most people in the developed world should aim to reduce their omega-6 intake (37).

Nevertheless, some omega-6 fatty acids have shown benefits in treating symptoms of chronic disease.

Gamma-linolenic acid (GLA) is an omega-6 fatty acid found in certain oils, such as evening primrose oil and borage oil. When consumed, much of it is converted to another fatty acid called dihomo-gamma-linolenic acid (DGLA).

One study showed that taking a high dose of GLA supplements significantly reduced a number of symptoms of rheumatoid arthritis (38).

Another interesting study found that taking GLA supplements in addition to a breast cancer drug was more effective at treating breast cancer than the drug alone (39).

Conjugated linoleic acid (CLA) is another form of omega-6 fat that has some health benefits. For example, one large study found that taking 3.2 grams of CLA supplements per day effectively reduced body fat mass in humans (40).

Summary: Omega-6 fats are essential fats that are an important source of energy for the body. However, the Western diet contains too many.