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Nutrition and Metabolism

Omega-3

What is omega-3?

Omega-3 is a group of essential fatty acids that are required but not synthesized by human body. There are three major omega-3 fatty acids in human diets: ALA, EPA, and DHA. ALA is abundant in certain plant oils. EPA and DHA can be synthesized from ALA by human body but are also abundant in fish oil (Table 1).

Omega-3 refers to the polyunsaturated fatty acids that contain a double bond at the third carbon atom from the methyl end. Polyunsaturated fatty acids are the ones that have two or more double bonds between carbon atoms of the carbon chain.

Omega-3 fatty acids are opposite of omega-6 fatty acids, which contain a double bond at the sixth carbon atom from the methyl end. While omega-3 fatty acids are anti-cardiovascular diseases, anti-inflammation, and are generally under supplied to human body, omega-6 fatty acids are pro-cardiovascular diseases, pro-inflammation, and over-abundant in modern western diets.  More detailed information about the opposite effects of omega-3 and omega-6 fatty is available here.

Table 1. The most common omega-3 and omega-6 fatty acids and their dietary sources.

Types Abbreviation Common Name Structure Dietary Sources
Omega-3 ALA α-Linolenic acid C18 : 3 Flaxseed oil, olive oil, canola oil
EPA Eicosapentaenoic acid C20 : 5 Fish oil, marine algae
DHA Docosahexaenoic acid C22 : 6 Fish oil, marine algae
Omega-6 LA Linoleic acid C18 : 2 Corn oil, soybean oil, sunflower seeds oil and peanut oil
AA Arachidonic acid C20 : 4 Peanut oil. Small amount in meat, dairy products and eggs

How is omega-3 used in human body?

Omega-3 fatty acids are the precursors of many signaling molecules, regulators of gene expression and structural components of the cell membrane. In addition, the two long chain omega-3 fatty acids EPA and DHA are required in high levels in the brain and retina to support optimal neuronal functions.

How much omega-3 do I need in my diet?

The Institute of Medicine of the National Academies recommends omega-3 to make up between 0.6% and 1.2% of the total daily energy for Americans.  This amount is equivalent to about 1.3 to 2.6 g of ALA (or 1 to 2 table spoons of canola oil, or about 3 oz of salmon fillet) for a person consuming 2000 calories per day.

Why is omega-3 more important for people carrying certain gene variants?

Sufficient dietary omega-3 is beneficial to general population but it is especially beneficial to people with certain genetic variants.  For example, a variant of the eNOS gene that with a 34% frequency in Caucasians is associated with increased risk for hypertension and high blood triglycerides when omega -3 intakes are insufficient. However, when omega-3 intakes increase to 1.24 g per day for 12 weeks, the risks are reduced significantly, to levels even lower than in the general population. A variant of the ALOX5 with a 20% frequency in the population is associated with increased risk for atherosclerosis.  The risk is significantly reduced by increased dietary omega-3. Therefore, for these genetic variant carriers, sufficient omega-3 intake is more important than for the general population.

Which foods contain high level of omega-3?

ALA is most abundant in plant-based food sources (Table 2) while deep sea animals are rich in EPA and DHA. (Table 3).

Table 2. ALA-rich food sources.

Food Serving ALA (g)
Flaxseed oil 1 tablespoon 7.3
Walnuts, English 1 oz 2.6
Flaxseeds, ground 1 tablespoon 1.6
Walnut oil 1 tablespoon 1.4
Canola oil 1 tablespoon 1.3
Soybean oil 1 tablespoon 0.9
Mustard oil 1 tablespoon 0.8
Tofu, firm ½ cup 0.7
Walnuts, black 1 oz 0.6

Table 3. EPA/DHA-rich sea foods.

Food Serving EPA (g) DHA (g)
Herring, Pacific 3 oz 1.06 0.75
Salmon, Chinook 3 oz 0.86 0.62
Sardines, Pacific 3 oz 0.45 0.74
Salmon, Atlantic 3 oz 0.28 0.95
Oysters, Pacific 3 oz 0.75 0.43
Salmon, sockeye 3 oz 0.45 0.6
Trout, rainbow 3 oz 0.4 0.44
Tuna, canned, white 3 oz 0.2 0.54
Crab, Dungeness 3 oz 0.24 0.1
Tuna, canned, light 3 oz 0.04 0.19

Plant-derived (ALA)
Flaxseeds, oil
Per 100 g (g) 53.7
Per Serving (g) 7.3
Serving Size 1 tablespoon
 
Flaxseeds, ground
Per 100 g (g) 11.8
Per Serving (g) 1.6
Serving Size 1 tablespoon
 
Walnut oil
Per 100 g (g) 10.3
Per Serving (g) 1.4
Serving Size 1 tablespoon
 
Canola oil
Per 100 g (g) 9.6
Per Serving (g) 1.3
Serving Size 1 tablespoon
 
Walnuts, English
Per 100 g (g) 9.2
Per Serving (g) 2.6
Serving Size 1 oz (28 g)
 
Soybean oil
Per 100 g (g) 6.6
Per Serving (g) 0.9
Serving Size 1 tablespoon
 
Mustard oil
Per 100 g (g) 5.9
Per Serving (g) 0.8
Serving Size 1 tablespoon
 
Walnuts, black
Per 100 g (g) 2.1
Per Serving (g) 0.6
Serving Size 1 oz (28 g)
 
Tofu, firm
Per 100 g (g) 0.6
Per Serving (g) 0.7
Serving Size 1/2 cup (126 g)
Sea Food (EPA + DHA)
Fish, salmon
Per 100 g (g) 1.7
Per Serving (g) 1.5
Serving Size 3 oz (85 g)
 
Fish, sardine
Per 100 g (g) 1.4
Per Serving (g) 1.2
Serving Size 3 oz (85 g)
 
Sea food, Oysters
Per 100 g (g) 1.4
Per Serving (g) 1.2
Serving Size 3 oz (85 g)
 
Fish, rainbow trout
Per 100 g (g) 1.0
Per Serving (g) 0.8
Serving Size 3 oz (85 g)
 
Fish, herring
Per 100 g (g) 2.1
Per Serving (g) 1.8
Serving Size 3 oz (85 g)
 
Sea food, Crab, Dungeness
Per 100 g (g) 0.4
Per Serving (g) 0.3
Serving Size 3 oz (85 g)

How can vegans get EPA and DHA in their diets?

The human body can convert ALA to EPA and DHA so vegans do not need to worry about dietary EPA and DHA as long as they are getting sufficient ALA from plant oils and/or nuts.

Is it better to get omega-3 fatty acids from food or from supplements?

It is always better to get your nutrients from your diet than from supplements. But if you are in a situation where you cannot get sufficient omega-3 in diet, you should consider taking a supplement.  People with certain conditions such as those who have had heart attacks are normally advised by health providers to take omega-3 supplements.

How do I increase my omega-3 intake?

First, use the GB Food and Nutrition Calculator to get an assessment of your current omega-3 intake level. Then follow the guidelines below to ensure you’re getting a healthy dose of omega-3.

  1. Increase the amount of omega-3 rich food in your diet (See tables 2&3).
  2. Try to use canola oil or olive oil in home cooking to increase ALA in home-made foods. Please be aware that the level of ALA in olive oil (0.76%) is about half of the level in canola oil.  So using olive oil alone without any other omega-3 rich sources would not provide sufficient dietary omega-3.
  3. Limit corn oil, peanut oil and cotton seeds oil in home cooking.  These oils do contain high level of polyunsaturated fatty acids.  But they have too much omega-6 and little to no omega-3.
  4. Cut down peanut and sunflower seeds based snacks.  These are fat-rich, energy-dense foods and lack omega-3.
  5. Take omega-3 supplements if you cannot get enough in your diets.

 

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