S1B4 - Omega 3s

Question 1

What is the difference between an omega 3 and an omega 6 fatty acid?

Answer 1

The terminal methyl carbon is referred to as the omega (ω) carbon.

• If the last C-C double bond is 3 from the ω C, the fatty acid is an ω-3 (or n-3) PUFA.
• If the last C-C double bond is 6 from the ω C, the fatty acid is an ω-6 (or n-6) PUFA.

Question 2

What are the essential fatty acids for humans? Why these ones?

Answer 2

Essential fatty acids for humans are linoleic and α-linolenic acids.

• Humans can form C-C double bonds in fatty acids no farther away from the carboxylic carbon than 9 (Δ9 desaturation).
• Linoleic (an n-6 PUFA) gives rise to the “n-6 series” of PUFAs such as arachidonic.
• α-Linolenic (an n-3 PUFA) gives rise to the “n-3 series” of PUFAs such as EPA and DHA.
• Oleic acid (an n-9 MUFA) gives rise to the “n-9 series” of FAs, such as nervonic (24:1, n-9).

Question 3

Where on a fatty acid can humans make double bonds?

Answer 3

Humans can form Δ9, Δ6, Δ5, and Δ4 double bonds in fatty acids.

Question 4

What is the preferred substrate for Δ9 desaturation?

Answer 4

The preferred substrate for Δ9 desaturation is stearic acid to yield oleic acid. In fact, this enzyme system is often called stearoyl desaturase.

Question 5

Elongation and desaturation of which fatty acid is used to synthesize arachidonic acid?

Answer 5

Elongation and desaturation of linoleic acid is used to synthesize arachidonic acid.

Question 6

What can elongation and desturation of α-linolenic acid produce. Can humans utilize this process?

Answer 6

Elongation and desaturation of α-linolenic acid can produce eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, the utilization of α-linolenic acid to synthesize EPA and DHA is limited in humans.

Question 7

What fatty acid is utilized to synthesize arachidonic acid?

Answer 7

Linoleic acid is utilized to synthesize arachidonic acid.

• Arachidonate is the precursor of prostaglandins, and thromboxanes of the “2” series, and leukotrienes and lipoxins of the “4” series.

Question 8

What fatty acid is utilized to synthesize EPA, and DHA?

Answer 8

α-linolenic acid, as noted above, may be utilized to synthesize EPA, and DHA.

• Note that EPA may be utilized by cyclooxygenase and lipoxygenase to form prostaglandins and thromboxanes of the “3” series, and leukotrienes of the “5” series.

Question 9

What may DHA and EPA be used to synthesize? How are these made? What do they do? why are they important?

Answer 9

DHA and EPA may be used to synthesize lipid mediators called resolvins and protectins.

• Oxidation of EPA and DHA by some of the same enzymes which use arachidonic acid as a substrate, produce the resolvins and protectins.
• These compounds appear to act in a manner to resolve acute inflammation.
• These appear to be important in the brain, where DHA is abundant.
• DHA is known to be important in the normal visual and neurological development.

Question 10

What are the dietary sources of essential fatty acids?

Answer 10

• Linoleic acid is found in numerous vegetable oils, including corn, safflower, soy, etc.
• α-Linolenic acid is found in land based plant oils such as walnut, soy, canola, etc.
• EPA and DHA are found in fish.
  
  • Especially high in cold water, fatty, large fish.
  • EPA and DHA are synthesized by cold water plants, and are concentrated in fish “up the food chain”.
  • A fairly comprehensive table is appended for those who are interested.

Question 11

What are some documented health benefits of n-3 PUFAs?

Answer 11

1. Decreased cardiovascular disease events with n-3 PUFA consumption
2. Decreased dyslipidemia
3. Decreased rheumatologic conditions
4. Decreased hypertension
5. Improved vision development and decreased vision disorders
6. Improved neurological function

Question 12

What are potential adverse effects associated with n-3 PUFA intake?

Answer 12

• Allergy to fish
• Mercury, PCB poisoning
• Bleeding

Question 13

Summarize the recommendations for Omega-3 fatty acid intake.

Answer 13

Patients without documented CHD

• Eat a variety of (preferably oily) fish at least twice a week. Include oils and foods rich in α-linolenic acid (flaxseed, canola, and soybean oils; flaxseed and walnuts)

Patients with documented CHD

• Consume ~1 g of EPA+DHA per day, preferably from oily fish. EPA+DHA supplements could be considered in consultation with the physician.

Patients needing triglyceride lowering

• Two to four grams of EPA+DHA per day provided as capsules under a physician’s care