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The Fatty Acids

These two articles discuss how much fat should be included in someone's diet:

Fat in Vegan Diets: How Low Should You Go? by Virginia Messina, MPH, RD
The Challenge of Defining Optimal Fat Intake by Virginia Messina, MPH, RD

Contents

• Saturated Fats
• Trans Fats
• Monounsaturated Fats
• Polyunsaturated Fats
  • Omega-3s
    • Alpha-linolenic Acid
    • Stearidonic Acid
    • Eicosapentaenoic Acid
    • Docosapentaenoic Acid
    • Docosahexaenoic Acid
  • Omega-6 Fatty Acids
    • Linoleic Acid
    • Gamma Linolenic Acid
    • Dihomo Gamma Linolenic Acid
    • Arachidonic Acid
• PUFA Conversion Pathways
• References

Saturated Fats

• Many saturated fats raise the risk of heart disease.
• Found in high amounts in animal products; also in high amounts in coconut, palm, and palm kernel oils.

Trans Fats

• Found mostly in foods made with partially hydrogenated oils, including margarines, shortening, commercial frying fats, crackers, cookies, and other snacks. Check label. Butter and animal fat can also contain trans-fats from bacterial fermentation (1).
• The consensus among nutritional professionals is that large amounts of trans fats increase the risk of heart disease and many other diseases. For an article on what the research shows, see 2010 Trans Fats Update.
• A 2008 review (4) of trans fats and cardiovascular health found:
  • Five meta-analyses of controlled dietary interventions have examined the relationship between trans fatty acids intake and blood lipid levels and consistently report a worsening of blood lipid profiles with increasing trans fatty acid intakes, with a dose-response relationship evident.
  • Four cohort studies report on the association between trans fatty acid intake and incidence of cardiovascular disease. They consistently found that larger amounts of trans fats (about 4 to 6 grams per day) increased heart disease rates by about 25% in comparison with the lowest amounts (about 1 to 2 grams per day).
  • Vegetable based trans fats were found to be more harmful than animal-based (those found naturally in ruminent animal products).
• Earth Balance is a vegan margarine that contains omega-3s, no hydrogenated oils, and is available at many natural foods stores.

Monounsaturated Fats (MUFA)

• Also known as omega-9 fats, n-9, or oleic acid.
• Improve cholesterol levels when replacing saturated fats.
• Abundant in olive oil, canola oil, high oleic sunflower oil, hazelnut oil, high-oleic safflower oil, and almond oil.
• Olive oil is not as refined as other oils, making it a reliable source of vitamin E and possibly other healthy components. If you do not like the taste of olive oil in some dishes, try other oils made of high MUFA.
• Avocados and many nuts (almonds, cashews, filberts/hazelnuts, macadamias, peanuts, and pecans) are high in MUFA. Because nuts are high in nutrients and other protective compounds, you can benefit from eating them on a daily basis.
• In one study, eating nuts (including peanuts (2)) five or more times per week reduced heart disease by about 50% (3).

Polyunsaturated Fats (PUFA)

There are two main types of PUFAs: omega-3s (aka n-3) and omega-6s (aka n-6). Both n-3s and n-6s can be further divided into short chain and long chain.

The short chain n-3, alpha-linolenic acid (ALA), and the short chain n-6, linoleic acid (LA) are considered "essential," because the body cannot make them. Other PUFAs are not considered essential because most people's bodies can produce them from LA or ALA.

The following is a list of the notable PUFAs:

Omega-3s

• Alpha-linolenic Acid (ALA or LNA) - short chain; 18:3(n-3)

  • ALA is found mainly in the oil of flaxseeds, hemp seeds, walnuts, rapeseed (canola oil), camelina (aka Gold of Pleasure), chia seeds, and soybeans, and in animal flesh. It is also found in very small amounts in leafy green vegetables and other plant foods.

• Stearidonic Acid (STA) - short chain; 18:4(n-3)

  • Echiomega now (2010) sells a source of stearidonic acide from echium seed oil. Click here.

  • Croda Health Care has developed a product called Incromega V3 which contains stearidonic acid (STA). This product may be released in the USA soon (as of June 2007). There is evidence in humans that STA is more readily converted to EPA than is ALA. The STA in Incromega V3 is derived from the seed of the plant Echium Plantagineum. You can read more about it in this news story.

    Here are some studies on STA:

    • Surette ME, Edens M, Chilton FH, Tramposch KM. Dietary echium oil increases plasma and neutrophil long-chain (n-3) fatty acids and lowers serum triacylglycerols in hypertriglyceridemic humans. J Nutr. 2004 Jun;134(6):1406-11. Abstract.
    • Miles EA, Banerjee T, Calder PC. The influence of different combinations of gamma-linolenic, stearidonic and eicosapentaenoic acids on the fatty acid composition of blood lipids and mononuclear cells in human volunteers. Prostaglandins Leukot Essent Fatty Acids. 2004 Jun;70(6):529-38. Abstract.
    • James MJ, Ursin VM, Cleland LG. Metabolism of stearidonic acid in human subjects: comparison with the metabolism of other n-3 fatty acids. Am J Clin Nutr. 2003 May;77(5):1140-5. Abstract.

• Eicosapentaenoic Acid (EPA) - long chain; 20:5(n-3)

  • EPA is found mainly in fatty fish which get their EPA from eating seaweed. A vegan EPA supplement is now available. EPA is also present in Irish moss and wakame, but the ratio of iodine to EPA is much too high to make these foods a recommended source. Some EPA is converted into series 3 eicosanoids which can reduce inflammation, blood pressure, and cholesterol.

• Docosapentaenoic acid (DPA); 22:5n-3

  • A 2011 review says, "The literature on n-3 DPA is limited, however the available data suggests it has beneficial health effects. In vitro n-3 DPA is retro-converted back to EPA, however it does not appear to be readily metabolised to DHA."

• Docosahexaenoic Acid (DHA) - long chain; 22:6(n-3)

  • DHA is found in seaweeds and fatty fish. Vegan DHA supplements are available. DHA is a major component of the gray matter of the brain, retina, testis, sperm, and cell membranes. Low levels of DHA have been associated with depression. DHA can be converted into EPA.

Omega-6 Fatty Acids

• Linoleic Acid (LA) - short chain; 18:2(n-6)

  • LA is the most prevalent omega-6 fatty acid in plant foods and found in most vegetable oils, especially corn, sunflower, "vegetable," soy, safflower, and sesame oils.

• Gamma Linolenic Acid (GLA) - short chain; 18:3(n-6)

  • GLA is found in evening primrose oil, borage oil, black current oil, and breast milk.

• Dihomo Gamma Linolenic Acid (DGLA) - long chain; 20:3(n-6)

  • DGLA is made from GLA. Some DGLA is converted into series 1 eicosanoids which are considered good and so some people try to boost their DGLA through GLA supplements.

• Arachidonic Acid (AA) - long chain; 20:4(n-6)

  • AA is found in meat and peanut oil, and is also made from DGLA. AA is converted into series 2 and 4 eicosanoids which are considered bad. (Cats cannot convert LA to AA, which is why they must have AA supplemented in their diet if they are on a vegan diet.)

PUFA Conversion Pathways

Chart 1 below shows the order in which LA and ALA are converted into longer chain fatty acids and then into eicosanoids. Eicosanoids act like hormones with a direct effect on a wide range of physiological actions, including blood pressure, blood clotting, stomach secretions, cholesterol synthesis, respiratory muscle contraction, and effects on the immune and nervous systems. Many eicosanoids have opposing actions and, therefore, a balance of eicosanoids is needed.

Chart 1: PUFA Sources and Pathways

In the chart above, "D6D" represents the enzyme that changes ALA and LA into other fats. The reactions that convert LA and ALA compete for D6D. Because modern day diets are high in LA, LA wins this battle much of the time and people end up with too many of the series 2 and 4 eicosanoids. Series two and four are only considered "bad" because we tend to get too many; they are also necessary, but only in moderate amounts.

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References