The Fatty Acids

Contents

• Saturated Fats
• Trans Fats
• Monounsaturated Fats
• Polyunsaturated Fats
  • Omega-3 Fatty Acids
    • 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

• Replacing saturated fats with polyunsaturated fats reduces the risk of heart disease (5).
• 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.
• The consensus among nutritional professionals is that large amounts of trans fats increase the risk of heart disease and many other diseases.
• 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).
• Also see 2010 Trans Fats Update.
• 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 (SDA)—short chain; 18:4(n-3)

• • There is evidence in humans that SDA is more readily converted to EPA than is ALA.
  • Echium plantagineum is a abundant source of SDA.
  • Ahiflower oil, a relatively new product, is extracted from Buglossoides arvensis seeds and is a rich source of SDA.

• Studies on SDA:
  • Lefort N, LeBlanc R, Surette ME. Dietary Buglossoides Arvensis Oil Increases Circulating n-3 Polyunsaturated Fatty Acids in a Dose-Dependent Manner and Enhances Lipopolysaccharide-Stimulated Whole Blood Interleukin-10-A Randomized Placebo-Controlled Trial. Nutrients. 2017 Mar 10;9(3).
  • Kuhnt K, Fuhrmann C, Köhler M, Kiehntopf M, Jahreis G. Dietary echium oil increases long-chain n-3 PUFAs, including docosapentaenoic acid, in blood fractions and alters biochemical markers for cardiovascular disease independently of age, sex, and metabolic syndrome. J Nutr. 2014 Apr;144(4):447-60.
  • 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 who get their EPA from seaweed. Vegan EPA supplements are 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

DPA has not been studied like EPA and DHA because it is not as prevalent in fish oil and isolated supplements have not been readily available – it is not known if it has any unique functions. A 2011 review (supported by Meat and Livestock Australia) 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 (7).”

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 is also made from DGLA. AA is converted into series 2 and 4 eicosanoids.

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. Too much LA will saturate this enzyme and prevent adequate ALA from being synthesized into EPA and DHA and thus increase inflammation from a lack of the series 3 eicosanoids.

However, a 2012 meta-analysis of studies on LA and inflammation found that in the recommended amounts, 3—10% of calories, LA did not increase markers of inflammation. Increased LA decreased EPA levels, but did not decrease DHA (1). A study from 1992 (6), vegans ate 9-10% of their calories as LA and, of course, had no natural dietary source of DHA. Whether large amounts of LA harm the DHA status of vegans has yet to be determined.

More information:

• Fat in Vegan Diets: How Low Should You Go?—by Virginia Messina, MPH, RD

References

1. Johnson GH, Fritsche K. Effect of Dietary Linoleic Acid on Markers of Inflammation in Healthy Persons: A Systematic Review of Randomized Controlled Trials. Journal of the Academy of Nutrition and Dietetics. 2012 Jul;112(7):1029-41.

2. Personal communication with Gary Fraser of the Adventist Health Study. October 22, 2001.

3. Fraser GE. Associations between diet and cancer, ischemic heart disease, and all-cause mortality in non-Hispanic white California Seventh-day Adventists. Am J Clin Nutr. 1999 Sep;70(3 Suppl):532S-538S.

4. Booker CS, Mann JI. Trans fatty acids and cardiovascular health: translation of the evidence base. Nutr Metab Cardiovasc Dis. 2008 Jul;18(6):448-56. Epub 2008 May 12.

5. Mozaffarian D, Micha R, Wallace S. Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS Med. 2010 Mar 23;7(3):e1000252. Review.

6. Sanders TA, Roshanai F. Platelet phospholipid fatty acid composition and function in vegans compared with age- and sex-matched omnivore controls. Eur J Clin Nutr. 1992 Nov;46(11):823-31.

7. Kaur G, Cameron-Smith D, Garg M, Sinclair AJ. Docosapentaenoic acid (22:5n-3): a review of its biological effects. Prog Lipid Res. 2011 Jan;50(1):28-34. Epub 2010 Jul 23. Review.