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The Fatty Acids

This article discusses how much fat should be included in someone's diet:

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

Contents

Saturated Fats

Trans Fats

Monounsaturated Fats (MUFA)

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

Omega-6 Fatty Acids

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

Omega 3 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 descrease 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.


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. | link

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. | link

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. | link

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. | link

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. | link