An Introduction to Dietary Fatty Acids
By Elena Tateo, MS RD and CJ Segal-Isaacson, EdD RD

 

    The fatty acid composition of the diet affects various aspects of human health (1).  Dietary lipids (fats) are essential components of living cells and are incorporated into the lipid structures of cell membranes.  They are also important sources for energy and are precursors for numerous biologically active compounds (2).

      Current research involving common dietary fatty acids in human nutrition has provided us with a better understanding of how these specific fatty acids relate to cardiovascular and other diseases, and has helped us explore the role they play in human physiology.  The purpose of this review and the development of the Fatty Acid Chart displayed below is to provide the AECOM medical student with relevant information regarding individual fatty acids.  The data has been compiled to highlight cholesterolemic effects of individual fatty acids and their implications in human health. Dietary notes and web links have been provided, and are intended for informational purposes only.

      Fat provides energy, and if a particular fatty acid is added to the diet, an equivalent amount of some other energy yielding food component must be removed or the subject will gain weight.  Thus, the effect of a certain amount of energy provided by a specific fatty acid can only be expressed relative to a similar quantity of energy provided by another dietary component that serves as a reference (3).  The fatty acids described in the Fatty Acid Chart were reviewed primarily to evaluate their effects on serum lipids. Because oleic acid is considered in research to be neutral in its effects on serum lipids, we reviewed studies comparing diets designed with fats high in their respective dietary fatty acid compared with diets high in oleic acid. Some studies used olive oil in place of oleic acid or as a placebo for comparison.  Since olive oil is naturally high in oleic acid, and supplementation did not alter plasma or platelet phospholipid oleic acid and other fatty acid concentrations, its use as a substitute is justified(4). Please note that marine oil containing Eicosapentaenoic acid and Decosahexaenoic acid was the most common source of supplementation in studies comparing Omega-3 fatty acids with oleic acid.

In the Fatty Acid Chart below, the name, type and code of an individual fatty acid, along with a summary of their effects on serum lipids, health implications, and dietary sources is listed.

 

Fatty Acid Chart 

  Key to chart

­= increase    ¯= decrease    NS= Not significant (P>0.05)   NE= No effect

Fatty Acid Name

Fatty Acid Type & Code

Intake Patterns

in grams per day/as percent of total energy (16)

    Effects on Serum Lipids

Health Implications 

Common Food Sources and Dietary Notes 

Men Women

TG

LDL

HDL

TC

Linoleic Acid

(Omega 6 or LA)

PUFA

18:2, n-6

14.7/ 6.0 

10.4g/ 6.3 

¯NS

 

¯NS

 

¯NS

 

¯NS

 

 

(14)

Essential FA;  specifically required in skin to maintain integrity of epidermal water barrier. Precursor to arachidonic acid, required for eicosanoid-mediated inflammatory and immune cell functions, and tissue proliferation. Competes with n-3 for eicosanoid production. Optimal ratio of n-6/n-3 intake may be 4:1 or lower.  High dietary intake of n-6 may increase susceptibility to LDL oxidation (5) 

Oils (g/tablespoon) 

  • Safflower (­ linoleic type): 10.1g

  • Sunflower: 9.3 g

  • Corn: 7.9  g

  • Soybean: 6.9  g

  • Peanut: 4.3 g

 n-6 PUFA’s are very common in the American diet; used in many commercially processed goods. Found naturally in nuts, seeds and vegetable oils. 

alpha- Linolenic acid

(Omega 3 or ALA)

PUFA

18:3, n-3

1.6/ 0.6 

1.1g/ 0.7 

¯

 

 

­

 

 

­NS

 

 

NE

(15)

ALA is an Essential FA; precursor to eicosapentaenoic acid (EPA) and decosahexaenoic (DHA). Main biologic activity appears to reside in retina, testes, and CNS; critical to development of CNS in infants (5). Influence on cellular events through synthesis of eicosenoid derivatives, gene expression, acting as second messenger signaling molecules, and modulating cellular responses to extracellular signals (6). n-3 FA’s appear to have antithrombotic, anti-inflammatory and hypolipemic properties; they may be useful in prevention and treatment of atherothrombotic diseases. (7)  

Eicosapentaenoic acid (EPA) and decosahexaenoic acid (DHA) have a wide range of biological effects.  Those relevant to heart disease include influences on lipoprotein metabolism, platelet and endothelial function, vascular reactivity, neutrophil and monocyte cytokine production, coagulation, fibrinolysis, and blood pressure. DHA may be retroconverted to EPA(7); however EPA has not been found to elongate to DHA.  

Current evidence suggests that n-3 fatty acids can be safely used in people with diabetes to modulate cardiovascular risk factors, such as elevated triglycerides, without impairing glycemic control (17).

*The increase in LDL by DHA supplementation reflects a relative increase in LDL particle size, which may be considered antiatherogenic. 

ALA

Oils (g/ tablespoon)  

  • Flaxseed: 8g       

  • Canola: 1.3g  

  • Soybean: 1.0g 

  • Mustard:  0.8g

Nuts, seeds (g/1 oz) & Beans (g/100g or ~ 4.5 oz) 

  • Flaxseed: 6.5g

  • Walnuts: English 2.6g, Black .9g    

  • Soybeans: .35g  

  • French Beans: .3g

    EPA/DHA

Fish (g/100g or ~ 3.5 oz) and oil (g/tablespoon): 

  • Herring: .9/1.1 g

  • Mackerel: .5/.7g  

  • Sardines .5/.5g

  • Salmon: .4/1.4g 

  • Tuna: .4/1.4g

  • Swordfish .14/.7g

  • Cod liver oil: .9/1.5g

ALA can also be found in some green plants, algae, phytoplankton, and mustard oil.  EPA and DHA are found primarily in marine oil and fish. 

Average therapeutic dose: 3-4g marine oil.  FDA has ruled that intakes up to 3 grams per day of marine n-3 fatty acids are now “generally recognized as safe” for inclusion in the American Diet (11).  See “Health Implications” for more details.

EPA 

(Omega 3)

PUFA

20:5, n-3

0.1/0.04 

    based on total EPA and DHA combined 

¯

 

 

­NS

 

 

¯

HDL3

 

 

NE

 

 

 

 

 

(4)

DHA

(Omega 3)

PUFA

22:6, n-3

¯

 

­*

 

­

HDL2

 

Oleic acid

MUFA

Cis 18:1, n-9

31.0/ 12.7

20.8/ 12.5

Studies which substitute oleic acid for SFA resulted in a significant decrease in TC and LDL. HDL and TG reduction was not consistently shown.  In a meta-analysis comparing diets high in MUFA or PUFA, it was reported that both diets elicited similar total and lipoprotein–cholesterol lowering effects (12). For practical purposes, it is convenient to use oleic acid as a baseline with which to judge the responses of other fatty acids.

While there is much evidence that oleic acid improves lipid profiles by reducing cholesterol compared with SFA's, there is new evidence suggesting that oleic acid may be proatherogenic by altering properties of LDL.  Oleic acid  may  be protective against breast cancer relative to SFA's(5). MUFA bonds are not as easily oxidized as PUFA in phospholipid  membrane of LDL(5) inferring a protective role against oxidative degradation. 

The body synthesizes large quantities of oleic acid suggesting a variety of biological advantages. Studies comparing relative carcinogenicity of FA’s or ability to suppress the immune system suggest that oleic acid is one of the most benign of FA’s(8).

Oils (g/ tablespoon) & Nuts  (g/1 oz) 

  • Olive oil: 9.8g

  • Soybean Oil: 3.1g

  • Canola oil: 7.85g   

  • Safflower Oil (­oleic type): 10.2g  

  • Almonds: 9.0g   

  • Cashews: 7.6g    

  • Pecans: 11.5g  

  • Avocado (100g); California:10.7g, Florida:4.1g

  • Peanut Butter (2 Tbs): 7.6g  

Oleic acid is the predominant MUFA in the American diet (91-95% of MUFA intake) (12).

Lauric acid

SFA, 12:0

0.9   /0.4

0.7/      0.4 

­NS

 

 

­

 

 

­NS

 

 

­

(14)

Palmitic acid is the most predominant SFA in the American diet (3,8) Although studies have reported relative lipid changes when substituting one SFA for another, it is well-established that SFA’s are hypercholesterolemic and increase CHD risk relative to MUFA and PUFA. Current evidence also suggests that SFA intake may correlate with increased insulin resistance (17).

Stearic acid is reported to have neutral effects on lipoproteins(8), similar to oleic acid when compared with other SFAs. However, distinction between stearic acid and other SFAs are not supported when giving dietary advice at this time(9), since stearic acid naturally coexists with other SFAs in food. 

Fatty cuts of meat, poultry skin, whole or 2% milk products (including cheese, ice cream, butter), egg yolk, shortening, and products using these items in their ingredients. 

Of the foods relatively high in SFA, whole milk dairy products, especially cheeses, are relatively higher in lauric & myristic acids while certain cuts of lean beef and pork are relatively higher in stearic acid;  Coconut and palm kernel oils are significantly higher in lauric & myristic acid and palm oil is relatively high in palmitic acid. Cocoa butter oil and chocolate are  relatively high in stearic acid, but are also rich in palmitic acid.  

Low or non fat animal products and derivatives are good food choices when trying to reduce SFA in the traditional American diet. 

Myristic acid

SFA, 14:0

2.7/  1.1 

1.9/      1.1 

­NS

 

 

­

 

 

­

 

 

­

(14)

Palmitic acid

SFA, 16:0

17.0/ 7.0

11.6/    7.0 

­NS

 

 

­

 

 

­NS

 

 

­

(14)

Stearic acid

SFA, 18:0

8.1/   3.3

5.4/      3.3 

­NS

 

­NS 

 

­NS

 

­NS

(14)

Elaidic acid

TFA

Trans 18:1, n-9

~3-6% of energy  intake (13) 

­

 

 

 

 

­

 

 

¯

 

 

­

(14)

Hydrogenation of vegetable oils has led to an increase of TFA in the food supply. The degree of hydrogenation by the food manufacturer dictates how much TFA is in the product. Diets high in trans fatty acids interfere with desaturation and elongation of EFA. The physical properties and lipid related health implications of TFA are similar and sometimes worse than  those of SFA (10).

Many types of margarine, shortening,  salad dressing, processed peanut butter, commercially prepared baked goods (cakes, cookies, breads, crackers, French fries, doughnuts, chips/corn snacks) and products with the words “partially hydrogenated… oil” listed in the ingredients.  Manufacturers are now making some of these items available as “trans fat free.” 

*See Health Implications.

Conclusion

General dietary guidelines for fat intake supported by the American Heart Association are as follows:

As the depth of our knowledge increases, it is likely that we will further tailor dietary fat prescriptions to more specifically fit the needs of a particular individual. 

For more information about current dietary fat recommendations and other helpful information, visit the American Heart Association website at www.Americanheart.org.

 

References  

Food composition data obtained from USDA Nutrient Database for Standard Reference, Release 13 - (Formerly known as Handbook 8)

1.      Schmidt, DE, Allred, JB, Kien, CL.  Fractional oxidation of chylomicron-derived oleate is greater than that of palmitate in healthy adults fed frequent small meals. Journal of Lipid Research. 1999, 40:2322-2332.

2.      Alexander, JW.  Immunonutrition: The role of ω-3 fatty acids. Nutrition.  1998, 14:627-633.

3.      Katan, MB, Zock, PL, Mensink, RP.   Effects of fats and fatty acids on blood lipids in humans: an overview. Am J Clin Nutr. 1994, 60(suppl):1017S-22S.

4.      Mori, TA, Burke, V, Puddey, IB, Watts, FR, O’Neal, DN, Best, JD, Beilin, JL.   Purified eicosapentaenoic and decosahexaenoic acids have differential effects on serum lipids and lipoproteins, LDL particle size, glucose, and insulin in mildly hyperlipidemic men. Am J Clin Nutr. 2000, 71:1085-94.

5.      Shils, ME, Olson, JA, Shike, M, Ross, AC. 1999. Modern Nutrition in Health and Disease. (Ninth Ed.) Baltimore. Williams & Wilkins.

6.      Segal-Isaacson, CJ, Wylie-Rosett, J. The cardiovascular effects of fish oils and omega-3 fatty acids. Heart Disease. 1999, 1:149-154.

7.      Hansen, JB, Grimsgaard, S, Nilsen, H, Nordoy, A, Bonaa, KH. Effects of highly purified eicosapentaenoic acid and docosahexaenoic acid on fatty acid absorption, incorporation into serum phospholipids and postprandial triglyceridemia. Lipids. 1998, 33:2:131-138.

8.      Grundy, SM.  Influence of stearic acid on cholesterol metabolism relative to other long-chain fatty acids. Am J Clin Nutr.  1994, 60(suppl):986S-90S.

9.      Hu, FB, Stampfer, MJ, Manson, JE, Ascherio, A, Colditz, GA, Speizer, FE, Hennekens, CH, Willet, WC. Dietary saturated fats and their food sources in relation to the risk of coronary heart disease in women. Am J Clin Nutr. 1999,  70:1001-8.

10.  Simopoulos, AP. Omega-6/Omega-3 fatty acid ratio and trans fatty acids in non-insulin-dependent diabetes mellitus.  Annals New York Academy of Sciences. 1997. 1997, 827:327-338.

11.  Kris-Etherton, PM, Harris, WH. Fish Consumption, fish oil, omega-3 fatty acids and cardiovascular disease.  Unpublished data.

12.  Jonnalagadda, SS, Mustad, VA, YU, S, Etherton, TD, Kris-Etherton, PM. Effects of individual fatty acids on chronic diseases. Nutrition Today.  1996, 31:90-106. 

13.   Judd, JT, Clevidence, BA, Muesing, RA, Wittes, J, Sunkin, ME, Podczasy, JJ.  Am J Clin Nutr.  1994, 59:861-8.   

14.   Kris-Etherton, PM,Yu, S.  Individual fatty acid effects on plasma lipids and lipoproteins: human studies. Am J Clin Nutr.  1997. 65(suppl):1628S-44S. 

15.  Harris, W.  n-3 fatty acids and serum lipoproteins: human studies.  Am J Clin Nutr.  1997, 65(suppl):1645S-54S.  

16.  Jonnalagadda, SS, Egan, K, Heimbach, JT, Harris, SS, Kris-Etherton, PM.      Nutrition Research. 1995, 15:12:1767-1781.

17.  Segal-Isaacson, CJ, Carello, E, Wylie-Rosett, J. . Current Diabetes Reports. October 2001,1(2):161-169

Other articles of interest

 Clarke SD. Polyunsaturated fatty acid regulation of gene transcription: a mechanism to improve energy balance and insulin resistance. Br J Nutr. 2000, 83 Suppl 1: S59-66. 

Rudel LL, Haines J, Sawyer JK, Shah R, Wilson MS, Carr TP. Hepatic origin of cholesteryl oleate in coronary artery atherosclerosis in African green monkeys. Enrichment by dietary monounsaturated fat. J Clin Invest. 1997, 100: 74-83.

Higashi K, Shige H, Ito T, Nakajima K, Ishikawa T, Nakamura H, Ohsuzu F. Effect of a low-fat diet enriched with oleic acid on postprandial lipemia in patients with type 2 diabetes mellitus. Lipids. 2001, 36: 1-6.

Bergman RN, Van Citters GW, Mittelman SD, Dea MK, Hamilton-Wessler M, Kim SP, Ellmerer M. Central role of the adipocyte in the metabolic syndrome. J Investig Med. 2001, 49: 119-126.

Last updated 2002