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Omega-6 Fatty Acids and Health Fact Sheet
June 5, 2009
All about omega-6
Look around and you can’t help but notice that more and more people are talking about
omega-6 fatty acids. The conversation comes in the form of ratios and cutting back just as
often as it comes in advice for appropriate levels of consumption. Luckily, most people
are coming close to getting the required amount of omega-6s in their diets. But with hype
surrounding potential negative impacts of omega-6 consumption as well as increased
(and often confusing) discussions about omega-6/omega-3 ratios, it’s important to
understand the facts about omega-6 fats.
What are omega-6 fatty acids and where do they come from?
Researchers have known for more than 50 years that diets high in unsaturated fats help
reduce risk of heart disease by lowering blood cholesterol. In the 1950s and 1960s,
dietary advice to reduce heart disease risk included recommendations to increase intake
of unsaturated fats as well as reduce saturated fat and cholesterol in the diet. More recent
dietary guidance from the 2005 U.S. Dietary Guidelines for Americans recommends
keeping total fat intake between 20 to 35 percent of calories, with most fats coming from
sources of unsaturated fats, polyunsaturated and monounsaturated, such as fish, nuts and
vegetables oils.1
A Primer on Fats
Technically, fats should be referred to in the plural. Fats are combinations of many
different fatty acids that all play specific roles in the body, and they are named based on
their chemical structure, which can be either saturated or unsaturated. Saturated fats are a
string of carbon atoms, similar to a string of beads, and have no double bonds.
Unsaturated fats have double bonds within the carbon chain, which causes the structure to
bend, similar to how an arm bends at the elbow. Unsaturated fatty acids with one double
bond are called monounsaturated fatty acids (MUFAs), and those with more than one
double bond are called polyunsaturated fatty acids (PUFAs).
Polyunsaturated fats are further defined based on where the first double bond is found
within the carbon chain. These are known as omega-3 and omega-6 fatty acids. Two
types of polyunsaturated fatty acids are essential, meaning they must be consumed in the
diet because they cannot be produced by the body. These two fatty acids are linoleic acid,
which is an omega-6 fatty acid, and alpha-linolenic acid, which is an omega-3 fatty acid.
Omega-6 containing fats and oils are essential for life and recently their necessity for
health has been reconfirmed.2,3,4 Consumption of certain foods such as vegetable oils,
1 nuts and some fish are encouraged because of their healthful qualities, including fat
content, and their potential to reduce the risk of disease, including heart disease and
cancer.
Fatty acids exist in foods as mixtures, and certain foods are good sources of specific fatty
acids. For example, the principal polyunsaturated fats from vegetable sources include
linoleic acid (LA), an omega-6 fatty acid, found in soybeans, corn and sunflowers, and
alpha-linolenic acid (ALA), an omega-3 fatty acid, found in flaxseed and flaxseed, canola
and soybean oils. Long chain omega-3 fats such as eicosapentanoic acid (EPA) and
docosahexaenoic acid (DHA) are found in fatty fish such as salmon, sardines and
mackerel.
Sources of Omega-6 Fatty Acids*
Source
Safflower
oil
Sunflower
oil
Corn oil
Soybean
oil
Canola oil
Flaxseed
oil
Unsaturated Fats
Polyunsaturated Fats
Omega-6 fatty
Omega-3 fatty
acid (%)
acid (%)
74
0
Monounsaturated
Fats %
14
66
0
53
50
20
13
Saturated
Fats %
6
% of Oil
Used in
U.S. Food
Supply+
<1
20
10
~2
1
7
27
23
13
16
~6
~ 56
9
53
59
20
7
9
~ 11
n/a
*Extracted from USDA National Nutrient Databank, Agricultural Research Service, accessed at: http://www.ars.usda.gov/main/site_main.htm?modecode=12-35-45-00.
+Extracted from USDA Economic Research Service. 2008 Oil Crops Yearbook: Table 31 Edible fats and oils: Supply and Disappearance, U.S., 1993/942008/09 available at: http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1290.
Omega-6 consumption recommendations
In 2002, the Institute of Medicine (IOM) reviewed the evidence for dietary fat
requirements and recommended that between five and 10 percent of total calories should
come from the omega-6 fat linoleic acid to have beneficial effects on coronary heart
disease (CHD); slightly less is required after age 50.5 This is an acknowledgement of the
critical value of this fat for health. The following chart, “Omega-6 and Omega-3 Fatty
Acids: Recommended and Usual Intakes,” provides recommended and usual intake data
for two specific types of omega-6 and omega-3 fats.
In the body, omega-6 fats, specifically linoleic acid, are elongated to form arachidonic
acid, which is incorporated into cells and cell membranes providing structural support. It
also can be found in vital organs such as the brain, eyes and kidneys and is an important
part of cell signaling.
2 Essential Omega-6 and Omega-3 Fatty Acids: Recommended and Usual Intakes
Adequate Intake
Usual Intake from
Usual Intake
Adequate Intake
from Food, Men (AI), Women 19Food, Women
(AI), Men 19-50y 1
50y 1
19y+ 2
19y+ 2
Omega-3
1.7 g/day
1.1 g/day
1.3 g/day
(alpha-linolenic 1.6 g/day
acid)
Omega-6
17 g/day
16.8 g/day
12 g/day
12.7 g/day
(linoleic acid)
1 Institute of Medicine, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids,
2002.
2 What We Eat in America, NHANES 2001-2002.
The omega-6/omega-3 ratio
Despite these recommendations from the IOM, ongoing study of optimal amounts of
polyunsaturated fats in the diet has led to the premise that a specific balance of omega-6
and omega-3 fats is necessary for maximizing the benefits of these fats.6 Some scientists
believe that diets high in omega-6 fats relative to omega-3 fats may be associated with
increased prevalence of chronic diseases, including heart disease and certain cancers.6,7,8
This theory has led to the proposed use of a target intake ratio of omega-6/omega-3 fats
for assessing health risk and making dietary recommendations for a person’s diet as well
as individual foods.
The ratio of omega-6/omega-3 fatty acids in today’s diet is estimated to be about than 9.8:1, with
some estimates as high as 20-25:1.9 A few studies suggest that a much lower ratio of omega-6 to
omega-3 fats, ranging between 2:1 and 5:1, is desirable in reducing the risk of disease, including
heart disease, cancer and autoimmune disorders.7,8 Yet, recently a group of nutrition scientists
was convened by the American Heart Association to assess the validity of a target ratio. These
scientists found that the use of a ratio as dietary advice for individuals is not only difficult to
measure and implement, but there are flaws and limitations in applying a target ratio for
assessing risk of disease.10
Other researchers indicate that the ratio between the two fatty acids is unimportant, but
the absolute amounts of each type of fatty acid are critical. They cite the well-established
role of linoleic acid to lower blood cholesterol levels; further, they recognize the clinical
and epidemiological evidence for the value of omega-3 fats, especially fish oils, to reduce
coronary heart disease risk. This research suggests that it is not necessary to change the
omega-6/omega-3 fats ratio by lowering intake of omega-6 fatty acids; it is beneficial to
raise omega-3 intakes, especially from fish, to the levels recommended by dietary
guidance.11
Most evidence to date highlights the beneficial role that both omega-6 and omega-3 fats
play in reducing risk of disease, not their relationship to each other.4 While groups such
3 as the American Dietetic Association, the American Heart Association (AHA) and the
U.S. Dietary Guidelines Advisory Committee encourage the consumption of fish during
meals, particularly fish rich in long chain omega-3 fatty acids, this encouragement does
not diminish the value of omega-6 fatty acids for health.12,13,1 At this time, research does
not demonstrate a need to reduce daily intake of omega-6 fats, to the contrary if
individuals begin to reduce their intake of omega-6 fats rates of coronary heart disease
(CHD) may actually increase, which would have a negative impact on public health.4
Omega 6 and heart health
Dietary factors can play a major role in the risk of heart disease. Numerous studies have shown
how consumption of certain foods may impact total blood cholesterol, including low-density
lipoprotein (LDL) or “bad cholesterol,” high-density lipoprotein (HDL) or “good cholesterol,” as
well as triglycerides. Research from experimental animals, laboratory investigations,
epidemiology, and genetic forms of hypercholesterolemia indicate that elevated LDL cholesterol
is a major cause of CHD. In addition, recent clinical trials robustly show that LDL-lowering
therapy reduces risk for CHD. Therefore, the primary strategy for reducing risk of heart disease
focuses on reducing LDL cholesterol.14
Epidemiological studies of large populations over a number of years can detect changes
in diet over time and can compare individual intakes for a number of nutrients. The
Nurses’ Health Study, which followed 99,000 women and the Health Professional
Follow-Up Study, which involved 51,000 men, found an inverse relationship between
intake of linoleic acid and CHD.15,16,17 The findings showed that people who consumed
more omega-6 fats in the form of linoleic acid and more omega-3 fats experienced a
reduced risk of developing CHD. These studies point to linoleic acid’s role in reducing
LDL cholesterol as well as reducing the ratio of total cholesterol to HDL cholesterol,
which is another risk factor for heart disease. Linoleic acid also may act by reducing
blood triglyceride levels following a meal or as a means of curbing adverse heart
arrhythmias.15
Clinical trials help to clarify the mechanisms related to omega-6 fats and cholesterol
reduction, and new studies continue to add insights.18,19,3 In the body, the 18-carbon fatty
acids linoleic acid and alpha linolenic acid are elongated to 20 carbon chains, which form
hormone-like substances called eicosanoids. Eicosanoids are necessary for normal
immune function, inflammation and blood coagulation. The long chain omega-3 fats
(EPA and DHA) found in fish may reduce cardiovascular disease by suppressing
inflammatory factors. Omega-6 fats likely reduce cardiovascular disease via changes in
many other systems, such as those affecting oxygen availability, blood flow, insulin
resistance and blood pressure.20,21 An analysis of 60 clinical studies found that
polyunsaturated fatty acids (primarily linoleic acid) lowered LDL cholesterol, raised
HDL cholesterol and reduced total triglyceride levels compared with carbohydrates.22
More research is needed to understand the cardiovascular effects of various fats.
Although much is written about the benefits of omega-3 fats, large population
4 epidemiological studies and clinical studies affirm that higher consumption of omega-6
fats is significantly related to lower risk of CHD. This inverse correlation occurs in men,
women, and younger as well as older individuals.23,24,2 Additionally, a recent AHA
Science Advisory states that the consumption of at least five percent to 10 percent of
energy from omega-6 fats reduces the risk of CHD relative to intakes below five percent
of energy.4
Cancer and omega-6 fatty acids
The World Cancer Research Fund and the American Institute for Cancer Research
released an evidenced-based report on food, nutrition, physical activity and cancer
prevention. The report found that there is limited evidence to suggest that total fat intake
is a cause of breast, lung or colorectal cancers.25 Further, studies examining the
relationship between specific fatty acids and cancer do not provide a clear picture. A
meta-analysis, which evaluated linoleic acid and risk of breast, prostate and colorectal
cancer found little data to suggest an increased risk of cancer and linoleic acid intake.26
The large Japanese Collaborative Cohort Study, which looked at the development of
colorectal cancer in normal individuals over a seven year period, showed no appreciable
effect of omega-6 fats on increased risk of colorectal cancer.27 Another study indicated
that omega-6 fats were inversely associated with colorectal cancer risk, but the effect was
not statistically significant.28
However, omega-6 fats also may play a role in breast and pancreatic cancer incidence.
Dietary consumption of omega-6 fats was correlated with lower incidence of breast
cancer.29 Preliminary research with specific breast tissue and cancer risk is less
conclusive, with cell studies showing both protective and potentially harmful effects.30,31
Similarly, preliminary research evaluating pancreatic cancer cells have also shown both
beneficial and protective effects of omega-6 on pancreatic cancer risk.32,33
The relationship between omega-6 fats and cancer continues to emerge, and is
compounded by the need to better understand how omega-6 fats may play a role in
various mechanisms of action in the body. While all cancers are unique and carry their
own set of risk factors, current consensus recommendations from the National Cancer
Institute recommend that to reduce risk of cancer individuals should quit smoking,
manage their weight by increasing physical activity and managing their calories,
consuming more fruits and vegetables, and practice avoidance of alcohol.34
Additional impacts of omega-6
Given the recent increase in allergy and asthma cases and the connection between the
long chain polyunsaturated fatty acids eicosanoids, which play a role in inflammation and
immune function, some scientists have speculated that omega-6, omega-3, or the ratio of
dietary omega-6/omega-3 fats might be associated with allergies. However, a detailed
respiratory survey that included dietary intake and blood tests, revealed no association
between fatty acid intake and hay fever or between the ratio of omega-6/omega-3 fats in
blood serum and hay fever or allergic sensitivity.35
5 More recent research is evaluating polyunsaturated fats and the effects they may have on
the body as we age. Decline in the speed of nerve conduction is a common occurrence of
aging. An Italian study found that total dietary polyunsaturated content predicted
significantly less decline in nerve conduction velocity (NCV) as well as a second
measure of nerve function in individuals less than 65 years of age.36 Higher baseline
omega-6 fatty acid intake predicted less NCV decline in those between 65 and 84 years
of age. This study appears to confirm and expand the Rotterdam study report, which
found a relationship between total polyunsaturated fatty acids and reduced risk of
Parkinson’s disease.37 Although the authors do not recommend supplementation with
omega-6 fats to improve peripheral neuropathy, they recommend further studies to
explore this concept.
In summary
The evidence is clear that omega-6 fats are essential for optimal functioning of the body
and health maintenance. Studies consistently demonstrate their role in lowering total
cholesterol and reducing risk for coronary heart disease. Fat is an important part of the
diet, along with carbohydrates and protein, and as long as individuals are not exceeding
their daily calorie requirements, there is no need to limit the amount of omega-6 in the
diet. Additional research evaluating the function of omega-6 fats and their dietary sources
will help to promote a better diet for all.
References
1. US Department of Health and Human Services, US Department of Agriculture, Dietary
Guidelines for Americans, 2005, US Department of Health and Human Services website.
http://www.health.gov/dietaryguidelines/dga2005/document/default.htm, Accessed
September 15, 2008.
2. Willett WC, The role of dietary n-6 fatty acids in the prevention of cardiovascular disease, J
Cardiovasc Med, 2007; 8 (suppl 1):S42-S45.
3. Lands B, A critique of paradoxes in current advice on dietary lipids, Prog Lipid Res, 2008,
47:77-106.
4. American Heart Association Nutrition Subcommittee; Council on Cardiovascular Nursing;
and Council on Epidemiology and Prevention. American Heart Association Science Advisory
Omega-6 fatty acids and risk of cardiovascular disease. Circulation, 2009; 119:0-0.
5. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol,
Protein, and Amino Acids. Institute of Medicine. 2002. Washington, DC
6. Wijendran V and Hayes KC, Dietary n-6 and n-3 fatty acid balance and cardiovascular
health, Annu Rev Nutr, 2004; 24:597-615.
7. Simopoulos AP. The importance of the ratio of omega-6/omega-3 essential fatty acids.
Biomed Pharmacother. 2002;56:365-79.
6 8. Simopoulos AP, The importance of the omega-6/omega-3 fatty acid ratio in cardiovascular
disease and other chronic diseases, Exp Biol Med 2008; 233:674-688.
9. Kris-Etherton PM, Taylor D, Yu-Poth S, et al. Polyunsaturated fatty acids in the food chain in the
United States. Am J Clin Nutr. 2000;71(suppl):179S–88S.
10. Harris WS. The omega-6/omega-3 ratio and cardiovascular disease risk: Uses and abuses.
Curr Athero Rep. 2006;8:453-9.
11. Sanders TA, Oakley FR, Miller GJ, et al. Influence of n-6 versus n-3 polyunsaturated fatty
acids in diets low in saturated fatty acids on plasma lipoproteins and hemostatic factors.
Arteriosscler Thromb Vasc Biol. 1997;17:3449-60.
12. Kris-Etherton PM, Innis S, Position of the American Dietetic Association and Dietitians of
Canada: Dietary fatty acids, J Am Diet Assoc, 2007; 107:1599-1611.
13. American Heart Association Nutrition Committee, Diet and lifestyle recommendations
revision 2006: a scientific statement from the American Heart Association Nutrition
Committee, Circulation, 2006; 114:82-96.
14. National Institutes of Health. National Heart, Lung, and Blood Institute. Third Report of the National
Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of
High Blood Cholesterol in Adults (Adult Treatment Panel III). NIH Publication No. 01-3670. May
2001. http://www.nhlbi.nih.gov/guidelines/cholesterol/atp3xsum.pdf Accessed January 16, 2009.
15. Hu FB, Stampfer MJ, Manson JE et al. dietary fat intake and the risk of coronary heart
disease in women. N Engl J Med. 1997; 337:1491-1499.
16. Ascherio a. Epidemiologic studies on dietary fats and coronary heart disease. Am J Med.
2002; 113:9S-12S.
17. Ascherio A, Rimm EB, Giovannucci EL, et al. Dietary fat and risk of coronary heart disease
in men: cohort follow up study in the United States. Br Med J. 1996; 313:84-90.
18. Binkoski AE, Kris-Etherton PM, Wilson TA et al, Balance of unsaturated fatty acids is
important to a cholesterol-lowering diet: Comparison of mid-oleic sunflower oil and olive oil
on cardiovascular disease risk factors. J Am Diet Assoc; 2005; 105:1080-1086.
19. Ferrucci L, Cherubini A, Bandinelli S, et al, Relationship of plasma polyunsaturated fatty
acids to circulating inflammatory markers, J Clin endoc Metab, 2006; 91:439-446.
20. Kris-Etherton PM, Harris WS, Appel LJ et al. Fish consumption, fish oil, omega-3 fatty acids,
and cardiovascular disease, Circulation 2002; 106:2747-2757.
21. Sacks FM and Campos H. Editorial: Polyunsaturated fatty acids, inflammation, and
cardiovascular disease: time to widen our view of the mechanisms, J Clin Endocrinol Metab.
2006; 91:398-400.
22. Mensink RP, Zock PL, Kester ADM et al. Effects of dietary fatty acids and carbohydrates on the ratio
of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60
controlled trials, Am J Clin Nutr. 2003; 77:1146-1155.
7 23. Mozaffarian D, Ascherio A, Hu FB, et al, Interplay between different polyunsaturated fatty
acids and risk of coronary heart disease in men, Circulation 2005; 111:157-164.
24. Oh K, Hu FB, Manson JE et al, Dietary fat intake and risk of coronary heart disease in
women: 20 years of follow-up of the nurses’ health study, Am J Epidemiol 2005; 161:672679.
25. World Cancer Research Fund/American Institute for Cancer Research. Food, Nutrition,
Physical Activity, and the Prevention of Cancer: A Global Perspective. Washington, DC:
AICR, 2007.
26. Zock P, Katan M. Linoleic acid intake and cancer risk. Am J Clin Nutr, 1998; 68:142-153.
27. Kojima M, Wakai K, Tokudome S et al. Serum levels of polyunsaturated fatty acids and risk
of colorectal cancer: a prospective study, Am J Epidemiol 2005; 161(5):462-471.
28. Hall MN, Campos H, Haojie L, et al. Blood levels of long-chain polyunsaturated fatty acids,
aspirin, and the risk of colorectal cancer. Cancer Eiipdemiol. Biomarkers Prev 2007;
16(2):34-321.
29. Rissanen H, Knekt P; JArvinen R et al. Serum fatty acids and breast cancer incidence. Nutr
Cancer. 2003; 45:168-175.
30. Bagga D, Anders KH, Wang HJ et al, Long-chain n-3-to-n-6 polyunsaturated fatty acid ratios
in breast adipose tissue from women with and without breast cancer. Nutr Cancer. 2002;
42:180-185.
31. Jiang WG, Hiscox S, Bryce RP et al, The effects of n-6 polyunsaturated fatty acids on the
expression of nm-23 in human cancer cells, J Cancer, 1998; 77:731-738.
32. Funahashi H, Satake M, Hasan S, et al. Opposing effects of n-6 and n-3 polyunsaturated fatty
acids on pancreatic cancer growth, Pancreas, 2008; 36:353-362.
33. Bravi F,Bosetti C, Dal Maso L, et al, Macronutrients, fatty acids, cholesterol, and risk of
benign prostatic hyperplasia, Urology, 2006; 67:1205-1211.
34. US Department of Health and Human Services, National Institutes for Health, National
Cancer Institute. Cancer Prevention Overview. National Cancer Institute Web site.
http://www.cancer.gov/cancertopics/pdq/prevention/overview/healthprofessional Accessed
June 1, 2009.
35. Kompauer H, Demmelmair B, Koletzko G et al, n6/n3 Hypothesis and Allergies: Biologically
Plausible but not Confirmed, Eur J Med Res, 2004; 9:378-82
36. Lauretani F, Bandinelli S, Benedetta B et al. Omega-6 and omega-3 fatty acids predict
accelerated decline of peripheral nerve function in older persons, Eur. J. Neurol. 2007;
14:801-808.
37. de Lau LML, Bornebroek M, Witteman JCM et al, Dietary fatty acids and the risk of
Parkinson disease, The Rotterdam Study, Neurology 2005; 64:2040–2045.
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