• MEMBRAN SEL

Polyunsaturated
fatty acids (PUFA)
INTRODUCTION
Fatty acids are components of fat. They are mostly bound or
attached to other molecules, such as in triglycerides or phospho-
lipids. When they are not attached to other molecules, they are
known as "free" fatty acids. Fatty acids (Figure 1) are linear
hydrocarbon chains with a methyl (CH3-, also called the ω-end)
and a carboxyl (-COOH) end. Fatty acids vary in their number of
carbon atoms and double bonds and are classified as follows1:
• Saturated fatty acids (SFA, no double bonds)
• Monounsaturated fatty acids (MUFA, one double bond)
• Polyunsaturated fatty acids (PUFA, two or more double bonds)
• Omega-6 PUFA
• Omega-3 PUFA
Omega-6 PUFA (also known as ω-6 PUFA, n-6 PUFA) have the
first double bond at carbon number 6 counting from the methyl
end. The major omega-6 PUFA in the diet are:
• linoleic acid (LA)
• γ-linolenic acid (GLA)
• arachidonic acid (AA)
Omega-3 PUFA (also known as ω-3 PUFA, n-3 PUFA) have the
first double bond at carbon number 3 counting from the methyl
end. The major omega-3 PUFA in the diet are:
• alpha-linolenic acid (ALA)
• eicosapentaenoic acid (EPA)
• docosahexaenoic acid (DHA)
Both saturated and monounsaturated fatty acids can be
synthesized by the human body. Linoleic acid (LA) and
a-linolenic acid (ALA) however, are essential nutrients and must
be obtained from a dietary source to avoid deficiency2. LA can
be metabolized to arachidonic acid and docosapentaenoic acid
(DPA) in the human body. ALA can be transformed to
eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)
(Figure 2). Recent studies demonstrate that the conversion rate
to EPA and DHA is very low, so much so that it is being suggested
EPA and DHA become regarded as essential themselves3.
1 COOH
H3C 16
Palmitic Acid
1 18
H3C COOH
9 Oleic Acid
6
1 COOH
H3C 18
Linoleic Acid
1 18
H3C COOH
3 a-linolenic Acid
Figure 1: Chemical structures of saturated, monounsaturated
and polyunsaturated fatty acids (the carbon atoms are
numbered beginning at the methyl end)
Information Fact Sheets
 ω-3 fatty acid ω-6 fatty acid ω-9 fatty acid
Polyunsaturated fatty acids as precursors
a-Linolenic
acid (18:3 n-3)
Linoleic acid
(18:2 n-6)
Oleic acid
(18:1 n-9)
for eicosanoids
ALA LA DGLA, AA and EPA give rise to eicosanoids, a group of
biologically active substances that control physiologically
γ-Linoleic acid
(18:3 n-6) important processes such as blood pressure, renal function,
GLA blood coagulation, inflammatory and immunological reactions4.
Homologous omega-6 PUFA and omega-3 PUFA compete
Di-homo-γ-Linoleic
acid (20:3 n-6) against each other and for the same metabolic enzymes (Figure
DGLA
3). For instance, EPA intake increases the tissue concentration
of EPA and lowers that of AA. Concomitantly, there is a shift
Eicosapentaenoic Arachidonic acid
acid (20:5 n-3) (20:4 n-6) of eicosanoids in favour of the eicosanoids derived from EPA
EPA AA
by having lesser inflammatory activity than those derived from
AA. Studies have shown that high omega-6 intakes tend to
Docosahexaenoic Docosapentaenoic
acid (22:6 n-3) acid (22:5 n-6) Eicosatrienoic shift the physiological state to one that is proinflammatory
DHA DPA acid (20:3 n-9) and prothrombotic, characterized by high blood viscosity,
vasoconstriction and short bleeding times. Omega-3 PUFA,
Figure 2: Enzymatic conversion of different omega fatty acids
however, have anti-inflammatory, antithrombotic, antiarrhythmic,
vasodilatory and triglyceride lowering properties4,5. There is
ample evidence that high AA/EPA tissue ratios contribute to
the development of chronic diseases in later life such as
IMPORTANCE FOR HEALTH
coronary heart disease and stroke, cancer or diabetes1.
Polyunsaturated fatty acids as structural
Phospholipid pool in cell membrane
components of bio-membranes
Omega-6 and omega-3 PUFA are important structural
components of the phospholipid cell membranes of the tissues,
which have multiple physiological functions4,5. The composition
of the phospholipids influences cell membrane characteristics
such as fluidity and permeability to other molecules. They are
essential for various membrane functions such as activity of Phospholipase A2
membrane-bound enzymes and receptors, and signal
transduction. Here are some examples:
Skin: Arachidonic acid (AA) Eicosapentaenoic acid (EPA)
Omega-6 PUFA are integral components of skin lipids6.
LA is incorporated into skin ceramides, which is essential
for maintaining the water permeability barrier of the skin. Cyclooxygenase
Excessive trans-epidermal water loss should be avoided6. Lipoxygenase
A prolonged lack of dietary omega-6 PUFA has been shown to
increase trans-epidermal water loss, causing rough and scaly
Pro-inflammatory Eicosanoids Anti-inflammatory Eicosanoids
skin, and may contribute to the development of dermatitis1.
Prostaglandin Series 2 Prostaglandin Series 3
Brain: TXA2, PGE2, PGI2 TXA3, PGE3, PGI3
Leukotriene Series 4 Leukotriene Series 5
The developing brain accumulates large amounts of PUFA LTB4, LTC4, LTE4 LTB5, LTC5, LTE5
both pre- and postnatally. AA and DHA are the major PUFA
in the brain, nervous tissue and retina6. DHA seems to be Figure 3: Eicosanoids from AA and EPA compete against
essential for the visual process in the retina and for proper each other
brain functioning7.
1 Institute of Medicine, F.N.B., Dietary 2 Jones, P.J.H., Kobow, S., Lipids, Sterols, 3 Burdge G.C., Calder P.C., Conversion 5 Simopoulos A.P., Omega-3 fatty acids
References
Fats: Total Fat and Fatty Acids, in and Their Metabolites, in Modern Nutrition of a-linolenic acid to long-chain in inflammation and autoimmune disease,
Dietary Reference Intakes for Energy, in Health and Disease, Shils, M.E., et al., polyunsaturated fatty acids in human Journal of the American College of
Carbohydrate, Fiber, Fat, Fatty Acids, Editors. Williams & Wilkins: Baltimore. adults, Reprod. Nutr. Dev. 2005: 45: Nutrition, 2002: 21(6): 495-505
Cholesterol, Protein and Amino Acids. 1999: 67- 94 581-597
National Academy Press: Washington DC. 4 Simopoulos, A.P., Essential fatty acids in
2005: 422-541 health and chronic disease. Am J Clin Nutr,
1999: 70(3 Suppl): 560S-569S
 FOOD SOURCES FOOD FORTIFICATION
Dietary fatty acids derive from both animals and plants Foods (e.g. bread, dairy products, dressings, meats, eggs)
(Table 1). In general, animal fats are high in saturated fatty enriched with omega-3 PUFA (ALA, EPA and DHA) have become
acids. Vegetable oils tend to be higher in unsaturated fatty available and are an alternative to increase the intake of these
acids and are therefore liquid at room temperature1. PUFA6. For fortification purposes, two product forms are
Rich sources of omega-6 PUFA include nuts, seeds and available: oils and powders (produced by microencapsulation
most oils used in the kitchen, with the exception of olive oil. technology). The powdered products can be used in baked
Certain specialty oils, such as blackcurrant, evening primrose goods, bars, cereals, dietetic products, etc. Oil emulsions are
and borage seed oils, are high in GLA. AA is present in small suitable for use in liquid food matrices8. No estimates are available
amounts in meat, poultry, and eggs. It is practicably absent on the contribution of fortified foods to the total intake of omega-6
in plant-derived fats and oils1. or omega-3 PUFA, especially DHA and EPA, in Europeans6.
Omega-3 PUFA are found in some vegetable oils, fish and
seafood8. Soybean, rapeseed and walnut oils are high in ALA.
DHA and EPA are found exclusively in fish and seafood and RECOMMENDED INTAKES
to a lesser extent in egg yolk and meat6. Dietary omega-6 and
omega-3 PUFA are almost completely absorbed in the small Recommendations for total PUFA intakes vary between 2.5
intestine of healthy individuals7. and 12% of the total daily energy intake (En%, Table 2).
Recommendations for intakes of omega-6 PUFA and omega-3
Table 1: Food sources of polyunsaturated fatty acids9 PUFA vary between 2 - 10 and 0.5 - 2 En%, respectively. The
SCF defined Population Reference Intakes (PRI) of 2 En% for
PUFA (g/100g)
Total fat omega-6 PUFA and 0,5 En% for omega-3 PUF10. This corresponds
Food source Total
ω-3 PUFA ω-6 PUFA (g/100g) to a daily intake of approximately 6 g/day and 8 g/day for a typical
PUFA
adult female and male, respectively. The corresponding
Coconut oil 1.80 0 1.80 100 amounts for omega-6 PUFA are 5 g/day and 6.4 g/day and for
Corn oil 56.2 1.05 55.2 100 omega-3 PUFA 1 g/day and 1.6 g/day, respectively. The Nordic,
D-A-CH and Dutch recommendations also apply to pregnant and
Olive oil 7.64 0.56 7.07 100
lactating women. The French ANC recommends somewhat
Rapeseed oil 33.2 11.1 22.1 100
higher intakes during pregnancy and lactation6.
Salmon, raw 3.36 3.01 0.36 10.0
Soybean oil, Table 2: Recommended daily intakes of PUFA for adults as a
60.4 6.88 53.5 100
refined proportion of the total daily energy intake (En%) according to
Sunflower oil 63.0 0 63.0 100 different institutions6
Walnuts 43.9 7.46 36.4 64.3 PUFA (En%)
Country/
organisation Total ω-6 PUFA ω-3 PUFA
D-A-CH*, 2000 3 2.5 0.5
France (ANC), 2001 5 4 1
PUFA SUPPLEMENTS
Netherlands (DRI),
3 – 12 2 1
Available omega-3 PUFA food supplements contain EPA 2001
and DHA derived from marine oils in varying proportions, and Nordic countries
5 – 10 ≥4 ≥1
contain 180 mg EPA and 120 mg DHA per capsule. Typical cod (NNR), 2004
liver oil supplements contain 173 mg EPA and 120 mg DHA. SCF, 1993 2.5 2 0.5
For vegetarians there is an alternative in the form of DHA oils
UK (DoH), 1991 6.5 - -
derived from algae (100 mg DHA per capsule)8.
USA (FNB), 2002 5.6 – 11.2 5 – 10 0.6 – 1.2
WHO/FAO, 2003 6 – 10 5–8 1–2
* Recommendations for Germany, Austria and Switzerland
6 European Food Safety Authority (EFSA), 7 Innis, S.M., Essential Dietary Lipids, in 8 Kris-Etherton, P.M., Taylor, D.S., Yu- 9 Danish Institute for Food and Veterinary
Opinion of the Scientific Panel on Dietetic Present Knowledge in Nutrition, Ziegler, Poth, S., Huth, P., Moriarty, K., Fishell, V., Research, The Danish Food Composition
Products, Nutrition and Allergies on a E.E. and Filer, L.J., Editors. ILSI Press: Hargrove, R.L., Zhao, G.,Etherton, T.D., Databank. 2006, Ministry of family and
request from the Commission related Washington D.C. 1996 Polyunsaturated fatty acids in the food consumer affairs: http://www.foodcomp.
to nutrition claims concerning omega- chain in the United States. Am J Clin Nutr, dk/fcdb_default.asp
3 fatty acids, monounsaturated fat, 2000: 71(1 Suppl): 179S-188S
polyunsaturated fat and unsaturated fat.
The EFSA Journal, 2005: 253: 1 - 29
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The differences in recommendations reflect different nutritional In general, dietary intakes of omega-6 PUFA are well above the
goals. The SCF10 and D-A-CH11 recommendations for omega-3 recommendations defined in Table 2. Dietary intakes of omega-
PUFA are based on the amounts necessary to correct clinically 3 PUFA vary with the amounts and types of vegetable oils and
overt omega-3 PUFA deficiency and to which a safety fish in the diet6. Whereas the observed intakes of total omega-3
allowance was added. The recommendations for total omega-3 PUFA and ALA as percent of the energy intake are close to the
PUFA formulated by WHO13 were based on considerations of SCF recommendations, the intakes of long-chain omega-3 PUFA
cardiovascular health and neurodevelopment. such as DHA or EPA are mostly lower than recommended by
There are only a few dietary recommendations for individual national authorities. In general, it was observed that the intake
omega-3 PUFA or omega-6 PUFA. The Food and Nutrition of the long-chain PUFA EPA or DHA increases with age in
Board recommends 1.6 g/d (men) / 1.1 g/d (women) of ALA1. parallel with an increase in fish consumption6.
In France recommendations for long-chain omega-3 PUFA
have been established (500 mg/d for men and 400 mg/d for
women)6. The WHO recommendation of 1-2 servings of fish
SAFETY
per week corresponds to 200-500 mg of EPA and DHA12.
As mentioned above, omega-6 and omega-3 PUFA compete Data on the safety of PUFA intakes above 10 En% are limited.
for the same enzymes. Therefore, in addition to the reference No UL has been set for either omega-6 PUFA or omega-3 PUFA
values for groups or individual fatty acids, ratios of omega-6 because no intake level could be established at which adverse
and omega-3 PUFA have also been recommended. As can be effects occur1. The most common adverse affects include
calculated from Table 2 the omega-6/omega-3 PUFA ratio varies gastrointestinal discomfort and nausea. The gastrointestinal
between 2:1 and 10:1, depending on whether adequate or events were therefore most likely in response to the ingestion
upper level values are selected. There is no consensus about of such a large volume of an oily substance as opposed to the
the optimal omega6/omega-3 PUFA ratio in the diet. actual omega-3 PUFA. Very high doses (> 20 g/d) of omega-3
PUFA might be associated with increased bleeding times14.
However moderate consumption (ranging up to 7.5 g/day)
does not appear to cause this15. That would mean that PUFA
CURRENT INTAKES amounts commonly used in supplements are safe.
Recent surveys in several European countries reported average
intakes of total PUFA ranging from 3 to 7 En% (Table 3).
In many countries the average PUFA intake was below 6 En%,
the lower limit of the WHO recommendations12.
Table 3: Dietary intakes of PUFA by adults in Europe6
PUFA (En%)
Total ω-6 PUFA ω-3 PUFA
Country M W M W M W
Finland 5.2 4.9 4.1 3.8 1.1 1.0
Germany 4.6 4.8 - - - -
Greece 6.0 7.0 - - - -
Italy 5.0 - - - -
Sweden 4.6 4.7 3.7 4.0 0.7 0.7
The Netherlands 7.0 6.8 - - - -
United Kingdom 6.4 6.3 5.4 5.3 1.0 1.0
M = Men, W = Women
10 SCF (Scientific Committee on 11 DGE, Referenzwerte für die 13 Elmadfa, I. and Weichselbaum, E., 14 Mata Lopez, P. and Ortega, R.M.,
References
Food), Commission of the European Nährstoffzufuhr. 1 ed. Frankfurt: Umschau Energy and Nutrient Intake in the European Omega-3 fatty acids in the prevention and
Communities. Reports of the Scientific Braus Verlagsgesellschaft. 2000 Union. European Nutrition and Health control of cardiovascular disease. Eur J Clin
Committee for Food: Nutrient and energy 12 WHO (World Health Organisation), Diet, Report 2004. Forum Nutr. Basel, Karger, Nutr, 2003: 57 Suppl 1: S22-S25
intakes for the European Community. nutrition and the prevention of chronic 2005: 58: 19-46 15 Hathcock J., Richardson D., Shao A.,
(Thirty-first series). 1992, Office for Official diseases. Report of the WHO/FAO Joint Jennings S., The risk assessment and
Publications of the European Communities: Expert Consultation. WHO Technical safety of bioactive substances in food
Luxembourg. p. http://europa.eu.int/comm/ Report Series 916. 2003: Geneva. p. http:// supplements. IADSA, 2006: 52-57
food/fs/sc/scf/out89.pdf whqlibdoc.who.int/trs/WHO_TRS_916.pdf