The
Importance of Omega-3 Fatty Acids for Adults and Infants
Studies of Paleolithic nutrition and modern hunter-gatherer
populations suggest that humans evolved on a diet different
from today's typical North American diet. The diet of hunter-gatherers
was lower in total and saturated fat and contained small
but roughly equal amounts of omega-6 (n-6) and omega-3 (n-3)
long-chain fatty acids (LCFAs), giving an n-6/n-3 ratio of
about 1:1.1, 2 Paleolithic humans ate diets containing
appreciable amounts of omega-3 fatty acids provided by plants
and the fat of wild game.2 Technological developments
over the last 100 years have contributed to a shift in fat
consumption patterns. Specifically, the intakes of trans fatty acids, found mainly in products made with hydrogenated
vegetable oils, and omega-6 fatty acids, found in vegetable
oils and animal products derived from grain-fed livestock,
have increased over the past century.3 Compared
with the Paleolithic diet, the modern North American diet
is high in total and saturated fat, omega-6 fatty acids and trans fatty acids, and low in omega-3 fatty acids. This imbalance
has led some nutrition experts to recommend increasing omega-3
fatty acid intake. Omega-3 fatty acids are now known to be
essential for infant growth and development and to protect
against heart disease, thrombosis, hypertension and inflammatory
and autoimmune disorders.3
Is There an
Additional Requirement for Omega-3 Fatty Acids during Pregnancy
and Lactation?
Health Canada recommends
that pregnant women consume an additional 0.05 g of omega-3
fatty acids during the first trimester and an additional 0.16
g during the second and third trimesters. Lactating women should
increase their omega-3 fatty acid intake by an additional 0.25
g.5
Is There an Optimal Dietary
Ratio of Omega-6 to Omega-3 Fatty Acids?
The current dietary n-6/n-3
ratio ranges from about 10:1 to 25:1, indicating that typical
North American and Western diets are low in omega-3 fatty acids
compared with the Paleolithic diet on which humans evolved.3 Health
Canada recommends a ratio of 4:1 to 10:1, particularly for pregnant
and lactating women and infants.6 The FAO/WHO joint
committee recommends a ratio of between 5:1 and 10:1 and advises
individuals consuming diets with a higher ratio, to consume more
foods containing omega-3 fatty acids such as green leafy vegetables,
legumes and fish and other seafood.7 The U.S. Food
and Nutrition Board has not specified a dietary recommendation
for the n-6/n-3 fatty acid ratio.4
What Are
the Recommended Dietary Intakes of Essential Fatty Acids for
Adults?
Biochemical and clinical symptoms of essential fatty
acid (EFA) deficiency in adults can be prevented with a linoleic
acid intake of 1-2% of total energy. Omega-3 fatty acid intake
should be 10-25% that of linoleic acid or about 0.2-0.5%
of total energy.4 Health Canada has established
a Recommended Nutrient Intake (RNI) for the EFAs, specifying
a minimum daily intake of 3% of total energy for omega-6
fatty acids as linoleic acid and 0.5% of total energy for
omega-3 fatty acids as alpha-linolenic acid.5, 6 At
the present time, there is no Recommended Dietary Allowance
(RDA) for EFAs in the United States.4 A joint
Food and Agriculture Organization/World Health Organization
(FAO/WHO) committee recommends a desirable intake of linoleic
acid between 4 and 10% of energy.7 The British Nutrition Task Force recommends a minimum
of 0.5% of energy from alpha-linolenic acid.8
What Is the n-6/n-3 Fatty
Acid Ratio of Flaxseed?
Flaxseed contains more than
three times as much omega-3 as omega-6 fatty acids, giving an
n-6/n-3 ratio of 0.3:1. By comparison, the ratio for corn oil
is 58:1; for soybean oil, 7:1; and for canola oil, 2:1. The high
level of alpha-linolenic acid in flaxseed makes it a good source
of plant omega-3 fatty acids in the North American diet.
Is There an Optimal Intake of
Alpha-Linolenic Acid?
Based on measurements
of omega-3 fatty acids in plasma and erythrocyte lipids, the
optimal intake of alpha-linolenic acid has been estimated to
be 800-1100 mg/d for children and adults. The optimal intake
of the omega-3 LCFAs eicosapentaenoic acid (EPA) and docosahexaenoic
acid (DHA) is estimated to be 300-400 mg/d for children and
adults.3
Do Infants Require Omega-3
Fatty Acids for Growth and Development?
DHA is rapidly incorporated
into the lipids of the brain and retina during the last trimester
of pregnancy and the first year of life. Preterm infants fed
formula rich in DHA, for example, develop visual acuity more
rapidly than those fed standard infant formula low in omega-3
LCFAs.9 It is now widely recognized that dietary
omega-3 fatty acids, particularly DHA, are required for the
optimal development of the nervous system and maturation of
visual acuity in preterm and term infants.10, 11
Is Alpha-Linolenic Acid Alone
Sufficient to Meet the Needs of Infants for Omega-3 Fatty Acids?
If DHA is essential
for the growth and function of the retina and brain, then how
important is alpha-linolenic acid (ALA) in the diets of infants?
The data are not entirely clear on this point. Using visual
acuity as an indicator of infant development, two studies have
shown that feeding formula containing at least 2% ALA to low-birth-weight
infants12 and three-month-old infants13 resulted
in developments in visual acuity equivalent to that seen in
breast-fed infants. These studies suggest a specific role for
ALA in visual development. Other studies, however, suggest
that ALA alone is not sufficient to meet the EFA needs of infants
and that infants have a specific dietary need for DHA.14,
15 Very-low-birth-weight infants, for example, are unable
to synthesize sufficient omega-3 LCFAs from ALA to maintain
the usual level of incorporation of omega-3 LCFAs into plasma
and erythrocyte phospholipids.16 Thus, preterm infants
appear to require dietary DHA because they are unable to synthesize
sufficient DHA from soybean oil-based formula.9
Should Infant Formula Be Supplemented
with ALA, DHA and/or EPA?
The optimal fatty acid composition
of infant formula has not been determined. Prior to the 1990s,
most infant formulas contained low levels of ALA. Today, virtually
all infant formulas are supplemented with ALA; in some European
countries, infant formulas are
supplemented with ALA and DHA or ALA, DHA and
arachidonic acid.9 The main source of ALA for infant
formulas in North America is soybean oil. Experts agree that
infant formulas should be designed to approximate the fatty
acid composition of breast milk and include omega-3 fatty acids.3 Infants
may have a unique need for EFAs, particularly ALA, which is
the most prevalent omega-3 fatty acid in human milk.17 The
n-6/n-3 ratio of infant formula may be especially important,
as the relative amounts of these fatty acids influence the
amounts of DHA and arachidonic acid formed in tissues.18
References
1. Eaton SB and Konner M. N
Engl J Med. 1985;312:283-289.
2. Leaf A and Weber PC. Am
J Clin Nutr. 1987;45:1048-1053.
3. Simopoulos AP. Am J Clin Nutr. 1991;54:438-463.
4. Food and Nutrition Board, National
Research Council. In:Recommended Dietary Allowances, 10th
ed. Washington, DC: National Academy Press, 1989, pp.
44-51.
5. Murray TK and Beare-Rogers JL. J Can Diet Assoc. 1990;51:391-394.
6. Scientific Review Committee. Nutrition Recommendations. Ottawa, ON: Minister of National
Health and Welfare, Canada, 1990.
7. WHO and FAO Joint Consultation. Nutr Rev. 1995;53:202-205.
8. British Nutrition Foundation.
In: Unsaturated Fatty Acids: Nutritional
and Physiological Significance. New
York, NY: Chapman Hall, 1992.
9. Jørgensen MH, et al. Lipids. 1996;31:99-105.
10. Uauy R, et al. Lipids. 1996;31(Suppl):S167-S176.
11. Neuringer M, et al. Ann Rev
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12. nnis SM, et al. Am J Clin
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13. Innis SM, et al. Am
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14. Makrides M, et al. Lipids. 1996;31:115-119.
15. Luukkainen P, et al. J Pediatr Gasterenterol Nutr. 1996;23:229-234.
16. Boehm G, et al. Eur J Pediatr. 1996;155:410-416.
17. Budowski P, et al. World Rev
Nutr Diet. 1994;75:105-108.
18. Jensen CL, et al. Lipids. 1996;31:107-113.
Flax Council of Canada, 465-167 Lombard Ave., Winnipeg, MB, Canada R3B026,
email: flax@flaxcouncil.ca,
Website: http://www.flaxcouncil.ca/
