Omega 3 is definitely a hot topic these days and we're now hearing that plant sources of omega 3 (ie flax seeds) are not as good a source as marine sources. This will be the first of many blogs on omega 3s cause there's so much to talk about!
Let's start with a bit of an explanation of omega 3s. Alpha-linolenic acid (ALA) is a plant source omega-3 essential fatty acid (EFA). It is “essential” because our bodies can’t make it. Two other omega-3 fats are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
ALA is found mainly in flax seeds and walnuts, and in flax, canola and soybean oils. EPA and DHA are found mainly in fatty fish such as herring, salmon, mackerel and bluefin tuna, and the fish oil supplements made from them. Marine algae, the base of the oceanic food chain, are rich sources of DHA but contain little EPA.
EPA is not technically “essential” because our bodies make it from ALA, although conversion is not efficient and rates vary, based on many factors. DHA conversion from ALA is so poor that some authorities think it should be classified as “conditionally essential.”
Conversion of ALA to DHA and EPA
The overall conversion efficiency from ALA to EPA plus DHA combined is estimated to be only 12%. However, the conversion of ALA to DHA has been found to be highly variable between people and was found to be as low as less than 0.1% (and a conversion to EPA plus DHA combined of less than 0.4%) in one study. Yet another study, this one from the U.K., has compared the apparent conversion efficiency of ALA to DHA in young adult men and women. Interestingly, no detectable formation of DHA was found in the men whereas an approximate conversion efficiency from ALA to DHA of 9% was found in women.
In summary, the conversion efficiency from ALA to DHA is very limited in healthy individuals.
Do we need DHA? Yes! 30 years ago, work done at the Department of Nutrition at the University of Guelph showed that the feeding of omega-3 enriched diets to female rats prior to mating and throughout pregnancy and lactation along with the feeding of similar diets to their babies resulted in the pups showing superior learning capacity compared to the group that had diets with negligible levels of omega-3. These authors correlated the superior learning ability in the omega-3 fed animals to higher levels of DHA in the brain tissue. Subsequent studies from numerous labs have supported these early findings and have led to the conclusion that DHA is a physiologically-essential fatty acid required at high levels in brain tissue for optimal neurological performance and functioning.
DHA is known to significantly alter many basic properties of cell membranes. These various properties and mechanisms of action of DHA in the nervous system are thought to underlie its role in brain functioning such as learning ability, memory, etc.
The high levels of DHA in the brain and nervous system are actively deposited particularly during the last trimester of pregnancy and during the first two months of infancy and very early years of a child's life.
A study of 815 elderly people living in Chicago found that those with the highest DHA intake had the most protection against Alzheimer’s disease. Several neurological/behavioral disorders have been suggested to be associated with depressed levels of DHA or DHA plus EPA combined. These not only include Alzheimer's, but depression (including post-partum depression), behavioral disorders such as Attention Deficit Hyperactivity Disorder (ADHD) and hyperactivity, as well as developmental coordination disorder.
EPA and DHA keep cell membranes flexible/elastic and block the actions of some compounds that cause inflammation and clotting. Chronic conditions like heart disease, diabetes, cancer, arthritis, certain skin disorders, gastrointestinal disorders (ie. Crohn's, inflammatory bowel disorders) are marked by inflammation. DHA and EPA have been shown to help reduce the risk of these chronic diseases by blocking inflammation and have also been found to improve many of these conditions.
Lots of studies have also shown an inverse relationship between the consumption of fish containing EPA + DHA and the risk of cardiovascular disease (CVD) and cardiac death. Higher intakes of DHA and EPA can lead to reductions in fasting triglyceride levels, lowering of the triglyceride:HDL-cholesterol ratio, thinning of the blood, reduction in blood clots, lowered resting heart rate, reduced carbohydrate-induced blood fat surges after a meal and reduced atherosclerotic plaques. Population studies have also revealed apparent benefits of consuming fish containing DHA plus EPA in a wide variety of conditions including chronic eye conditions (cataracts, dry eye), epilepsy, allergic sensitivity in very young children, pneumonia, lung/breathing capacity and chronic pulmonary disorders, plus other conditions recently reported including bone and joint health and fibromyalagia.
Where do we get DHA and how much do we need?
DHA plus EPA are completely absent from plant food sources rich in ALA (such as flax, canola oil, and walnuts). Since the metabolic conversion of ALA to DHA/EPA (combined) by metabolism is very limited in humans, the most direct way of providing DHA plus EPA for the body is via their direct consumption.The American Heart Association and the Canadian Heart & Stroke Foundation has recommended two fatty fish servings per week for people who are healthy individuals without cardiovascular disease. The DHA plus EPA (combined) equivalency of such fish consumption is approximately 250-300 mg/day.
The American Heart Association in its official Dietary Guidelines (2000) recommended that the daily intake of DHA plus EPA in individuals with coronary heart disease should target 900 mg/day since this amount has shown to be beneficial in affecting coronary heart disease mortality rates in patients with coronary disease. Consumption of one fatty acid meal per day (or alternatively, a fish oil supplement) could result in an omega-3 fatty acid intake (i.e. EPA and DHA) of ~900mg per day
Increasing intakes of DHA/EPA (combined) up to approximately 650-700 mg/day (4-5 fatty fish dishes/week) are associated with overall reductions in all-cause as well as coronary disease-related mortality.
A study showed that those consuming 5 or more servings fatty fish per week had a 31% overall reduction relative to those eating fish less than once per month. It is possible that other components in fish other than DHA/EPA may offer benefits independent of or synergistic to DHA + EPA.
What if you don't want to eat fish?
For many reasons- over-fishing, the buildup of toxic minerals and other toxic substances in fish flesh, environmental problems, and cruelty to fish and sea mammals- fish are becoming less and less of a desirable source of DHA and EPA for many people. Vegetarians who consume an average of 4-5 regular eggs per week would have a daily intake of DHA of approximately 33 mg with 3 mgs present as EPA. The ovo (egg-eating) vegetarian could increase their daily intake of DHA considerably by consuming omega-3 eggs such as are becoming commonplace in the North American marketplace.
The absence or low-levels of DHA in the diet of vegetarians is reflected in their physiological levels of DHA such as that present in expressed breast milk. The levels of DHA in breast milk (total fat) from vegan women have been found to be approximately one-third the levels found in the breast milk from omnivorous women.
For vegan vegetarians who consume no fish or animal food sources whatsoever, increasing their intake of dietary ALA (omega-3) as well as reducing their intake of omega-6 and lowering their omega-6:omega-3 ratio can provide a moderately better metabolic conversion of ALA to EPA and DHA. That's because high levels of omega 6 is a contributor to the decrease conversion levels of ALA to EPA and DHA.
Algae is the only vegetarian source that provides a meaningful DHA amount. Algal sources of DHA have recently become available which, when taken as supplements or via fortified foods such as DHA-enhanced soymilk, can provide a non-animal source of DHA. Such supplementation with DHA in vegetarian women is known to dramatically elevate DHA levels in breast milk within a short period of time.
Should we still eat flax seeds? Yes
Flax seeds provide much more than the richest source of ALA. Flaxseed is approximately 38% oil, which is comprised mainly of ALA, 28 % fiber (approximately two-thirds insoluble), 20% protein with an amino acid profile similar to soybeans; 7 % carbohydrates (simple sugars, lignans, phenolic acids and hemicellulose), 4% ash, 2% minerals (magnesium, potassium, calcium, iron, phosphorous, sodium, copper, zinc, manganese, selenium), 0.32% vitamins A, B1, B2, D, E, and niacin, 0.15% lecithin, 0.1 % flavonoids and 0.1% phytic acid.
Besides the omega-3 content, flax’s most beneficial compounds are likely its lignans and fiber. Lignans are phyto-estrogens – plant compounds that can have estrogen-like actions.
Through the actions of the lignans and ALA, flax blocks tumor growth in animals and may help reduce cancer risk in humans.
The major lignan in flax is is a powerful phytoestrogen chemically similar to the breast cancer drug tamoxifen. Postmenopausal women consuming 5 or 10 grams of milled flax over seven weeks showed significant reductions in blood concentrations of the most potent estrogen, estradiol, and its less potent sister, estrone. This may be desirable for postmenopausal women who have a high risk of breast cancer. This lignan is also a potent antioxidant – 500% more powerful than vitamin E!
These lignans have shown such extraordinary potential that they have been studied by the National Cancer Institute for their cancer-preventative properties. Studies have shown a substantial reduction in breast cancer and prosate cancer in people with high inakes of this lignan.
Flax has been shown to lower blood cholesterol levels and help reduce the risk of heart attacks and stroke, likely related to fiber content, but partly through the actions of ALA, which may be especially important to vegetarians and people with low intakes of fatty fish.
In a cohort of more than 45,000 U.S. men followed for 14 years, each 1g/day increase in dietary ALA intake was associated with a 16% reduction in the risk of heart disease. In a cohort of more than 76,000 U.S. women followed for 10 years, those with the highest ALA intakes (approx. 1.4 g/day) had a 45% lower risk of fatal heart disease than women with the lowest intakes (~0.7 g/day). Findings from the Health Professionals Follow-up Study of 45,722 men indicated that each gram of ALA in the daily diet was associated with a 47% lower risk of heart disease among men with low intakes of EPA and DHA (<100mg/d)
Flax’s soluble fibers also promote intestinal health and glycemic control.
So much for trying not to make this long! That's it for now but stay tuned for DHA content of specific foods and the safety of fish oil supplements!Sources: http://dhaomega3.org/ , http://www.chiroweb.com/columnist/maher/
