Maximizing Essential Fatty Acids in Vegetarian and Vegan Diets
Maximizing Essential Fatty Acids in
Vegetarian and Vegan Diets
by Brenda Davis, RD
Mahatma Gandhi once said, "Where ever flaxseeds become a regular food item among the people, there will be better health". While this prediction was based on simple observation, scientific evidence would suggest there is more than a grain of truth to his words. Flaxseeds are an exceptional source of lignans, a potent anticarcinogen and the richest known source of the essential omega-3 fatty acid, alpha-linolenic acid.
It is generally assumed that North Americans need not worry about getting enough fat of any kind, but as research unfolds, a serious flaw in this thinking is revealed. Not all fats are damaging to health. Some fats are protective, and two in particular are essential to life – they are the essential fatty acids (EFA), linoleic acid (LA)(omega-6) and alpha-linolenic acid (ALA)(omega-3).
Changes in our food supply since the industrial revolution have jeopardized both the quantity and balance of these nutrients. Our current dietary pattern provides excessive amounts of omega-6 fatty acids in relation to omega-3 fatty acids.1,2 This imbalance of essential fatty acids affects vegetarians and vegans at least as much as omnivores. In addition, the trend towards very low fat vegetarian or vegan diets (10% or less of calories from fat) may further compromise essential fatty acid intake.
Function of Essential Fatty Acids
Essential fatty acids are necessary for the formation of healthy cell membranes, the proper development and functioning of the brain and nervous system, and for the production of hormone-like substances called eicosanoids (thromboxanes, leukotrienes, prostaglandins, prostacyclins). These chemicals regulate numerous body functions including blood pressure, blood viscosity, vasoconstriction, immune and inflammatory responses.3 Humans have the ability to convert linoleic and alpha-linolenic acid to longer chain fatty acids, which serve as precursors for eicosanoids.
Eicosanoids formed from arachidonic acid (AA) (omega-6 family) have the potential to increase blood pressure, inflammation, platelet aggregation, thrombosis, vasospasm, allergic reactions and cell proliferation. Those formed from eicosapentanoic acid (EPA)(omega-3 family) have opposing affects.4,5 Omega-6 and omega-3 fatty acids are not interchangeable; we must consume both.
These two families of essential fatty acids compete for enzymes involved in their desaturation, thus the excessive consumption of foods rich in omega-6 fatty acids may compromise the conversion of alpha-linolenic acid to EPA, with adverse affects for health and disease. Current research suggests that the levels of essential fatty acids and the balance between them may play a critical role not only in growth and development, but also in the prevention and treatment of chronic diseases including coronary artery disease, hypertension, type II diabetes, arthritis and other immune/inflammatory disorders, and cancer.6-11
The primary sources of essential fatty acids are plants on land and in the sea. Linoleic acid is found primarily in seeds, nuts, grains and legumes. Alpha-linolenic acid is found in the green leaves of plants, including phytoplankton and algae, and in selected seeds, nuts and legumes (flax, canola, walnuts and soy). Arachidonic acid (AA) and docosahexaenoic (DHA) acid are obtained directly from animal foods – AA from meat and poultry and DHA and EPA from fish.
When addressing the issue of essential fatty acids in vegetarian and vegan diets, three key questions arise:
1. How much omega-6 and omega-3 fatty acids do vegetarian and vegans need?
2. Do vegetarian and vegans convert alpha-linolenic acid to EPA and DHA in sufficient quantity?
3. How can vegetarian and vegans insure an adequate intake of omega-3 fatty acids?
How much omega-6 and omega-3 do vegetarian and vegans need?
There are two primary considerations when assessing the adequacy of these essential fatty acids: quantity and balance. The 2003 Joint WHO/FAO Expert Consultation on Diet, Nutrition and the Prevention of Chronic Diseases recommends 5–8% of calories from omega-6 fatty acids and 1–2% of calories from omega-3 fatty acids.12 This provides a ratio of omega-6 fatty acids relative to omega-3 fatty acids of 2.5:1 to 8:1. The Institute of Medicine established adequate intakes (AI) for essential fatty acids, based on current average intakes. The adequate intakes for LA are 12 g/day for women and 17 g/day for men. The adequate intakes for ALA are 1.1 grams a day for women and 1.6 g/day for men.13 These AI’s provides a ratio of omega-6 fatty acids relative to omega-3 fatty acids of approximately 10-11:1. Both sets of recommendations are meant for the general population, and assume some direct intake of EPA and DHA. For vegetarians and vegans who consume little if any direct sources of EPA and DHA, smaller ratios have been suggested to help maximize conversion of alpha-linolenic acid to EPA and DHA. Researchers have found maximal conversion to both EPA and DHA with omega-6:omega-3 ratio ratios ranging from 2:1 to 4:1.14,15 To achieve this ratio in vegetarian and vegan diets, omega-6 fatty acids could be maintained at 5-8 percent of calories and omega-3 fatty acids adjusted up to1.25-2.5% of calories.
Those with increased needs for EPA/DHA (e.g. pregnant and lactating women), or those who are at greater risk for poor conversion (people with diabetes, hypertension or neurological disorders associated with low omega-3 status, and the elderly) may be well advised to aim for the higher end of this range (2-2.5% of calories). It may also be prudent to include an EPA/DHA supplement for some individuals.While it is not common, it is possible to over-consume omega-3 fatty acids. If a person minimizes omega-6 fatty acids and uses large amounts of omega-3-rich foods resulting in a ratio of omega-6: omega-3 of less than 1:1, insufficient LA conversion to HUFA can occur.
Are plant sources of omega-3 sufficient for human needs?
Vegetarians and vegans have few direct sources of EPA and DHA in the diet thus must convert ALA to EPA and DHA in the body.While conversion of essential fatty acids to longer chain fatty acids is, at least in part, dependent on genetics, age, and overall health, several dietary factors also have a significant impact on the conversion process. First, it is important to assure that the diet is nutritionally adequate, as poorly designed diets can depress conversion. Insufficient energy or protein decreases the activity of conversion enzymes, as can deficiencies of pyridoxine, biotin, calcium, copper, magnesium and zinc.6,16 Trans fatty acids can also depress conversion enzymes, and competitively inhibit the incorporation of essential fatty acids into cell membranes. In addition, alcohol inhibits the activity of delta-5 and delta-6 desaturase and depletes tissues of long-chain omega-3 fatty acids.17 High intakes of omega-6 fatty acids can have a profound effect on omega-3 fatty acid conversion, reducing it as much as 40 percent.18 Conversion enzymes may also be compromised in people with diabetes or certain metabolic disorders, and those who inherit a limited ability to produce these enzymes (possibly where fish has been a major component of the diet for generations).19
While conversion of LA to AA is typically efficient, conversion of ALA to EPA and DHA tends to be less efficient. In healthy individuals, an estimated 5-10 percent of alpha-linolenic acid is converted to EPA, but < 2-5 percent to DHA. 18, 20, 21 Preliminary evidence suggests that conversion may be significantly better in women than men. Two recent UK studies found that young men converted ALA at a rate of approximately 8 percent to EPA and 0 percent to DHA, while young women converted 21 percent of ALA to EPA and 9 percent to DHA.22, 23
Although conversion is slow and incomplete, it appears to be adequate to meet the needs of most healthy people, if intake of ALA is sufficient.24 It is important to note that there is a rapidly expanding data base that demonstrates significant effects of omega-3 fatty acids on primary and secondary prevention of chronic diseases, particularly cardiovascular disease. Both epidemiologic and randomized controlled clinical studies have evaluated the effects of both marine and plant sources of omega-3 fatty acids from food sources as well as supplements. These studies have established that both forms of omega-3 fatty acids have protective effects.25
How can vegetarians and vegans ensure an adequate intake of omega-3?
There are four important steps vegetarians and vegans can take to help improve omega-3 fatty acid status:
- Include good sources of alpha-linolenic acid in the daily diet. The very best sources of alpha-linolenic acid are flaxseeds, flaxseed oil, hempseeds, hempseed oil, canola oil, walnuts and green leafy vegetables. Aim for 1.25-2.5% of calories as omega-3 fatty acids. For most adults this amounts to 3 to 5 grams per day. Flaxseeds are by far the richest common source of ALA at 57 percent. One teaspoon of flaxseed oil or one and a half tablespoons of ground flaxseed, plus your usual intake of vegetables, walnuts and other foods provides plenty of omega-3 fatty acids for most people. Table 1 provides the EFA content of selected plant foods.
Table 1: EFA Content Selected Plant Foods
|
FOOD/serving size
|
ALA
%
|
LA
%
|
n-6:n-3 Ratio
|
ALA
g/serving
|
LA
g/serving
|
|
Flaxseed oil, 1 Tbsp.
|
57
|
16
|
0.28:1
|
8.0
|
1.6
|
|
Flaxseed, whole, 2 Tbsp.
|
57
|
16
|
0.28:1
|
5.0
|
1.4
|
|
Flaxseed, ground, 2 Tbsp.
|
57
|
16
|
0.28:1
|
3.6
|
1.0
|
|
Greens (mixed), 1 c
|
56
|
11
|
0.19:1
|
0.1
|
.03
|
|
Hempseed oil, 1 Tbsp.
|
19
|
57
|
3:1
|
2.7
|
8.0
|
|
Hempseeds, 2 Tbsp.
|
19
|
57
|
3:1
|
1.0
|
3.0
|
|
Walnuts, 1 oz (1/4 c)
|
14
|
58
|
4:1
|
2.6
|
5.4
|
|
Canola oil, 1 Tbsp.
|
11
|
21
|
2:1
|
1.6
|
3.2
|
|
Soybean oil, 1 Tbsp.
|
7
|
51
|
7:1
|
0.9
|
7.0
|
|
Soybeans, 1 c cooked
|
7
|
50
|
7:1
|
1.0
|
7.8
|
|
Tofu, firm ½ c (4.5 oz)
|
7
|
50
|
7:1
|
0.7
|
5.0
|
- Moderate the use of oils rich in omega-6 fatty acids, and high-fat processed foods rich in these oils. While increasing omega-3 fatty acids is an important first step in correctly EFA imbalance, vegetarians and vegans with high omega-6 intakes may be well advised to moderate their omega-6 intake. The best way of doing this, without compromising nutrient intake, is to reduce use of omega-6-rich/omega-3 poor oils and processed foods containing large amounts of these oils. Sunflower, safflower, corn, grapeseed, soybean and cottonseed oils contain the greatest amounts of omega-6 fatty acids, relative to omega-3 fatty acids. While hempseed and walnut oils are rich in omega-6 fatty acids, they are beautifully balanced with omega-3 fatty acids, so are good options. Omega-6-rich whole foods such as sunflower seeds, pumpkin seeds, sesame tahini, soybeans and wheat germ are highly nutritious plant foods, thus can be enjoyed as part of a varied plant-based diet.
- Make the primary dietary fat monounsaturated, if consuming more than 15 percent of calories from fat. When dietary fat is less than 15 percent of total calories, polyunsaturated fats should predominate. If fat intake is higher, generally monounsaturated fatty acids should be present in the largest quantity. When monounsaturated fats become the primary dietary fat, saturated fats, trans fatty acids and omega-6 fatty acids are kept in check, and the balance of omega-6 to omega-3 fatty acids improves. Fats in the following foods contain primarily monounsaturates: nuts (except for walnuts and butternuts), peanuts, olive oil, olives, avocados, canola oil, high-oleic sunflower and high-oleic safflower oils. Whole foods rather than oils are the preferred sources of monounsaturated fat
sbecause they contribute many other nutrients, fiber and phytochemicals to the diet.
- Consider including a direct source of EPA and/or DHA in the diet. Individuals at risk for poor EFA conversion, and those with increased EFA needs may benefit from direct sources of EPA and DHA. The primary sources of EPA and DHA are fish and seafood. Thus, for vegetarians and vegans, increasing consumption of these long-chain omega-3 fatty acids can be a challenge. For lacto-ovo vegetarian and vegans, eggs provide a reasonable amount of DHA (approximately 50 mg/egg), although very little EPA. Most supermarkets also sell DHA-rich eggs, providing 2-3 times the DHA of conventional eggs. Eggs from chickens fed flax generally provide 60-100 mg DHA per egg, while those from chickens fed microalgae contain 100-150 mg DHA per egg. The only plant sources of long-chain omega-3 fatty acids are plants of the sea – microalgae and seaweed. Macroalgae, otherwise known as seaweed, is even lower in fat than most vegetables (<1-14 percent of calorie s from fat), although it does contain small amounts of long-chain omega-3 fatty acids. A 100 gm serving provides, on average, about 100 mg of EPA, but little DHA. Seaweeds do not contribute significantly to EPA intakes in the Western world, but are sources where people use large quantities of seaweed on a daily basis (e.g. Japan and other parts of Asia). Very large intakes of seaweeds are not recommended, as it may contain excessive amounts of iodine. For example, just one gram of dried kelp contains about 3000 mcg of iodine. The upper limit to avoid toxicity is 1100 mcg. Microalgae is the most promising source of long-chain omega-3 fatty acids for people who do not consume fish. One variety, which provides 10-40 percent DHA by dry weight, is currently available in supplement form. When supplementing with a direct DHA source, 100-300 mg/day is recommended (look for veg caps). EPA-rich microalgae is also now being used in one type of vegan supplement from the UK. This supplement offers a mix of EPA and DHA. Blue-green algae (spirulina and aphanizomenon flos aquae) are low in long-chain omega-3 fatty acids. Spirulina is rich in gamma-linolenic acid (GLA – an omega-6 fatty acid), while aphanizomenon flos aquae (AFA) is more concentrated in ALA. While blue-green algae is not a significant source of EPA or DHA, some research indicates that it has a very high conversion rate in comparison to other plants.26 Thus, while vegetarian and vegans can rely on eggs and/or microalgae supplements for DHA, most consume little, if any EPA. However, approximately 10-11 percent of DHA is retroconverted back to EPA, thus if sufficient ALA and DHA are consumed, total EPA production would be expected to be adequate.27
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