The world of fatty acids is a complicated one. There are saturated fats and unsaturated fats, trans-fats and hydrogenated fats, essential fatty acids, polyunsaturated and monounsaturated fats. First things first – let’s sort these out.
Fatty acids in general are long chains of carbon atoms bonded together with either single or double bonds and with or without hydrogen atoms. Different fats have different lengths of atom chains, different numbers of hydrogen atoms and different shapes. Small differences in structure translate into crucial differences in function. Fatty acids are generally not found singly in nature. They usually exist as three fatty acids in combination with glycerol in the form of triglyceride. Fatty acids can be saturated fats, trans-fats, mono-unsaturated fats or poly-unsaturated fats.
Saturated fats have no double bonds between their carbon atoms and all their bonds are filled up (saturated) with hydrogen. They are solid at room temperature and come from animal sources such as meat, poultry and dairy products as well as a few plant sources such as coconut oil, cocoa butter and palm oil.
Trans-fats exist in small amounts in nature but by far the most common trans-fats are those artificially produced through a process called hydrogenation. This process turns oils into solids and prevents them from becoming rancid. The process involves heating vegetable oil in the presence of hydrogen gas and a heavy-metal catalyst such as palladium to allow hydrogen atoms to be added to the carbon chain. On food label ingredient lists, this manufactured substance is typically listed as “partially hydrogenated oil.” Trans-fats are very unhealthy and should be completely avoided as much as possible.
Unsaturated fats include monounsaturated fats and polyunsaturated fats and are liquid at room temperature. Most vegetable oils are a mixture of polyunsaturated and monounsaturated fatty acids.
Monounsaturated fats have one double bond between two of their carbon atoms and are missing some hydrogen. Double bonds introduce bends in the fatty acid that influence the structure and physical properties of a fatty acid molecule. Sources of monounsaturated fats are olive oil, peanut oil, canola oil, soybean oil, sesame oil, avocados and nuts such as almonds, cashews and peanuts as well as high-oleic safflower and sunflower oils.
Polyunsaturated fats have multiple double bonds between their carbon atoms and are also missing some hydrogen. Polyunsaturated fats include omega-3 and omega-6 fatty acids which play important roles in the human body. Polyunsaturated fatty acids are an integral part of cell membranes, important for vision and for proper brain and nervous system function and act as chemical messengers for the cardiovascular and immune systems (6). Omega-6 polyunsaturated fatty acids are also mediators of growth and inflammation, blood vessel constriction and platelet aggregation (clotting) while omega-3 poly-unsaturated fatty acids are anti-inflammatory, anti-clotting, antiarrhythmic, lipid lowering and blood vessel relaxing. Deficiencies in essential fatty acid can cause abnormalities in the liver and kidneys, reduced rate of growth, decreased immune function, depression and dry skin (11). Studies indicate that omega-6 and omega-3 fatty acids can change the way that genes are expressed, especially those involved with fatty acid metabolism and inflammation (7,8)
Omega-3 and omega-6 fatty acids are called essential fatty acids (EFAs). They are “essential” because the human body requires them for good health but cannot synthesize them so they must be obtained from food. The two essential short-chain fatty acids are;
1 Omega-3 type fatty acid: Alpha-linolenic acid (ALA) which is metabolized into long-chain omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)
2 Omega-6 type fatty acid: Linoleic acid (LA) which is metabolized into long chain omega-6 fatty acids such as arachidonic acid (AA) and dihomo-γ-linolenic acid (DGLA) (6).
Omega-6 fatty acids
It is almost impossible to be low in omega-6 fatty acids. They are found in almost every food type – vegetable oils (such as corn, safflower, soybean, cottonseed, sesame, sunflower and olive oils), meats, dairy, eggs, nuts, seeds, leafy vegetables, legumes and grains. The amount of omega-6 fat required daily for human health is about 12 to 13 gm per day for women and 17 to 20 gm per day for men (1).
Whole plants contain far more fat than you might imagine. Here are some examples of the percentage of calories that comes from fat in plant foods (1,3).
|FOOD||% CALORIES FROM FAT|
|Broccoli, cauliflower, green pepper and asparagus||10%|
|Peas, lentils, beans||3%|
|Greens – spinach, kale||12% to 15%|
|Potatoes, sweet potatoes||1%|
|Peanuts, peanut butter||78%|
|Tree nuts (cashews, walnuts, brazil nuts, pecans, etc)||70%|
It is plain to see that if a person eats a variety of plant-based foods it is easy to consume enough fat. For example, calculating from a 2000 calorie plant-based diet with an average of 20% calories from fat a person would get 44 gm of total fat every day. Within this total fat, ample omega-6 fatty acids would be included. (The percentage of calories from fat in the standard Western diet is around 35%.)
Omega-3 fatty acids
Omega-3 fatty acids are not nearly as plentiful as omega-6s and so it is vital for humans to eat foods rich in omega-3 fatty acids every day. The amount of omega-3 fats required daily for human health is 1.1 gm for women and 1.6 gm for men (1,3).
The short-chain omega-3 fatty acid, ALA, can be found in many vegetables, beans, nuts, seeds and fruits. The best plant sources of ALA include flaxseeds, chia seeds, walnuts, wheat germ and oils such as canola, soybean, walnut and flaxseed oils. Corn, safflower, sunflower and cottonseed oils contain lower levels of omega-3s (11). Surprisingly half the fats in leafy greens are omega-3s. However, because greens are not high in fat, they are not a great source.
The best sources of long-chain omega-3s, DHA and EPA, are fatty fish, fish oil capsules, algae oil capsules or yeast-based omega-3 capsules.
Considerations about eating fish and fish oil for omega-3
The problem with regular consumption of fish is that it contains unhealthy contaminants – heavy metals such as mercury, persistent organic pollutants (POPs) and other environmental toxins (35,15,16), not to mention the potential health problems that come with eating animal protein. Because of these contaminants fish oil capsules may be better sources of pre-formed DHA and EPA than fish itself. Most fish oil supplements today do not contain the toxic heavy metal, mercury, because it can be removed during processing and purification (33). However, many still contain persistent organic pollutants (POPs) (34).
Another concern is the unstability of the omega-3s in fish oils, bringing up the possibility of the formation of free radicals and inflammation. ALA from plant sources such as nuts, seeds, beans, vegetables and fruits is present in a more stable form (18). More study on this aspect is needed to uncover its actual consequences, if any, to health (17).
Keep in mind that that fish do not produce omega-3s. They obtain them from their natural diet of plankton and other marine ingredients which contain the microalgae that actually produce omega-3s (21). As our beleaguered oceans are becoming depleted, farmed fish are evolving into a more important source of fish for food. The food that these fish eat is an important consideration if you are looking for omega-3s. You cannot obtain omega-3 from fish unless they are actually eating an omega-3 source themselves. Many fish farms have turned to inexpensive grain-sourced food which is full of omega-6 fatty acids, not omega-3s (31). If you are eating farmed fish, be sure you check out the omega-3 status of the fish food that your fish food ate.
Concerns about eating plants for omega-3
There is wide variability between people in their capacity to produce the long-chain omega-3 DHA from ALA, the extent of which has yet to be determined. Women, due to the effects of estrogen, can convert approximately 21% of dietary ALA to EPA and 9% to DHA while men convert approximately 8% of dietary ALA to EPA and up to 4% to DHA (6). Genetic variability also comes into play. It is thought that about 30% of the variance in blood levels of omega-3 and omega-6 fatty acids are due to genetic differences in the enzymes needed to produce long-chain omega-3s and omega-6s. Also, the action of these enzymes can be inhibited by too much dietary saturated fat and cholesterol and by deficiencies of some vitamins and minerals.
It appears that the conversion rate of ALA to DHA and EPA is greater in those eating a plant-based diet and that vegetarians readily convert ALA to DHA and EPA. The EPIC study showed that women on vegan diets have more long-chain omega-3s in their blood than fish-eaters, meat-eaters and lacto-ovo-vegetarians (19).
Considerations about taking algae oil or yeast-derived DHA capsules for omega-3
Microalgae are the organisms that actually produce omega-3 in the first place. As any fish would tell you if it could, microalgae are an excellent plant source of these healthy oils. They are an environmentally friendly and entirely renewable source that is free of contaminants (64). DHA from algae has been found to be 100% bioequivalent to the DHA in fish flesh (62). Yeast is a relatively new source of DHA (63).
The following are some good sources of omega-3 fatty acids (1,3);
|FOOD||SERVING SIZE||# GM OMEGA-3|
|Chia seeds,dried||1 tbsp||2.5|
|Flaxseeds, ground||1 tbsp||3.2|
|Canola oil, soybean oil||1 tbsp||0.8|
|Walnuts||1 ounce (28.35 gm)||2.6|
|Pacific herring||1.5 ounces||1|
|Salmon||2 to 3 ounces||1|
|Canned tuna, white||4 ounces||1|
|Rainbow trout||3.5 ounces||1|
Benefits of omega-3 fatty acids
The status of omega-3s and their effect on prevention of disease is in a state of flux at the present time. The following information might be confusing but the practical outcome is actually quite simple. Omega-3 fatty acids are very important for general health regardless of their status in disease prevention. Make sure you have a daily source and you can rest assured that your essential fat needs are taken care of.
Research into the relationship between long-chain omega-3s and cardiovascular disease has travelled a rocky road. Observational studies in the past consistently showed that higher consumption of fish and higher dietary or plasma levels of omega-3s were associated with lower risk of coronary disease and heart failure (58,59). Randomized controlled trials corroborated these findings using fish intake (38) and using fish oil capsules (39) as omega-3 sources. More recently however studies have become contradictory. Some conclude that omega-3s from supplements do not provide the same cardiovascular protection as those obtained from foods (9,10,22,23,24,25,26). Others show benefits from both omega-3 supplements and food sources (36,37,42,52,53,54,55,56,57). Theories for these discrepancies include the steep increase in the use of statin drugs which might blunt the benefits of omega-3 supplementation through the heart protection offered by these medications (23,41) or that there might be an upper limit of omega-3 above which there is no further benefit (40).
However the most recent meta-analysis, published January 31, 2018 and involving over 77,000 participants followed for more than four years, concludes that there is no significant association with supplementation of fish-derived omega-3 fatty acids and fatal or non-fatal coronary events. In other words, there is no supporting evidence that taking omega-3 supplements will prevent cardiovascular disease. (68). To strengthen this evidence, in August, 2018, a study from Great Britain found no significant difference in the risk of serious vascular events between those taking omega-3 fatty acid supplements and those who weren’t (69).
Cognition and brain function
Cognition and brain health is an area where omega-3s show promise of beneficial effects. Observational studies suggest that diets high in long-chain omega-3s can be associated with reduced risk of cognitive decline, Alzheimer’s disease and dementia (27,44). Randomized, controlled studies and meta-analyses confirm the benefit of contaminant-free long-chain omega-3 intake for improved brain function and reduced brain shrinkage in healthy older adults as well as decreased risk of dementia and Alzheimer’s Disease (30,45). However, once again results are not consistent. Many randomized trials do not show any benefit of fish intake in healthy older adults (46,29). In fact observable deficits in neurobehavioral performance have been observed. This may be due to neurotoxic contaminants such as mercury and PCBs from fish (28,29). In the final analysis researchers have come to the conclusion that increases in long-chain omega-3s through fish or supplements do not affect cognitive function in healthy older adults or people with Alzheimer’s Disease. For people with mild cognitive impairment, some aspects of cognition function, including attention, processing speed and immediate recall may be improved (47,48,49).
Pregnancy is an important time to ensure that adequate essential fatty acids are available as they are needed for proper growth and brain development of the fetus. Studies have shown that increased exposure to omega-3 while in the uterus and just after birth results in improved cognitive function and better vision that can be observed during the first few years of life (20,65,66,67). When a baby is breastfed, breast milk is the only source of essential fatty acids for that baby. Lactating mothers should make sure they are ingesting a good source of omega-3 fats.
Research is ongoing regarding the relationship between omega-3 fatty acids and the risk of cancer. Associations have been made for omega-3 fatty acids and decreased risk of breast cancer (13,14), while some other cancers seem to have increased risk with high omega-3 intake (61). Conclusive results remain to be seen.
Benefits of ALA itself
ALA, the short-chain omega-3 fatty acid, has also been studied for health benefits. Nine major studies using data gathered from large sample populations and over relatively long collection periods have found that high ALA tissue levels are associated with fewer cardiovascular events, strokes and cardiac death. Studies on high ALA diets show beneficial changes in cholesterol levels and types, reduction of triglycerides and lipoprotein(a), lower blood pressure and less inflammation (50). The need now is for randomized, controlled trials of dietary ALA sources such as flaxseed and their effects on subjects with symptoms of atherosclerotic heart disease.
The all-important ratio of omega-6 to omega-3
A crucial consideration regarding polyunsaturated fatty acids is the ratio between omega-6 and omega-3 fatty acids. Humans evolved eating approximately equal amounts of omega-6 and omega-3 fatty acids, a ratio of 1:1. The optimum ratio between omega-6s and omega-3s is between 1:1 and 4:1. Alarmingly, in most people eating the standard Western diet, this ratio is between 10:1 and 25:1. At this ratio any omega-3s available are completely overpowered by the huge amount of omega-6s that are flooding the system. Both fatty acids compete for the same enzymes in order to produce long-chain fatty acids. If one of them is at a dramatically lower concentration it will lose the competition (5). High omega-6 to omega-3 ratios are linked to numerous diseases, including cancer, heart disease and inflammatory conditions like arthritis (60). The level of inflammation in the body is markedly affected by the ratio between omega-6s and omega-3s (12). Higher concentrations of omega-3s can tip the balance to less inflammation (32). The main source of omega-6s today is from vegetable oils in our diet. One efficient way to improve your ratio? Cut back on vegetable oils.
Practical steps for good omega-3 status (51);
Include healthy sources of ALA in your daily food choices (flaxseeds, chia seeds, walnuts). One tablespoon of ground flaxseed daily in a smoothie or sprinkled onto cereal or a salad will easily supply enough ALA to provide your required omega-3s. Alternatively it can be sprinkled on a hot meal but wait until the cooking is over and the dish has cooled somewhat before adding your ground seeds. Heat can destroy omega-3s. It is important to grind flaxseed before eating it. Unground flaxseed can travel through the intestinal tract unchanged and its oil will remained locked inside the seed. Use a coffee or spice grinder and grind just before using. The shelf life of ground flaxseed is short although it can be frozen for longer storage. Chia seeds also benefit from grinding, although some of the oil from whole seeds will be liberated in the digestive tract.
Limit total fat intake, especially saturated and trans-fats. Use added oils sparingly. Avoid processed foods, full-fat dairy products and intake of tropical oils. If you must eat meat, do not eat it every day and consume only one serving that is smaller in size than a deck of cards.
If you use oil for cooking, use it very sparingly and stick to canola oil which has an omega-6 to omega-3 ratio of close to 2:1. Olive oil, a monounsaturated oil, can also be used although its ratio is 9:1. Also be aware that olive oil has a very low smoke point and should not be used for high-heat cooking.
Keep seeds that are low in omega-3 fatty acids down to less than 1 ounce a day. These include pumpkin, sesame and sunflower seeds. Avocados and most nuts (except for walnuts) should also be eaten in small amounts as they are high in omega-6s and very low in omega-3s.
Consider taking a direct source of DHA and EPA daily. A reasonable dose is 100 mg to 300 mg daily of DHA or DHA/EPA mix. DHA can be converted by the body to EPA so that DHA supplementation alone will lead to increased levels of both DHA and EPA. Fish oil capsules, algae oil capsules or yeast-sourced omega-3 capsules are all good DHA/EPA sources.
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