Tuesday, February 9, 2010
Omega-3 Fats: An Essential Contribution
What makes omega-3 fats special? They are an integral part of cell membranes throughout the body and affect the function of the cell receptors in these membranes. They provide the starting point for making hormones that regulate blood clotting, contraction and relaxation of artery walls, and inflammation. They also bind to receptors in cells that regulate genetic function. Likely due to these effects, omega-3 fats have been shown to help prevent heart disease and stroke, may help control lupus, eczema, and rheumatoid arthritis, and may play protective roles in cancer and other conditions.
Omega-3 fats are a key family of polyunsaturated fats. There are three main omega-3s:
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) come mainly from fish, so they are sometimes called marine omega-3s.
Alpha-linolenic acid (ALA), the most common omega-3 fatty acid in most Western diets, is found in vegetable oils and nuts (especially walnuts), leafy vegetables, and some animal fat, especially in grass-fed animals. The human body generally uses ALA for energy, and conversion into EPA and DHA is very limited.
The strongest evidence for a beneficial effect of omega-3 fats has to do with heart disease. These fats appear to help the heart beat at a steady clip and not veer into a dangerous or potentially fatal erratic rhythm. (1) Such arrhythmias cause most of the 500,000-plus cardiac deaths that occur each year in the United States. Omega-3 fats also lower blood pressure and heart rate, improve blood vessel function, and, at higher doses, lower triglycerides and may ease inflammation, which plays a role in the development of atherosclerosis.
(1)Several large trials have evaluated the effect of fish or fish oils on heart disease. In the Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardio (known as the GISSI Prevention Trial), heart attack survivors who took a 1-gram capsule of omega-3 fats every day for three years were less likely to have a repeat heart attack, stroke, or die of sudden death than those who took a placebo. (2) Notably, the risk of sudden cardiac death was reduced by about 50 percent. In the more recent Japan EPA Lipid Intervention Study (JELIS), participants who took EPA plus a cholesterol-lowering statin were less likely to have a major coronary event (sudden cardiac death, fatal or nonfatal heart attack, unstable angina, or a procedure to open or bypass a narrowed or blocked coronary artery) than those who took a statin alone.
(3)Most Americans take in far more of another essential fat—omega-6 fats—than they do omega-3 fats. Some experts have raised the hypothesis that this higher intake of omega-6 fats could pose problems, cardiovascular and otherwise, but this has not been supported by evidence in humans. (4) In the Health Professionals Follow-up Study, for example, the ratio of omega-6 to omega-3 fats wasn't linked with risk of heart disease because both of these were beneficial. (5) Many other studies and trials in humans also support cardiovascular benefits of omega-6 fats. Although there is no question that many Americans could benefit from increasing their intake of omega-3 fats, there is evidence that omega-6 fats also positively influence cardiovascular risk factors and reduce heart disease.
Researchers are taking a hard look at a different sort of balance, this one between possible effects of marine and plant omega-3 fats on prostate cancer. Results from the Health Professionals Follow-up Study and others show that men whose diets are rich in EPA and DHA (mainly from fish and seafood) are less likely to develop advanced prostate cancer than those with low intake of EPA and DHA. (6) At the same time, some-but not all-studies show an increase in prostate cancer and advanced prostate cancer among men with high intakes of ALA (mainly from supplements). However, this effect is inconsistent. In the very large Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, for example, there was no link between ALA intake and early, late, or advanced prostate cancer.
(7)Here's a delicious way to get your omega-3s: Try Pan Roasted Salmon with Minty Snap Peas.
Given the wide-ranging importance and benefits of marine omega-3 fatty acids, it is important to eat fish or other seafood one to two times per week, particularly fatty (dark meat) fish that are richer in EPA and DHA. This is especially important for women who are pregnant or hoping to become pregnant and nursing mothers. From the third trimester until the second year of life, a developing child needs a steady supply of DHA to form the brain and other parts of the nervous system. Many women shy away from eating fish because of concerns that mercury and other possible contaminants might harm their babies, (9) yet the evidence for harm from lack of omega-3 fats is far more consistent, and a balance of benefit vs. risk is easily obtained.
1. What are omega-3 fatty acids, and why should I make sure to include them in my diet?
Omega-3 fatty acids (also known as n-3 fatty acids) are polyunsaturated fatty acids that are essential nutrients for health. We need omega-3 fatty acids for numerous normal body functions, such as controlling blood clotting and building cell membranes in the brain, and since our bodies cannot make omega-3 fats, we must get them through food. Omega-3 fatty acids are also associated with many health benefits, including protection against heart disease and possibly stroke. In addition to these established benefits for cardiovascular disease, omega-3 fatty acids in high doses (e.g 6 to 10 capsules per day) are used to treat depression. New studies are identifying potential benefits for a wide range of conditions including cancer, inflammatory bowel disease, and other autoimmune diseases such as lupus and rheumatoid arthritis.
2. What foods are good sources of omega-3 fatty acids? How much do I need to eat of these foods to get enough omega-3s?
There are two major types of omega-3 fatty acids in our diets: One type is alpha-linolenic acid (ALA), which is found in some vegetable oils, such as soybean, rapeseed (canola), and flaxseed, and in walnuts. ALA is also found in some green vegetables, such as Brussels sprouts, kale, spinach, and salad greens. The other type, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), is found in fatty fish. The body partially converts ALA to EPA and DHA.
We do not know whether vegetable or fish omega-3 fatty acids are equally beneficial, although both seem to be beneficial. Unfortunately, most Americans do not get enough of either type. For good health, you should aim to get at least one rich source of omega-3 fatty acids in your diet every day. This could be through a serving of fatty fish (such as salmon), a tablespoon of canola or soybean oil in salad dressing or in cooking, or a handful of walnuts or ground flaxseed mixed into your morning oatmeal.
3. What are omega-6 fatty acids? Should I be concerned about the ratio of omega-6 fatty acids to omega-3 fatty acids in my diet?
Omega-6 fatty acids (also known as n-6 fatty acids) are also polyunsaturated fatty acids that are essential nutrients, meaning that our bodies cannot make them and we must obtain them from food. They are abundant in the Western diet; common sources include safflower, corn, cottonseed, and soybean oils.
Omega-6 fatty acids lower LDL cholesterol (the "bad" cholesterol) and reduce inflammation, and they are protective against heart disease. So both omega-6 and omega-3 fatty acids are healthy. While there is a theory that omega-3 fatty acids are better for our health than omega-6 fatty acids, this is not supported by the latest evidence. Thus the omega-3 to omega-6 ratio is basically the "good divided by the good," so it is of no value in evaluating diet quality or predicting disease.
4. Is it better to get omega-3 fatty acids from food or from supplements?
Certainly foods, since the plants and fish that contain omega-3 fats have other good nutrients, such as protein, vitamins and minerals. People who do not eat fish or other foods rich in omega-3 fatty acids should consider taking an omega-3 supplement of 500 mg per day; fish oil is used in supplements, but there are also vegetarian supplements that have ALA. Studies suggest that people who have already had a heart attack may benefit from higher doses of omega-3 supplements (basically, double the 500 mg), so if you do have heart disease, consult your healthcare provider about whether taking a higher dose of omega 3s makes sense for you.
5. I am a vegetarian, so I do not consume any fish. But I get plenty of ALA in my diet, from canola and soybean oil, ground flax seed, and walnuts. How efficiently does the body convert ALA to DHA and EPA? Should I take an algal DHA supplement?
If you are getting adequate ALA in your diet from oils and nuts, I am not sure you really need to take an algal DHA supplement. As I mentioned above, the body partially converts ALA to EPA and DHA; it is not known if ALA has substantial health benefits as is, or whether it must be converted to EPA and DHA to produce most of the benefits. My current interpretation of the science is that ALA has direct health benefits, through its role in reducing inflammation and protecting the heart against arrhythmias, and it also has indirect health benefits, through its conversion to EPA and DHA.
6. Can omega-3 fatty acids be destroyed by high-heat cooking?
Not if the oil is fresh. In fact, even in frying oil that is used for days, you still can find ALA in it.
Reference http://www.hsph.harvard.edu By Dr. Frank Sacks