Throughout most of human history, our ancestors ate a diet that was nearly perfect in its balance between two essential fatty acids, omega-3s and omega-6s, which have crucial, though opposite, roles to play in metabolism.
In the last few decades, however, this delicate balance has been thrown out of whack, with most of us eating too many omega-6s, which come chiefly from corn and safflower oils, and far too few omega-3s, found in fatty, cold-water fish such as salmon and tuna as well as walnuts, canola, soy and flax seed oil. This nutrient imbalance is believed to contribute to arthritis, cystic fibrosis, heart attacks and other diseases.
“We are drowning in omega-6 relative to omega-3’s,” says Dr. George L. Blackburn, associate director of nutrition in the Division of Nutrition at Harvard Medical School. Throughout evolution, the ratio of omega-6 to omega-3 was two 6’s to one 3, he says. “Now it’s about 20 to one. We have wiped out a lot of sources of omega-3 and have a huge intake of omega-6-heavy products like corn and safflower oils.”
“We need some of both,” adds Dr. Walter Willett, chair of the department of nutrition at the Harvard School of Public Health. The goal is to bring back a balance “by increasing omega-3s, not by decreasing omega-6s.”
Omega-6 fatty acids get converted in the body to substances that rev up the immune system and inflammatory response – a good thing for fighting infections, but detrimental in people prone to auto-immune problems such as arthritis. Omega-6s also boost clotting – a benefit if you’re bleeding to death, but potentially harmful in terms of increasing clots that can lead to heart attacks or strokes.
“We have doubled omega-6s in our food supply in the last 40 years” says Willett. “That’s one of the most important reasons that heart disease mortality has declined by 50 percent since the 1950s…Omega-6 lowers cholesterol and has some benefits on platelets and anti-arrhythmic effects as well….We need the 6s. We don’t want to reduce those.”
Omega-3s, by contrast, get converted in the body to substances that decrease the immune response, a benefit for people with auto-immune problems, and increase the time it takes for blood to clot, a benefit for people at risk of heart disease. Omega-3’s also decrease potentially fatal cardiac arrhythmias and are crucial to the healthy development of the spinal cord, brain and retina in infants and to healthy brain functioning in older people as well.
Because Americans are relatively deficient in omega-3s, doctors and scientists are now scrambling to find ways to increase omega-3s in our diet.
Last week, researchers at Massachusetts General Hospital announced that they had genetically altered mice to produce omega-3 fatty acids. Scientists from Beth Israel Deaconess Medical Center and UMass Memorial Medical Center in Worcester also reported on research that suggests that people with cystic fibrosis may be helped by increasing omega-3s.
Later this month, the Institute of Medicine, an arm of the National Academy of Sciences, is expected to issue a report evaluating the methods used to assess the safety of additives to infant formula, including DHA, an omega-3 fatty acid, and AA, an omega-6. European countries have long added DHA and AA to baby formulas; American manufacturers began doing so two years ago to bring formulas closer to the composition of breast milk.
Because there are now so many products, particularly dietary supplements, out there in health food stores, supermarkets and pharmacies, it’s worth taking a moment to understand the terminology on product labels and ads.
There are many kinds of omega-6 fatty acids, and the one people need to consume in the diet – that is, the “essential” fatty acid – is linoleic acid. This gets converted in the body to arachidonic acid (AA) (which cannot be obtained from the diet) and which boosts the immune system and clotting by increasing a hormone called prostaglandin E2.
There are also many kinds of omega-3 fatty acids, the most important of which are DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), both of which are found in fish. DHA can also be made by the body from its precursor, an omega-3 called linolenic acid, which comes from soy, canola, walnut and flaxseed. EPA can also be made from linolenic acid. The body’s biochemical machinery uses these acids to make prostaglandin E1, which slows down the immune system and increases the time it takes for blood to clot.
Omega-6 and omega-3 are both in the family of “PUFAS,” or polyunsaturated fatty acids. Fatty acids are long chains of carbon atoms hooked to each other and linked hydrogen bonds. If there are no “double bonds” between carbons, the fat is said to be saturated. If there is a “double bond” anywhere in this chain, the fat is unsaturated. If there are lots of double bonds, the fat is polyunsaturated.
Polyunsaturated fats are considered “good” because every double bond causes a 37 degree kink in the chain, which makes the fat more fluid. That in turn makes it easier for the fat to do one of its major jobs, slink into the fatty membrane around cells.
Because omega-3 fatty acid suppresses immune function and increases the time it takes for blood to clot, one might think that an excess could lead to an increase in infections and bleeding problems. This does not appear to be the case. “We’re not even close to those dangers – maybe the Eskimos are,” says Dr. Ernst Schaefer, chief of the lipid metabolism laboratory at the Human Nutrition Research Center at Tufts University.
The bottom line? Don’t stop eating omega-6 oils, but increase omega-3 however you can. This means eating more fish – yes, even salmon despite the risk of pollutants such as mercury, dioxin or PCBs. It also means breastfeeding if you can, or choosing formulas containing DHA and AA if you can’t.
If you hate fish, try taking 1 gram a day of fish oil supplements containing omega-3 fatty acids. But beware: Fish oil capsules vary greatly in quality. To reduce the chance that the supplements have the same pollutants as in fish, it may be wise to stick with well-known national brands.