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A recent study comparing the kinds of fat in organic and conventional full-fat milk concluded that, by drinking organic milk, consumers could help reduce or eliminate "probable risk factors for a wide range of developmental and chronic health problems."
The benefit was attributed to the quantity of two kinds of fats, omega-6 and omega-3, and the ratio between them. The research paper made the case that there are health benefits to lowering the ratio — decreasing omega-6 intake and increasing omega-3 — and that drinking organic milk helps do that.
Largely funded by the organic milk industry and published in December in the journal PLOS One, the study was heralded as evidence that organic whole milk has a heart-healthy fat profile, primarily because it contains higher omega-3 levels than conventional milk. Do the math, though, and you'll find that you would have to drink 51 / 2 gallons of full-fat organic milk to equal the omega-3 content of one eight-ounce piece of salmon.
There are good reasons to buy organic dairy. USDA organic standards require that the cows graze outdoors, on pasture, for as long as the grazing season allows, that they be kept in uncrowded conditions with opportunity to exercise and that their manure be managed to avoid contaminating soil, water or crops. The animals also are raised without antibiotics, a practice that reduces the risk of antibiotic-resistant infections in humans.
But the idea that the fat profile of organic milk makes it a better choice for broad health reasons than conventional milk is difficult to support.
At issue, first, is the evidence for the importance of the two kinds of polyunsaturated fats — omega-6 and omega-3 — and the ratio between them.
Omega-6 fats come primarily from vegetable oils and are essential to normal body functioning, but high levels of them may promote inflammation, which is linked to heart disease and other health problems.
Omega-3s come in two flavors: long-chain and short-chain. Long-chain omega-3 fatty acids — eicosapentaenoic (EPA), docosapentaenoic (DPA) and docosahexaenoic (DHA) — come mainly from fish and are generally associated with lower disease risk. The primary short-chain omega-3 is alpha-linolenic acid (ALA), which comes from plant sources such as walnuts and flax, and is converted by the body to long-chain. Experts generally believe it to be less important because only a small part of the ALA we eat gets converted.
Because omega-6 and omega-3 fats are metabolized by the same enzyme, some experts theorize that when high levels of omega-6 fats hog that enzyme, there's not enough of it to convert ALA to long-chain omega-3s. Although some studies support the importance of the ratio, many health authorities are skeptical
Alice H. Lichtenstein, director of the Cardiovascular Nutrition Laboratory at the Research Center on Aging at Tufts University, says, "The bulk of the evidence suggests the absolute amount of omega-3 fatty acids, rather than the omega-6/omega-3 ratio," is what correlates to better health.
Three reviews of the importance of the ratio in cardiovascular disease, published in different journals, concluded that "the ratio is, both on theoretical and evidential grounds, of little value," that it is "not a useful concept" and that it is "of no value in modifying cardiovascular disease risk."
Dariush Mozaffarian, an associate professor of medicine and epidemiology at the Harvard School of Public Health, says that the evidence for the ratio's importance just isn't there: "One cannot find any series of systematic evidence from human studies that shows that the 'ratio' is significantly associated with poor health outcomes when omega-3 levels are high — i.e., when the 'ratio' is not simply driven by low omega-3s."
The milk study does not provide conclusive evidence of the ratio's importance. Of the 19 studies referenced to back up the health claims about the ratio, only a few showed a direct correlation between a lower ratio and a better outcome. Most others focused on omega-3 levels. One, which the study cited as evidence that a lower ratio decreases risk of diabetes, concludes that "Omega-6 and omega-6:omega-3 ratio were not associated with incidence of type 2 diabetes."
Charles Benbrook, lead author of the milk study, agrees that "there's no consistent pattern of whether the omega-6:omega-3 ratio is a statistically significant driver of health outcomes. In some studies it is, in some it isn't." He says that getting people to increase their intake of foods high in omega-3 fats is the better-supported goal, but he remains persuaded that lowering omega-6 fats at the same time, particularly if they are high to begin with, "is better than just increasing omega-3," given the issue of omega-6 hogging the enzyme necessary for the metabolization of omega-3.
The second issue with focusing on ratio is that, even if you accept that both strategies — increasing omega-3s and increasing omega-3s while decreasing omega-6s — are good for health, many foods allow you to do both more effectively than drinking many glasses of organic whole milk.
Of milk's omega-3 content, the study says, "based on recommended servings of dairy products and seafoods, dairy products supply far more ALA than seafoods, about one-third as much EPA, and slightly more DPA, but negligible DHA."
That suggests that dairy is almost as good a source of omega-3 fats as fish, but the critical phrase is "based on recommended servings." Because the federal government's Dietary Guidelines for Americans recommend three dairy servings per day but only eight ounces of fish per week, the paper compares 21 cups of organic milk (for a weekly total) to eight ounces of fish.
But a serving-for-serving comparison puts organic milk's fat profile in a different context. An eight-ounce glass of organic whole milk has 0.078 grams of omega-3s (compared with 0.048 for conventional milk), most of it ALA. An eight-ounce serving of salmon has 6.82 grams of omega-3s, or the amount in 88 cups of milk. Compare that milk to walnuts, a rich source of ALA, and you find that a one-ounce serving of shelled walnuts has 21 / 2 grams of ALA, which is as much as 21 / 2 gallons of organic milk.
(The U.S. Dietary Guidelines recommend that people stick to fat-free or low-fat milk and other dairy products, but such forms of milk have negligible amounts of omega-3 fats.)
A tablespoon of flaxseed has 2.3 grams of omega-3 fats. A dozen oysters have about a gram, depending on the variety. Two omega-3 eggs (from chickens fed high-omega-3 diets) can have over a gram.
Buying organic dairy products can safeguard the treatment of cows and encourage agricultural practices that benefit human and environmental health. And, although concerns about hormone, antibiotic and pesticide levels haven't been borne out by research, many consumers feel more comfortable with organic for that reason. But, if omega-3s are what you're after, there are better ways to get it than organic milk.
Haspel is a food and science writer. Follow her @TamarHaspel.