A REPORT published today by the Union of Concerned Scientists, an environmental group, confirms that meat and the milk from cows fed only grass have higher levels of omega-3's, beneficial fatty acids, than meat and milk from cows raised conventionally, on grain. Omega-3's may prevent heart disease and bolster the immune system.
But the report, "Green Pastures," which examined all the available scientific literature, found no human studies suggesting that conjugated linoleic acid or C.L.A., higher in some grass-fed food, is beneficial.
There is little argument that grass-fed steaks and ground beef are almost always lower in fat than those from cattle raised conventionally. But according to the author of the report, Kate Clancy, a senior scientist at the Union of Concerned Scientists, steak from grass-fed cattle also has higher levels of omega-3 fatty acids than steak from cattle raised conventionally. Milk from grass-fed cows also tends to have higher levels of one of the omega-3's.
But for C.L.A., another omega fatty acid, Dr. Clancy said, human studies do not exist. There are more than 750,000 Web sites promoting the benefits of C.L.A., including its ability to reduce the risk of breast cancer, decrease body fat and enhance the immune system.
"C.L.A. is a very interesting phenomenon as a fatty acid and the animal findings are unbelievable," Dr. Clancy said on Monday. "But the research on the human side has not caught up."
Her study pointed out that consumers have lower exposure to antibiotics when they eat grass-fed animals. Conventionally raised animals are routinely given antibiotics to promote growth and prevent disease while those that are grass-fed receive only therapeutic doses.
The report also discusses environmental benefits from raising animals on grass instead of on grain requiring fertilizers and pesticides: less soil erosion and improved water quality. And there are economic advantages: more profit per animal for producers.
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