My friend Daniel Patterson, the chef and owner of Coi in San Francisco, recently told me that some of his meat suppliers have been promoting grass-fed beef as a good source of healthful omega-3 fatty acids, both the linolenic acid found in walnuts and canola oil, and the very long chain fatty acids characteristic of fish oils. Beef, the archetype of foods laden with cholesterol-raising saturated fats, as a health food? I took a fresh look at the numbers.
Sure enough, grass-fed beef has substantially more omega-3 fatty acids than conventional beef raised on grain or a combination of grain and other concentrated nutrients. This makes sense: green grass doesn’t have much fat or oil, but its membranes are rich in linolenic acid. When the grass is cut and turned into hay, the linolenic acid tends to be oxidized and converted into other molecules, so hay is a poorer source, and grains contain little or no linolenic acid.
Once it gets into cattle, the grass linolenic acid meets several fates. Much of it is hydrogenated by microbes in the animal’s rumen, and turned into more saturated, less valuable fatty acids. Some of it enters intact into the circulation, and ends up being deposited in both muscle and milk. And a small portion of it is converted by the cattle tissues into the longer-chain fatty acids found in abundance in fish.
So is grass-fed beef a meaningful source of omega-3s? No. An entire grass-fed beefsteak contains hundredths of a gram of long-chain omega-3s, and less than a quarter of a gram of linolenic acid. You can get the same quantities from a couple of walnut pieces and a few grams—a very small bite—of salmon or oyster. Beef is wonderful stuff, and grass-fed beef is especially lean and flavorful, but it’s still beef.
Dannenberger, D. et al., J. Agric. Food Chem. 2004, 52 (21) 6607