Omega-3 molecules are a by-product of the happy meeting of sunlight, water, and carbon dioxide in the chloroplasts of terrestrial plants and marine algae. Not long ago, these fatty acids were an inescapable component of our diet. Back in the early 1900s — long before the arrival of bovine growth hormone and patented transgenic seeds — American family farms were perfect factories for producing omega-3s.
Bucolic, sun-drenched pastures supported a complex array of grasses, and cattle used their sensitive tongues to pick and choose the ripest patches of clover, millet, and sweet grass; their rumens then turned the cellulose that humans can't digest into foods that we can: milk, butter, cheese, and, eventually, beef, all of them rich in omega-3s. Cattle used to spend four to five carefree years grazing on grass, but now they are fattened on grain in feedlots and reach slaughter weight in about a year, all the while pumped full of antibiotics to fight off the diseases caused by the close quarters of factory farms.
Likewise, a few generations ago, chickens roamed those same farms, foraging on grasses, purslane, and grubs, providing humans with drumsticks, breasts, and eggs that were rich in grass-derived omega-3s. Today, most American chickens are now a single hybrid breed — the Cornish — and are raised in cages, treated with antibiotics, and stuffed full of corn.
Our animal fats were once derived from leafy greens, and now our livestock are fattened with corn, soybeans, and other seed oils. (Even the majority of the salmon, catfish, and shrimp in our supermarkets are raised on farms and fattened with soy-enriched pellets.) So not only have good fats been stricken from our diets, but these cheap, widely available seed oils are the source of another, far less healthy family of fatty acids called omega-6s, which compete with omega-3s for space in our cell membranes. Omega-6s are essentially more rigid fatty acids that give our cells structure, while omega-3s are more fluid and help our bodies fight inflammation. Our ancestors ate a ratio of dietary omega-6s to omega-3s of approximately 1:1. The Western diet (the modern American and European eating pattern characterized by high intakes of red meat, sugar, and refined carbohydrates) has a ratio of about 20:1.
"The shift from a food chain with green plants at its base to one based on seeds may be the most far reaching of all," writes Michael Pollan in his prescriptive manifesto In Defense of Food.
This shift began in earnest in the 1960s. Research on the links between cholesterol and saturated fats and coronary heart disease led health authorities to demonize lard, dairy products, and other animal-derived sources of fat. Meanwhile, new health guidelines lionized the polyunsaturated fats in vegetable oils and margarine (which is merely vegetable oil solidified via hydrogenation, a process that creates the dreaded trans fats).
Food processors were happy to play along: Polyunsaturated seed oils did not go rancid as quickly as omega-3s, which meant a longer shelf life for packaged foods. One form of fat in particular, omega-6-rich soybean oil, is now ubiquitous in processed foods. Soybeans, originally an import from East Asia, have become the second most valuable food crop in the United States. Genetically modified to resist pests, they are crushed to make high-protein meal for livestock, and the heavily subsidized industry has found ingenious ways of moving its product in the form of "soy isoflavones," "textured vegetable protein," "soy protein isolate," and the other novel ingredients lurking on the labels of processed foods.
Twenty percent of Americans' calories now come from soybeans; the average person eats 25 pounds of the stuff a year. Just four seed oils — soybean, corn, cottonseed, and canola oil — account for 96 percent of the vegetable oil eaten in America today.
The spread of the seed-oil-rich Western diet around the world has been tracked by a statistical rise in the so-called diseases of civilization: asthma and arthritis, depression and Alzheimer's, heart disease and cancer, as well as metabolic disorders such as diabetes and obesity.