Denis Hayes has beef with the modern food system

Denis Hayes may be best known as an original organizer of Earth Day and the current president of the Bullitt Foundation, but he also has another pet environmental issue: Food, or more specifically, cows.

"Other than human beings, cows did more than anything else to shape the contemporary United States," Hayes said during a talk at the VERGE 2015 event in San Jose, California, late last year shortly after the release of his recent book, "Cowed."

From blazing the trail for settlers heading for the frontier to clearing forests for early development to ultimately becoming meals synonymous with Americana — burgers, steaks — Hayes argued that cows have an even bigger impact on the modern economy.

"When we think of cows as part of the economy, we often think of meat, milk and leather, but it actually goes on to a great many other products cows are a part of," Hayes said, flashing up a slide calling out things such as collagen injections, wallpaper paste and surgical sutures.

Still, as environmentalists and nutritionists increasingly emphasize, all that comes with a cost. Livestock accounts for about 14.5 percent of global greenhouse gas emissions, and cattle accounts for 65 percent of that figure. Red meat is also linked to higher risk of heart disease and some cancers, not to mention ailments such as antibiotic-resistant disease that stem from industrialized farming's reliance on animal antibiotics.

"Four times as much antibiotics now go into livestock as humans," Hayes said, citing 23,000 deaths from antibiotic-resistant disease in 2014 alone.

While emphasizing the power of the Big Food lobby, Hayes urged consumers to limit beef intake to a half-pound per week and shop for grass-finished, USDA certified organic, antibiotic-free and certified humanely raised beef.

"Be just like you are with wine," he said. "Be selective."