I never could finish Upton Sinclair's The Jungle about America's 20th Century meatpacking industry -- it was too depressing. But I did drive through Colorado last summer and witnessed loads of cattle standing in mud and excrement off the interstate between Ft. Morgan and Estes Park. The horrid conditions and nauseating, inhumane stench were shocking -- made me wonder where our burgers and steaks really come from.

AOL Health's Where Fast Food Comes From summarizes a new study which analyzed the carbon and nitrogen isotopes in meat served at Wendy's, McDonalds and Burger Kings across the nation, to determine the animals' diets and conditions raised.

Study authors claim test results reveal cattle were strictly confined and fed predominately corn. Burger King meat did offer the greatest variability -- some cattle may have grazed on natural vegetation and/or fed other feeds instead. Chicken samples revealed extreme confinement, and the isotope signatures of some meat indicated animals had consumed their own waste. Yuck.

The study has its critics, one suggesting nitrogen-enriched feed could explain the results, not necessarily extreme confinement. Interestingly, while McDonalds and Wendys did not disclose how their food is produced, in 2007, Burger King committed to two percent cage-free eggs and 10 percent of its pork sourced from sows able to move in pens versus confined in crates. I usually order fast food salads -- they're looking even better right now.