As if nutrition advice isn’t confusing enough, there’s a new dietary trend that focuses more on the health of our planet than on the health of our bodies.

Called “sustainable nutrition,” it’s the idea that our food choices can impact the environment.

Maybe you’ve heard claims that you can reverse climate change by eating less meat. Environmental and animal rights activists blame cattle emissions — or to put it bluntly, cow farts — for climate change. That’s because cows emit methane, a greenhouse gas...