The Food and Agriculture Organization of the United Nations has predicted that our meat consumption will increase by as much as 15% by 2050. Which is bad news: some figures estimate that animal agriculture is responsible for half of global greenhouse gases. With that big of a role in the causes for global warming, cutting back on eating meat has got to make an impact. And according to a study from Oxford University, it will: if everyone in the world followed World Health Organization (WHO) guidelines for meat consumption, we could cut greenhouse gas emissions by 29% by 2050. What's more, 5.1 million lives could be saved by reducing illnesses like heart disease and cancer, and $21 trillion could be saved in healthcare and other related costs. Those guidelines call for a maximum of 10.5 ounces (300 grams) of red meat per week -- that's about three Big Macs -- which is about half what the average American ate in 2012.