I’ve occasionally seen the question asked “if methane from cows is so bad, well, what about the methane from the farting bean eaters?”. It might seem silly, but could replacing beef with beans actually lead to similar methane production simply by moving the methane from the cow’s gut to ours?
I thought it would be fun to run the numbers.
First up, beef. I found quite a bit variability in the numbers here, but I’ll use the paper “Is the Grass Always Greener? Comparing the Environmental Impact of Conventional, Natural and Grass-Fed Beef Production Systems” by Judith Capper. Based on her analysis, a pound of conventional beef corresponds to the emission of about half a liter of methane, from enteric fermentation and manure (aka burps and poo).
1 pound of beef (about 900 calories) ≈ 500ml of methane.
Next, legumes. This one was difficult because the data is fairly limited, but I found one paper. A 1971 study analyzed the farts of a handful of volunteers who had gas-catching bags attached to their “shaved buttocks” (fun stuff). After consuming 100 grams of white beans the average amount of methane produced and expelled via flatulence averaged 17ml over the course of 6 hours. 100 grams of white beans is a bit lower in calories than 1 pound of beef, so lets multiply by 2.7 to account for calorie differences. If we extrapolate up to get to 900 calories we come up with 0.046 liters of methane.
900 calories of white beans ≈ 46ml of methane.
Some other legume based foods resulted in far lower methane quantities in that study. Using the same framework tofu would clock around 5ml of gut derived methane.
It’s certainly possible that the numbers in both studies could be off, but even if the beef numbers ended up lower and the bean numbers were higher it still seems unlikely that they would end up even.
The Hammer of Health 