Dear Cecil: For years I've tolerated my friend's need for a strict vegan diet. I am lectured nearly daily about the benefits of veganism and the injustice of my murderous, meat-craving lifestyle. It's gotten to the point that we can't go out anywhere decent because there are few places vegan-friendly enough to suit his tastes. He has many redeeming qualities, so our friendship remains strong despite our philosophical differences. However, if there were an issue that would be a deal breaker, it would be his terrible, terrible gas. Its pure, unmitigated evil is indescribable. I'm pretty sure that in a highly concentrated form it could change laws of physics. Just god-awful. To make a dumb question long, are the rumors about vegan body odor, and specifically vegan gas, really true? Or is my friend just a naturally awful-smelling individual? Scott, via e-mail

Cecil replies:

Notwithstanding your assurances about redeeming qualities, Scott, I have to wonder what’s keeping this relationship going. It can’t be your friend’s pleasant personality, since he continually hectors you and accuses you of sordid crimes. It isn’t his scintillating conversation, unless lectures on your murderous meat-craving lifestyle are your idea of diverting chat. It’s obviously not his attractive physical presence. So what are you getting out of this — stock tips? Weekly payments? Does he give great head?

Call me a wuss, but I didn’t feel the question of intestinal gas was one I could profitably broach with the Vegan Society. Instead, as so often, I went browsing on the Internet. Googling vegan flatulence turned up 2,600 hits — considerably fewer than trepanation (skull boring), which netted an alarming 31,200, up from 6,120 just two years ago (and what’s that all about?). But it was more than enough to make you think twice about signing up for any long road trips with a bean zealot.

Suffice it to say that flatulence is a common complaint among and about vegans, and for that matter vegetarians generally. (For those of you who don’t know many vegetarians, they come in various flavors; vegans are the most hard-core, eschewing not only meat but animal products of any kind, including milk and eggs.) The problem is the body’s inability to fully digest the complex carbohydrates so abundant in the vegetarian diet and the consequent excessive production of gases such as hydrogen, carbon dioxide, and methane.

Vegetarian nutritionists claim this phenomenon abates once the intestinal flora adapt to the new menu; perhaps your friend is an intransigent case. However, I suspect high gas production is inherent in any diet consisting predominantly of plant products. Cows and sheep, for example, are marvelously adapted to all-veggie fare, yet they generate such prodigious quantities of methane-laden flatulence that some authorities regard them as major contributors to the greenhouse effect and thus to global warming. Some vegetarians have seized on this as further evidence of the wickedness of animal husbandry, to which skeptics mindful of people like your friend reply: Oh, sure, let’s quit having the ruminants pass gas all day in distant fields so we can do it ourselves at close range.

A matter avoided studiously in most discussions of this subject, and to which I now must delicately turn, is odor. While it seems inarguable that a vegetarian diet eventuates in increased flatulence, the gases produced in greatest volume — the aforementioned hydrogen, carbon dioxide, and methane — are odorless. The noxious fragrance of which you complain is produced by minute amounts of other digestive by-products, typically containing sulfur, such as hydrogen sulfide, methanethiol, and dimethyl sulfide.

Whether a vegetarian diet is uniquely productive of such irritants is the subject of hot debate. Some vegetarians claim that if anything they and their kind are more, not less, sweet-smelling than the meat-eating majority, and what’s more that they taste better. (And you thought my comment above about the various flavors of vegetarian was only a figure of speech.) I pass no judgments, observing only that foul smells are likely to be associated with particular high-sulfur foods rather than with a vegetarian diet in general. I have it on solid authority, for instance, that if you pack in the garlic you will stink like a son of a bitch. Broccoli and cauliflower are also notable in this regard. Willpower and muscle control won’t save you — if you don’t shed the noisome molecules in the form of flatus, they’ll be absorbed into your bloodstream and later waft from your breath or pores.

Some will say animal protein delivers far more sulfurous compounds than any plant protein, and that with modest care a vegetarian can minimize offense. Maybe so, but your friend doesn’t sound as though he frets about the opinions of others. Assuming you continue to truck with this character, can’t you socialize by phone?

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.