[joblai (OP)]

Due to the amount of pulses and fibre in their diet, are vegans more flatulent and emit more methane?

[Bored chemist]

Probably not. And, to be sensible about it, you would need to account for the methane produced by the farm animals the non-vegans eat

[chris]

According to my friend Giles Yeo, who appears on our show from time to time and recently agreed to go vegan for a BBC documentary, he did get very "windy" (his words); however, this did settle down with time, so the interpretation is that the transition in intake from meat-based diet to vegan diet applies different selection pressures to the microbiome, which initially rebels in a flatulent way...

Here's a reference: https://www.thenakedscientists.com/articles/questions/why-does-food-make-me-happy

Also, we did have a similar discussion about this topic previously, here: https://www.thenakedscientists.com/forum/index.php?topic=75298.0

[AnnaScott]

It is well known that grassy food wanders in the stomach, when we eat a lot of fiber, we often fart. But poorly digestible meat products rot more, decompose for a long time, and therefore less gas is released during splitting.

[evan_au]

poorly digestible meat products rot more

More than what? Fiber?

Digestible foods (whether animal or vegetable) are broken down into small molecules which can be absorbed into the gut. If you call this "rotting", they both rot equally.

Indigestible foods (whether animal or vegetable) are not broken down into small molecules which can be absorbed into the gut, and so pass through the digestive system. If you call this "rotting", they both rot equally.

But since humans generally avoid eating bones, vegetables contain a greater percentage of indigestible matter than meat.

grassy food wanders in the stomach

Why? It's the same distance from top to bottom of the stomach (and from mouth to colon).

[Bored chemist]

It is well known that grassy food wanders in the stomach,

No.
That's just hokum.

[AnnaScott]

My nutritionist says that flatulence - bloating and increased flatulence in the intestines can be caused by the specifics of nutrition: poor grinding of food in the mouth, respectively, poor digestion in the stomach, food is delayed in the intestine, causing putrefactive processes, producing gases. In this case, the processes of splitting go wrong and far from the molecules, there remains a lot of non-digestible food. Insufficient chewing and swallowing too fast, especially meat. The emergence of flatulence contributes to the food products with high gas-generating potential: onions, celery, cabbage, radishes, onions, carrot cucumbers, potatoes, apples, peaches, plums, grapes, bananas, pears, apricots. Meat eaters do not fart less because they consume less fiber, bran products, vegetables and fruits.

[alancalverd]

Methane ain't the problem. Farm animals exhale CO2 while they are alive, and this accounts for about 25% of all anthropogenic emissions.

We probably fart less CH4 than the ruminants we eat, because we don't have the capacity for anerobic digestion of celluose.

[Bored chemist]

food is delayed in the intestine, causing putrefactive processes,

The acidic conditions in the stomach would prevent putrefaction.