How is the digestive process of vegans influenced by their eating patterns? Are there any differences - for example - in gut microbiota?
There is lots of evidence suggesting that eating animal products, or avoiding them, has a strong influence on gut bacteria. A study discussed in this article, for example, found that switching to a diet of only animal products changed the composition of gut bacteria communities in a single day.
This study in the European Journal of Clinical Nutrition found (examining stool samples - so the literal answer to your question is "yes") that vegans were more likely to have a slightly acidic gut environment due to higher levels of short-chain-fatty-acids. This meant that healthier bacteria were likely to thrive, while pathogenic ones (e.coli and enterobacteriacea) were not, and were found in lower numbers, suggesting an overall protective effect on health. Results for vegetarians were between those for vegans and omnivores. Researchers suggested the results appear to be due to the higher levels of starchy carbohydrates and fibre in vegan diets.
Maintaining a strict vegan or vegetarian diet results in a significant shift in the microbiota while total cell numbers remain unaltered.