Yes, a bean-laden vegan diet is likely to cause a larger volume of flatulence.
A 2011 study published in BMC Nutrition concluded that incorporating beans (an important staple food for vegans) has the potential to increase flatulence, but for many people this effect may only be temporary.
First, perception of flatulence increase is variable by bean type and across individuals. Second, after a few weeks of daily bean consumption, people perceive that flatulence occurrence returns to normal levels. Third, a small percentage of individuals may be bothered by increased flatulence regardless of the length of time they consume legumes.
The mechanism by which flatulence is affected is well understood.
Most legumes contain relatively high amounts of both dietary fiber and resistant starches. The soluble oligosaccharides found in legumes are not digestible by human intestinal enzymes alone. Instead, oligosaccharides such as raffinose and stachyose are broken down by bacterial fermentation in the intestines. Although some rectal gas is due to the ingestion of air, the majority of flatulence is produced from bacterial fermentation. The byproducts of this degradation are hydrogen, carbon dioxide, methane, and sometimes sulfur, depending upon the bacteria. Normal intestinal processes move these gases out of the body in the form of flatus. Removal or alteration of the oligosaccharide content of legumes will reduce the amount of gas produced.
A 1966 study called Effects of various soybean products on flatulence in the adult man showed that soy protein and soy fat are not significantly associated with flatulence production. Another 1966 study called Effects of Bean Diets on Concentration of Carbon Dioxide in Flatus concluded:
A direct relation exists between the volume of flatus produced and the volume of beans consumed in amounts of 27 per cent or more of the diet. The principal gas accountable for the increased flatus volume is carbon dioxide.
Beans can (and are) processed in various ways to reduce the amount of flatus produced.
- Fermenting soybeans to produce natto and tempeh greatly reduces oligosaccharides.
- Tofu has most (but not all) of the oligosaccharides removed, so that it causes less gas than eating an equivalent number of soybeans directly.
In conclusion, yes a vegan diet is very probably associated with a higher volume of flatulence due to the increased inclusion of beans, although results are likely to vary between individuals and even over time for a particular individual.