Which type of bean causes the least amount of flatulence without soaking?

Perceptions of flatulence from bean consumption among adults in 3 feeding studies states

It is important to recognize there is individual variation in response to different bean types.

A review in MedMD on beans states All Beans Aren't the Same in Gassy Side Effects

So any answer to your question is likely to be subjective. Also, when comparing beans to lentils it is probably worth to consider that lentils are often cooked un-soaked, but beans are frequently pre-soaked and/or require (much) longer cooking times than lentils. So flatulence comparison will be influenced by cook time as well as food type. From personal experience, cooking any beans with kelp might assist digestion.

The short answer is

• Phaseolus coccineus
• Flat bean
• Pea
• Snow pea
• Black-eyed pea
• Phaseolus vulgaris
• Vicia faba
• Lathyrus clymenum
• Lentil

Flatulence depends on many factors

1. on the bean-side, like:
   • presence of toxins (try ecologically grown types)
   • presence of salt in the prepared food (try to lower)
   • soaking time and the acid-base balance of soaking liquid (can be improved with Sodium bicarbonate)
2. from the consumer side:
   • eat beans regularly to get used to your organization
   • chew thoroughly to increase the digestive surface to have less strain on stomachs.
   • varies by Dosha and blood type

Lentils cause less flatulence and they don't need soaking. Try the small ones first (red lentils, beluga lentils...)