I'm assuming they do like brussel sprouts and other gassy veggies...they do with people, so I'm assuming it could happen with rabbits. I just don't take the chance, I do know they give my one bun soft stools if he gets too much...I've never heard that bananas can cause gas. Never seen it happen. They are high in sugar though and so only a small amount should be given. Any sudden large amounts of sugar - from any source - can cause a tummy upset.