Here is some info on feeding peas. It was posted by BettaBaby, who is/was a member of FishForum and she is an aquatics specialist/nutritionist.
"With all that said, I also have to mention one more thing before I go. The deal with constipation has arisen again, as I read a suggestion to feed your betta peas to relieve it. Please don't do this! Bettas are carinvores, which means they eat meat. Their pellet foods are made of primarily meaty ingredients to ensure they have good nutrition. The digestive tract of a betta is not designed to handle heavy vegetable matter, such as peas. While the fish may eat the peas, that does not make it good for him. Babies eat candy, that doesn't make it healthy. I don't know who started the whole idea of feeding a betta peas to relieve constipation, but I strongly warn everyone against it. Peas act as a laxative. Imagine making castor oil a regular part of your child's diet... or running for it everytime your child fails to poop on schedule. All that does is mess up the stomach and digestive tract, and the end result is an early and very painful death in the fish."