Cassandra Boyd with garlic and onion (IMAGE) American Society for Nutrition Caption Researcher Cassandra Boyd holding garlic and onion, two foods that the study revealed to be dense in prebiotics. Credit Cassandra Boyd Usage Restrictions Credit must be given to the creator. License CC BY Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.