Cereal and fungal beta-glucans taken orally are generally reported to be safe and well tolerated, and most research has not identified any major side effects associated with the use of beta-glucans.[1] Possible side effects are generally gastrointestinal, including diarrhea, constipation, nausea, flatulence, or abdominal cramping.[2]
Due to the immune-stimulating properties of fungal beta-glucans, use in people with an autoimmune disease should warrant caution. Although this hasn’t been explored in clinical research, it’s theoretically possible that fungal beta-glucans could worsen autoimmunity.
There’s a lack of research looking at whether beta-glucans are safe during pregnancy. It’s probably safe to assume that exposure to beta-glucans through food poses no harm.