Some protein bars contain sugar alcohols. You will be able to spot these on the ingredient list because they end in “-ol.” Examples of sugar alcohols found in some bars include maltitol, xylitol, and sorbitol. Sugar alcohols may cause gas, boating, or diarrhea in some individuals. Furthermore, many protein bars are not overly high in fiber. If you rely on these regularly instead of including high-fiber foods like fruits, vegetables, whole grains, nuts, and seeds, you may experience constipation.