The Strand Similar to multivitamins, not all probiotics are created equal. Different probioitcs have different bacteria strains with varying benefits; and some probiotics may contain more than one strain, so it’s important to do your research. Some strains may help with gastrointestinal issues like diarrhea, while others may not have any effect on the GI tract at all, according to Keri Gans, RDN, author of The Small Change Diet. If you’ve made the decision to take a probiotic supplement but you’re unsure about which strain to take, ask your doctor or a registered dietitian for a recommendation. “You most likely will not have any negative side effects from using the wrong strain, but you may also not see any benefits,” says Gans.