Dear Dr. Roach: In a recent column, you OK’d stevia, which I had heard could negatively impact our microbiomes. I am borderline prediabetic, and I had stopped using stevia accordingly. However, I hate unsweetened coffee. Can you comment on stevia’s impact on our microbiomes in your column? — M.M.

Answer: I wish I could give you an answer that everyone would agree with, but the literature is conflicting. I found a well-done trial from 2024 showing that there were no significant changes in the microbiome (a term for the whole complex array of bacteria and other tiny life forms in our intestines) among volunteers taking five drops of stevia twice daily for 12 weeks.

Another study (from before the trial) showed increased diversity in a laboratory model, which is generally a good thing. Finally, a 2022 analysis of all trials found no evidence of harm to the microbiome. Based on this, I think it unlikely that stevia has a serious adverse effect on the microbiome.

Multiple studies have found that sugar has adverse effects on the microbiome, so if your main concerns are diabetes and your microbiome, the evidence at the present time supports stevia rather than sugar in your coffee.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Drive, Orlando, FL 32803.