I’m 65 years of age. I have been taking acid reflux medication daily for at least 15 years and recently my doctor said my kidneys were declining. I’ve read that acid reflux medications taken over a long period of time, can cause kidney damage. By taking a probiotic, will it help reduce stomach acid, where I may be able to stop taking my acid reflux medication altogether?
The right resident strains - quite a few probiotics on the market contain things like active yeasts or soil based organisms. While these ingredients may be helpful to some, if you want to optimize your gut health, you need to look for strains that are resident to the human gut like those from the Lactobacillus, Bifidobacterium, and Streptococcus families.
Jotham Suez, Niv Zmora, Gili Zilberman-Schapira, Uria Mor, Mally Dori-Bachash, Stavros Bashiardes, Maya Zur, Dana Regev-Lehavi, Rotem Ben-Zeev Brik, Sara Federici, Max Horn, Yotam Cohen, Andreas E. Moor, David Zeevi, Tal Korem, Eran Kotler, Alon Harmelin, Shalev Itzkovitz, Nitsan Maharshak, Oren Shibolet, Meirav Pevsner-Fischer, Hagit Shapiro, Itai Sharon, Zamir Halpern, Eran Segal, Eran Elinav. "Post-Antibiotic Gut Mucosal Microbiome Reconstitution Is Impaired by Probiotics and Improved by Autologous FMT." Cell (First published: September 6, 2018)  DOI: 10.1016/j.cell.2018.08.047

Selecting a multi-strain probiotic is also consistent with the theory that filling your gut with enough good bacteria outcompetes any bad bacteria for the same space and resources. In your gut, the more diversified the good bacteria, the harder it is for the baddies to gain a foothold. With all this in mind, we only looked at supplements containing multiple strains of bacteria.
In the past, probiotics have been proposed as part of a weight loss diet. However, a 2015 meta-analysis looked at available randomized, controlled trials investigating this effect and determined that the studies did not seem to support this hypothesis, as body weight and BMI were not consistently reduced. The researchers did point out the need for better designed trials, because they were not convinced the results were based on well-designed science.
As with other types of supplements, scientists are still discovering the full potential of probiotics. However, when taken regularly, it is believed that they help support digestive health by helping maintain the balance of beneficial and non-beneficial bacteria in your digestive tract. Having a natural balance of good bacteria in the digestive tract can help defend against occasional digestive issues. In addition, probiotics play an important role in supporting immune health, since 70% of the body's immune system is found in the digestive tract.∗