You can't swing a dead cat without hitting an article about the microbiome on the internet. Changes in the zillions of bacteria that reside in our bowels now get the blame and the glory for a variety of conditions. Collecting poo and analyzing the actual contents over time to look at contribution to disease development would take years and be cumbersome. Interested investigators therefore think of proxies that may influence microbiota that can be studied with less fuss.
A group from Buffalo, New York, decided to examine the intake of beneficial bacteria and markers of kidney dysfunction. Some people take capsules of these good bacteria, known as probiotics, while others get these critters from yogurt that still contains the active cultures responsible for its conversion from milk. They used the data from the US National Health and Nutrition Survey (NHANES) to compare yogurt and probiotic use with markers of kidney disease, including microalbuminuria and level of estimated glomerular filtration rate (eGFR). Yogurt consumption was self-reported by participants as frequent (eaten 3 or more times weekly) or infrequent (less than 3 times weekly). Probiotic use was extracted from the study surveys.
From 1999-2012, NHANES included 41,243 adult subjects with complete covariate data available for 32,749 in the cohort with probiotic data (1999-2012). Data on yogurt consumption was limited to 6853 subjects (2003-2006). Yogurt and probiotic use was associated with higher socioeconomic level, more females, and fewer African Americans. Yogurt and probiotic consumers also had fewer comorbid conditions. These differences were adjusted prior to multivariate analysis, since all of the conditions associated with frequent yogurt and probiotic intake reduce the risk of kidney problems. Frequent yogurt and probiotic users showed lower risk of either reduced eGFR or microalbuminuria (OR = 0.76; 95% CI = 0.61 - 0.94). When these markers of kidney problems were examined separately, yogurt and probiotic consumers still had lower risk of albuminuria (OR 0.74; 95% CI = 0.57 - 0.95), while no significant change in the risk of low eGFR could be demonstrated.
This study has a boatload of limitations, including relatively small sample size and its cross-sectional nature. While they adjusted their analysis for confounding variables known to change kidney disease risk, it is still likely that yogurt and probiotic consumption is a marker of "healthier people" at lower risk. While they speculate about effects of probiotics and yogurt on the microbiome, they have no evidence of this effect in their population.
For most folks, eating a few yogurts will cause no harm. It might be beneficial. But this study provides no firm foundation for a recommendation.
Nutrition Journal (2016) 15:10 * DOI 10.1186/s12937-016-0127-3