You have seen lots of claims about probiotics - Activia and that stuff the sportscaster sells. You can save your money. Anything you are consuming with that kind of impact could just as easily be doing as much harm as good, but your yogurt is not making a difference, it is just a delicious placebo.

The microbiome is a system so turning one knob isn't doing anything meaningful but it's among the latest miracle health fads. A study in the Journal of Agricultural and Food Chemistry even says the benefits of good bacteria outweight the negatives of much-maligned white bread.

Isn't white bread still bad? Unless the topic is Yogic Flying, you could live a completely healthy life ignoring all nutritionists, unless they say something obvious like 'eat a balanced diet'. Vegetarian fads, sugar-free, gluten-free, no carbs, no wheat, there is no evidence that they help anyone without a debilitating condition related to a specific food (like gluten with celiac patients).  

Sonia González and colleagues say that when certain populations of bacteria drop, people become more prone to disease, which is true, and they note that one of the most effective ways to maintain a good balance of the microbes living in our guts is through our diets. Also true. Rather than focus on individual fibers and probiotics, they instead focused on the role of polyphenols, which are common in much of what we consume — spices, teas, fruits and vegetables — and how those might help balance our gut microbes. 

In a small pilot study, so don't start wolfing down white bread, they asked 38 healthy adults questions about their diets and figured out which bacteria were present in the participants' stool samples. Their analysis revealed that pectin, a compound in citrus fruits, lowers the levels of some helpful bacteria.

This is contrary to previous research on pectin alone. The researchers suggest that pectin interacts with other substances in oranges, leading to this unexpected effect.

Their most novel finding, they said, was that white bread boosted Lactobacillus, a group of beneficial bacteria.