“Gluten-free diets decrease levels of good gut bacteria and increase levels of bad gut bacteria.”A while back, this study made the rounds. Anyone who wanted to ridicule people on elective gluten-free diets could now do it with a study under their belt. Never mind the fact that they rarely actually read the full study. Never mind the fact that they didn’t understand the significance of a shift in gut microbiota composition. They just knew that it was “bad”, that it was proof we gluten-abstainers were foolish and wrong. But the actual study paints a slightly different picture. Actually, a phrase embedded in the quote in the abstract says it all. Healthy gut bacteria decreased and unhealthy bacteria increased parallel to reductions in the intake of polysaccharides after following the GFD.
The gluten-free diet wasn’t hard on the subjects’ gut bacteria because gluten was absent. It was hard on their guts because it was poor in fermentable substrate for the gut bacteria to consume. They replaced whole wheat based foods with refined grains and starches that happened to be gluten-free. Whole wheat is a decent source of prebiotic fiber, if nothing else, and that fiber feeds the bacteria. Rice flour, (cooked) potato flour and starch, tapioca flour, corn meal, and most other gluten-free flours or starches used in gluten-free packaged foods are poor sources of prebiotic fiber. Starved of food, the beneficial gut bacteria get crowded out by the pathogenic bacteria.
If you look at the PDF detailing the RS content of various foods, you’ll see that grains are the top source of resistant starch in the diets of most industrialized nations. They’re not incredible sources, they’re not dense sources, but they’re all most people have. Your average American isn’t making green banana smoothies, eating cooked and cooled potatoes, and stirring raw potato starch into sparkling water. They’re chowing down on wheat and other cereal grains.
Takeaway: If you’re going gluten-free, you have to replace the fermentable fiber in whole grains with the fermentable fibers and resistant starches in fruits, vegetables, green bananas/plantains, cooked and cooled potatoes, and raw potato starch. This will surpass and improve upon the modest amounts of said fibers/resistant starches found in wheat and other gluten grains. Most of you already know this (the subject has received a lot of attention on this blog for years), but it’s important to pass this on to others who may not.