Why are whole plant foods so good for us? Much of the benefit may be mediated by our microbiome. There are all sorts of things threatening our good gut bugs, like the over-prescription of antibiotics. However, the only factor that has been empirically shown to be important is a diet low in microbiota-accessible carbohydrates––in other words, prebiotics like fiber and resistant starch, only found one place in abundance: whole plant foods. We went from high-MAC diets to Big Mac diets, and may be suffering the consequences.
Intake of dietary fiber, which is the main source of MACs in the diet, is negligibly low compared to how we evolved. Such a low-fiber diet provides insufficient food for our gut microbes, starving ourselves of all the wonderful things they produce for us. A low-fiber diet is a key driver of microbiome depletion, and this loss is implicated in the rampant increase of chronic diseases that now plague the modern world.
We evolved getting perhaps a hundred grams of fiber a day. Our gut bugs must have been in heaven. How do you get even close to that? A cup of fruit may only have about three grams, a cup of vegetables, five grams. Why so little? Because fruits and vegetables are like 80 to 90 percent water. One has to go to the drier plant foods to really scale it up––like beans, at 15 grams, or intact grains like barley, over 30 grams per cup. But many people are avoiding common grains these days, like wheat barley and rye, due to gluten. But there is a dark side of gluten-free diets.
Now, if you have a condition like celiac disease, then you absolutely have to avoid gluten, but if not, the downsides include the potential for nutritional deficiencies, like not getting enough fiber, and toxic compounds, for example, the accumulation of heavy metals in people on gluten-free diets. Those following a gluten-free diet had significantly increased blood mercury levels––more arsenic flowing through their systems. The arsenic is likely due to increased rice consumption, because rice is a major ingredient in gluten-free foods. But you can certainly choose other grains, like sorghum—that’s my favorite rice substitute. And the higher mercury may just be because people eating gluten-free diets were tending to eat more fish for some reason. But the reason that 10 out of 10 of those without celiac disease or a recognized gluten sensitivity following a gluten-free diet experienced a pro-inflammatory gastrointestinal environment is likely due to starving your microbial self, not getting enough prebiotics, not getting enough fiber because you’re avoiding grains like wheat; so, whatever diet you choose for whatever reason, make sure you’re getting enough fiber.