James Hamblin in The Atlantic:
Forgetting Fiber
Of all the “probiotics” on the market, one of the few with actual evidence that it serves our microbes well is plant fiber. Fiber is the carbohydrate that humans can’t digest, yet we’ve long known that people who eat high-fiber diets tend to be healthier. Among multiple studies with similar results, one with 40,000 subjects found that a high-fiber diet came with a 40-percent lower than average risk of heart disease. Fiber also seems to protect against metabolic syndrome. One of the mechanisms behind these benefits appears to be that fiber essentially feeds the microbes in our guts, encouraging diverse populations. Those microbes are implicated in a vast array of illnesses and wellbeing. A diet heavy on meat and dairy is necessarily lower on fiber. In that light, the idea of “Paleo-veganism” is an interesting one. Loosely defined, it could mean eating minimally processed, plant-heavy diets. If a flaw in veganism is that some people think they can drink juice and eat white bread all day and be healthy, that might be sustainable for the planet but not good for you. Paleo-veganism (again, loosely defined lest we descend into madness trying to discern the plant varieties this would include) might work as a rule of thumb that generally keeps us focused on the sorts of foods that promote health.
More here.