Just Eat More Fiber

January 11, 2018

Diets can be overwhelming, but one small change can do a lot.

In the spirit of Drynuary, I’d like to propose another health-oriented month of the year. Perhaps called Crunch-uary or Poop-tober, it would be 30 days in which Americans, for once, eat enough dietary fiber.

Currently, Americans only eat about 16 grams of fiber —the parts of plants that can’t be digested—per day. That’s way less than the 25 to 30 grams that’s recommended.

There are so many reasons why, from fast-food marketing to agriculture subsidies, but one contributing factor is the slow death of cooking, and the rise of the restaurant meal. Americans now spend more on food at restaurants than they do at grocery stores, but restaurant food tends to have even less fiber than the food we would otherwise eat at home.

One problem seems to be that restaurant meals aren’t typically loaded with two of the best sources of fiber, unprocessed fruits and vegetables. A revealing study from 2007, in which researchers interviewed 41 restaurant executives, showed that restaurants think fruits and vegetables are too expensive to feature prominently on the menu, and “61 percent said profits drive menu selections.” They also opposed labeling certain menu items as healthier choices, saying that would be “the kiss of death.”

So people like to eat out, and when they do, they prefer mushy, fiber-free comfort foods. But that’s a pretty dangerous road to go down.

As my colleague Ed Yong has written, low-fiber diets make gut bacteria more homogenous, possibly for generations. Mice that are fed high-fiber diets have less-severe food allergies, potentially because gut bacteria break down fiber into short-chain fatty acids, which support the immune system.

A more recent study in mice found that a low-fiber diet can spark inflammation in the intestines. We still need more studies to understand exactly how fiber and the microbiome interact in humans. But we do know that hunter-gatherer communities in Tanzania and elsewhere, who don’t eat Western diets, eat about 100 grams of fiber a day and have much more diverse microbiomes than Westerners.

“We’re beginning to realize that people who eat more dietary fiber are actually feeding their gut microbiome,” Justin Sonnenburg, a microbiologist at Stanford University, explained to NPR.

There are also already plenty of other studies detailing the many ways fiber boosts health.

Behold, an extremely confusing flow chart, from a 2005 study, showing how fiber leads to greater satiety, less insulin secretion, and more short-chain fatty acids, which all amounts to one thing: Less body weight.

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