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The die-off within us: Are our low-fiber diets ruining our descendants’ lives?

gut_bust_portraitMembers of the Hadza, a 300-person remnant of an all-but-vanished Tanzanian hunter-gatherer society, consume 150 grams of fiber per day on average. That's a clump of indigestible material approximately the weight of a decent-sized hamburger -- and it's ten times the daily amount the typical burger-bingeing denizen of the industrialized world ingests.

A daily five-ounce fiber feast keeps the trillions of one-celled creatures (mostly bacteria) that live inside our guts abundant and productive, which was probably essential to keeping our ancestors healthy during the first 95 percent of our species' evolutionary history when we were all hunter-gatherers.

Forget low-fat. Forget low-calorie. Are you getting enough fiber in your diet? Nowhere near enough, no doubt, and this could be setting back not only your own health but that of your descendants -- maybe irreversibly.

Fiber is a term designating complex carbohydrates that we can't digest but our gut-resident microbes can. In fact, they can't live without it.

In "Gut Bust," my recently published Stanford Medicine article about a vanishing society within us, I wrote:

[H]hundreds, even thousands, of distinct bacterial species inhabit every healthy individual’s large intestine. Far from being parasitic, this community of microbes, mainly bacteria, gets along with us so well it might be viewed as an additional organ. If your heart or your lungs or your liver or your pancreas were losing substantial amounts of cells, wouldn’t you be concerned?

This is what seems to be happening to the gut communities of people in industrialized societies, and it's unlikely to be good. A growing list of health disorders endemic in industrialized societies, from obesity to autism to cancer and cardiovascular disease, may be linked to the health of the complex microbial ecosystems that reside in our gut.

In the article I describe recent work by Stanford microbiologist/nutritional researchers Justin Sonnenburg, PhD, and Erica Sonnenburg, PhD, suggesting that a pervasive lack of fiber in today's typical diet may be to blame. Moreover, their studies suggest, the depleted state of our "microbial organ" could be heritable and, perhaps soon, irreversible:

[T]his ongoing mass extinction in our guts could be passed along to future generations... If that suggestion turns out to be true, then once an entire population has experienced the loss of key bacterial species, simply “eating right” may no longer be enough to restore these lost species to the guts of individuals in that population. Those who live in advanced industrial societies may already be heading down that path.

If it makes you feel better, the Hadza diet also includes goodly amounts of meat when it can be caught and honey when it's in season, and the hunter-gatherers say they'd munch fiber-free meat and honey all the time if only they could, just like us. Except that they can't, and we can. So we do.

It would surely be better for us if we didn't. But with wall-to-wall fast-food commercials, box after box of fiber-free, breezy-prep processed foods lining the shelves of 24/7 supermarkets, and the sheer pleasure of biting into a burger made of the Real Thing -- meat! -- it ain't easy.

So the Sonnenburgs (they're married) have written a book for non-scientists -- The Good Gut -- which explains the importance of our intestinal microbiota and offers practical tips on how to turn the tide, up our fiber intake and keep our gut bugs happy and our bodies healthy.

Previously: Ties that heal: Stanford Medicine magazine examines relationshipsCan low-fiber diets' damage to our gut-microbial ecosystems get passed down over generations?,  Getting to the good gut: How to go about it, Civilization and its dietary (dis)contents: Do modern diets starve our gut-microbial community? and The future of probiotics
Photo of Justin and Erica and their children by Timothy Archibald

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