ROBERT SIEGEL, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

In the last few years, wheat has gotten a bad rap. Eating gluten-free has become a kind of cure-all for what ails you. It can help you lose weight, reduce bloating, eliminate headaches. And while it's not clear that wheat really is linked to so many ailments, there are a lot of theories out there about why gluten intolerance could be on the rise.

NPR's Allison Aubrey reports.

ALLISON AUBREY, BYLINE: A decade ago, if you heard about someone taking wheat out of their diet, chances are it was a person with celiac disease. About one percent of Americans cannot tolerate the gluten protein in wheat; it makes them very sick. But nowadays, lots and lots of folks are experimenting with wheat free diets. And a lot of the interest is driven by a best-selling book called "Wheat Belly." William Davis is the author.

WILLIAM DAVIS: Wheat is the most destructive thing you could put on your plate, no question whatsoever.

AUBREY: Wow, that's a strong statement given our long history of bread, pasta and pizza lovers. But Davis, who is also a physician - a practicing cardiologist - became passionate about this topic when he took wheat out of his own diet. He believes that this made him much healthier.

DAVIS: So, I was diabetic about 25 years ago. I'm no longer diabetic and I had like mind fog and mood swings, and joint pains and acid reflux. I had all that sort of stuff.

AUBREY: And he says what he's seen with his patients who go wheat free is similar.

DAVIS: You take wheat out of the diet and you literally see lives transformed.

AUBREY: Now, Davis' beliefs are way outside the mainstream. Most doctors don't think that wheat causes problems for most people. Nonetheless, with a growing number of people claiming they feel better without wheat, Davis says there's something going on here. And his theory is that it's modern varieties of wheat. He says the wheat of yesteryear did not make people sick.

DAVIS: We know that celiac disease has doubled in the last 20 years. Now, humans have probably had not changed, so it's more likely culprit is the wheat itself that has changed.

AUBREY: Now, it is true that about 40 years ago, wheat breeders introduced new varieties of wheat that helped farmers increase their yields per acre. But this claim that these changes are somehow making people sick doesn't sound right to scientists who work with wheat.

DONALD KASARDA: I never thought that wheat was toxic.

AUBREY: That's Donald Kasarda. He has studied gluten proteins for more than 40 years as a USDA research chemist. He says when he came across the idea that the rise in celiac and gluten sensitivities was linked to breeders increasing the amount of gluten in wheat, he was very skeptical.

KASARDA: That seemed strange to me.

AUBREY: As far as he knew, gluten levels had remained about the same. And when he dug deeper, combing through the scientific literature and comparing the gluten levels in wheat from the early part of the 20th century compared to the latter half, he found gluten levels had not changed much.

KASARDA: As I suspected, I didn't find any evidence that this is true.

AUBREY: And he's published his findings in the peer-reviewed Journal of Agricultural and Food Chemistry.

Now, "Wheat Belly" author William Davis believes there are more subtle changes to wheat that are causing the problems. But there's no scientific agreement on this point. And meanwhile, in the medical community, there's a lot of pushback against the idea that wheat has become toxic to all of us.

DR. DANIEL LEFFLER: I certainly think that's an overstatement.

AUBREY: That's physician Daniel Leffler, a leading celiac expert. He directs research at Beth Israel Deaconess Medical Center and is on the faculty at Harvard Medical School.

LEFFLER: I don't think there's one evil food that's causing all the problems in our society.

AUBREY: In fact, he says most people eat wheat with no problem.

LEFFLER: There is good evidence that the vast majority of people actually do just fine with wheat.

AUBREY: But Leffler says it is true that the prevalence of celiac disease is going up to nearly one percent of the population. And that some portion of the population does have a gluten sensitivity. But he says there's almost certainly not one single cause, like a change in wheat breeding.

LEFFLER: We sort of chafe at these over-simplistic theories that purport to explain an entire rise in a disease.

AUBREY: Leffler says the increase in celiac disease comes at a time when lots of other autoimmune diseases and allergies are on the rise, too. And what might explain this phenomenon is the so-called hygiene hypothesis. This is the idea that our environment has become so clean that our bodies no longer have to fend off so many bugs and infections. So our immune systems look for something else and they start to overreact to things that should be harmless, like wheat or peanuts.

LEFFLER: You can see quickly how this gets very, very complicated

AUBREY: And there are many other theories that could help explain gluten intolerances, everything from changes in gut bacteria, to antibiotic use early in life, to the timing of introducing babies to wheat and other grains. So Leffler says stay tuned on this one and don't think you have to avoid wheat if you're a person who enjoys breads and pastas and tolerates them well.

Allison Aubrey, NPR News.

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