The question we asked Google was simple enough: What are the most popular diet searches in every metropolitan region across America?

What we got back showed a startling trend: the slow spread of the gluten-free diet across the United States.

2006

Here you see Google searches about diet in 2006. The organic food movement seems to be a key area of interest in many areas, and Americans also search for information about vegan eating, the low-carb diet, the South Beach Diet, and Atkins. You'll notice only a couple of regions are interested in the gluten-free way.

2009

By 2009, the gluten-free diet begins to go viral. As Alan Levinovitz, author of the The Gluten Lie, told me, "It was slow and steady progress. [Alternative medicine proponent] Joe Mercola started talking about evils of gluten pretty early on. Jenny McCarthy started talking about it in the early 2000s. The book Dangerous Grains came out in 2002."

In the late 2000s, Elizabeth Hasselbeck of the View started talking about gluten-free on The View, and her book, the G-Free Diet, came out in May of 2009. "That's a huge candidate for explaining the 2009 spike," Levinovitz added. Then came Wheat Belly and Grain Brain — two best-selling books that promoted the gluten-free way for better health and weight loss.

2011

By 2011, an interest in gluten-free has nearly conquered America. According to Fast Company, retail sales of gluten-free products grew at a rate of 34 percent between 2009 and 2014. By 2016, Americans are expected to spend more than $15 billion on gluten-free products.

2015

You can see gluten-free continues to dominate Google searches even today.

Of course, there are good reasons some people follow a gluten-free diet. Celiac disease is a serious, diagnosable autoimmune condition that causes people's immune systems to act up whenever they eat gluten. (About 1 percent of Americans have celiac disease.)

But many more people are surely searching for the diet in order to lose weight. And there's actually no good evidence that gluten-free eating helps.

In a 2006 study that tracked 371 gluten-free dieters, 82 percent actually gained weight after two years. Another study followed 149 kids with celiac disease who went on a gluten-free diet for at least 12 months; in this case, the percentage of overweight children nearly doubled.

This weight gain may, in part, be attributable to people swapping regular pastas and breads for gluten-free versions and thinking them healthier and perhaps eating more. But gluten-free alternatives are sometimes simply less healthy than the regular versions. As an article by Linda Geddes in New Scientist noted: "A team in Spain recently examined the daily diets of 58 people with celiac disease and found that, in general, they contained more fat and less fibre than those of people who do eat gluten."

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