More than a third of Americans think that going gluten-free will help them slim down, according to our survey. But there's no evidence that doing so is a good weight-loss strategy; in fact, the opposite is often true. In a review of studies on nutrition and celiac disease published in the Journal of Medicinal Food, researchers said that a gluten-free diet "seems to increase the risk of overweight or obesity." The authors attributed that to the tendency for gluten-free foods to have more calories, sugars, and fat than their regular counterparts.

People who have celiac disease often gain weight when they go gluten-free, Fasano notes. That's because the damage gluten does to their small intestine prevents them from digesting food properly. Their digestive system heals after they have given up gluten and they're able to absorb key vitamins and nutrients from the foods they eat, including calories. In a study of 369 people with celiac disease, 42 percent of those who were overweight or obese lost weight after almost three years on a gluten-free diet, but 27 percent of them gained weight. In another study, 82 percent of those who were overweight at the start of it gained weight.

What about those who say they got rid of their belly when they ditched the wheat? There's no evidence that it was due to cutting gluten. "If people lose weight on a gluten-free diet, it might be because they're cutting calories, eating less processed food or sweets, or cutting portions of starchy foods like pasta and bread," says Samantha Heller, R.D., senior clinical nutritionist at NYU Langone Medical Center. "Instead of a cookie, they're eating an apple. Instead of pasta, they're eating a high-fiber, gluten-free whole grain like quinoa. Eating more fiber helps satiety and may aid in weight loss."

For information on healthy ways to lose weight, read our diet plan buying guide.

Our research found that in every category except ready-to-eat cereal, the gluten-free versions were more expensive than their regular counterparts, about double the cost, and in some cases considerably more. For example, brownies made from the Duncan Hines regular mix cost about 8 cents per serving; Betty Crocker's gluten-free mix cost 28 cents per serving. The per-serving cost of Nabisco's Multigrain Wheat Thins is 31 cents; it's 57 cents for the company's gluten-free Sea Salt & Pepper Rice Thins. DiGiorno's Pizzeria Four Cheese frozen pizza is $1.38 per serving; Freschetta's Gluten Free Thin & Crispy Four Cheese frozen pizza is $2.50 per serving.

Why are foods without gluten more expensive? "One factor in the price dif�ferential may be attributed to the added costs incurred by the manufacturer to meet certification and labeling regulations," explains Andrea Levario, executive director of the American Celiac Disease Alliance, a nonprofit group.

If you're convinced that you have a problem with gluten, see a specialist to get a blood test to check for certain antibodies associated with celiac disease. You need to be eating gluten when the test is done to get a proper diagnosis, notes Peter Green, M.D., director of the Celiac Disease Center at Columbia University's medical school. If it's positive, then you should have an endoscopic biopsy of your small intestine to check for damage.

Your symptoms may also be a reaction to something other than gluten in your diet. "We commonly see patients who go on a gluten-free diet and feel better for a week or two," explains Joseph Murray, M.D., a gastroenterologist at the Mayo Clinic. "It may be the placebo effect or simply because they're eating less. For some, their symptoms come back, so they decide to drop another food group, and then a few weeks later, when they're still not feeling any better, they make an even more drastic change, like going completely vegan. By the time they enter my office, they're on a severely restricted diet and still have symptoms." The reason? It often turns out their condition wasn't celiac disease or even gluten sensitivity at all, but another condition, such as irritable bowel syndrome.

Some people may benefit from something called the low-FODMAPs diet. The acronym stands for fermentable oligo-di-monosaccharides and polyols. They're the carbohydrates fructose (found in fruit and honey); lactose (in dairy); fructans (in wheat, garlic, and onions); galactans (in legumes) and polyols (sugar-free sweeteners); and stone fruit like apricots, cherries, and nectarines. The diet is complicated, however, and you might need to work with a GI specialist or nutritionist to help you figure out which foods to eat.

A recent study in the European Journal of Clinical Nutrition looked at 158 food products labeled gluten-free over three years. It found that about 5 percent-including some that were certified gluten-free-didn't meet the FDA's limit of less than 20 parts per million of gluten. The products were tested before the FDA's rule went into effect last summer. Still, that standard doesn't stipulate that manufacturers must test their products before making a gluten-free claim. "Cross-contamination can occur," Levario explains. "Gluten-free products may be manufactured on the same equipment used for wheat or other gluten-containing products." That can also happen when wheat is grown next to other grains. For example, oats are often grown in or near fields where wheat has been grown. As a result, wheat finds its way into the oat harvest and contaminates its subsequent products.

There's no way to completely protect yourself, but you can call manufacturers. "They should be transparent about what tests they use to determine whether a product is gluten-free," says the study's author, Tricia Thompson, M.S., R.D., founder of Gluten Free Watchdog. "If they insist that it's proprietary information, that should set off an alarm."

Another concern is that some products, particularly chips and energy bars, that carry a no-gluten claim contain malt, malt extract, or malt syrup, which are usually made from barley. As the study notes, "some manufactures mistakenly believe that the only criterion for labeling a food gluten-free is that it tests less than 20 ppm gluten." The FDA also stipulates that the food can't contain an ingredient derived from a gluten grain that has not been processed to remove the gluten. For people with celiac disease, inaccurate claims can be damaging. As always, it's best to read the ingredients list.

If you must cut out gluten, be sure to do it the healthy way:

Get your grains. Whether you're on a gluten-free diet or not, eating a variety of grains is healthy, so don't cut out whole grains. Replace wheat with amaranth, corn, millet, quinoa, teff, and the occasional serving of rice.

Shop the grocery store perimeter. Stick with naturally gluten-free whole foods: fruit, vegetables, lean meat and poultry, fish, most dairy, legumes, some grains, and nuts.

Read the label! Minimize your intake of packaged foods made with refined rice or potato flours; choose those with no-gluten, non-rice whole grains instead. Whenever you buy processed foods, keep an eye on the sugar, fat, and sodium content of the product.