“We’re going to reveal the major signs of gluten sensitivity,” promised Dr. Oz on one of his shows several years ago. His first sign: weight gain.

“It’s not just eating the gluten that makes us heavy,” Dr. Oz claimed. “When you have a gluten sensitivity, it’s really getting your hormones out of whack, and that then leads to inflammation and swelling.”

This makes you “hold on to fat” that you should have burned off, he told his viewers. “And even if you go on a diet, if there’s gluten in there, you don’t lose weight.”

Does celiac disease lead to weight gain?

Weight gain is anything but typical in celiac disease, the classic, well-studied illness caused by an autoimmune reaction to gluten.

“Do people gain weight because they have celiac disease that’s not diagnosed?” asks celiac disease expert Joseph Murray. “Not usually. Usually they tend to be underweight compared to the general population.” Murray is a gastroenterologist and professor of medicine at the Mayo Clinic in Minnesota.

That’s because their reaction to gluten damages their intestinal lining, so it absorbs less—not more—of the food they eat. “Some people with celiac disease don’t absorb as many calories from what they’re eating as a normal person would,” notes Murray.

What are the common symptoms of celiac disease?

“Diarrhea, bloating, gaseousness, abdominal pain, anemia, fatigue, joint pain, headache, skin rashes, and mouth ulcers,” says Murray, who is also president of the North American Society for the Study of Celiac Disease. “And in children, growth failure, short stature, and maybe developmental delay.”

Dr. Oz may have been talking about non-celiac gluten sensitivity. Some people have fewer GI symptoms like gas or diarrhea when they stop eating gluten, even though they don’t have celiac disease.

Is weight gain a major sign of non-celiac gluten sensitivity?

It’s hard to say, for one good reason: “We don’t know if there is a true non-celiac gluten sensitivity,” says Murray. “It could be wheat intolerance, it could be wheat sensitivity, or it could be something else entirely.”

In 2011, Australian researchers reported that 34 patients without celiac disease had fewer GI symptoms on a gluten-free diet. “That study was probably the best evidence that there may be a condition called non-celiac gluten sensitivity,” says Murray.

"That study was probably the best evidence for non-celiac gluten sensitivity," says Murray. "But the researchers corrected that with their second publication."

In 2013, the Australians put 37 patients with possible non-celiac gluten sensitivity on a diet that was low in FODMAPS (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols). FODMAPS include fructose, lactose, sorbitol, and other short-chain carbohydrates that are poorly absorbed. A low-FODMAP diet is also low in gluten, but it’s not gluten-free.

While their symptoms lessened when people ate the low-FODMAP diet, adding back gluten produced no more or fewer symptoms than adding back a placebo (whey).

“That tells us that their symptoms were probably not due to gluten,” says Murray.

“The whole premise that there is a disorder called non-celiac gluten sensitivity is way overblown. There really isn’t hard scientific evidence to support it.”

His advice: If you think you're sensitive to gluten, find out if you have celiac disease. That means a blood test for three antibodies and, if you have them, a biopsy.

Why you should test for celiac disease first

Going off gluten can make the antibodies temporarily disappear, which makes celiac harder to detect.

“If you have celiac disease, you need to know it, because you need to be gluten-free completely, and for life,” cautions Murray. “And your family members should be tested, because they’re at much higher risk for celiac disease.”

A gluten-free diet can be expensive, and it may be low in fiber or folate or other vitamins.

And you need to know that the treatment is working. “If someone has celiac disease, they have a damaged intestine,” says Murray. “We need to make sure that it recovers or you’re at increased risk for malignancies.”

Just trying a gluten-free diet might delay the correct diagnosis.

“I’ve seen patients who have had conditions like Crohn’s disease, and the diagnosis has been delayed because they were trying out a gluten-free diet,” says Murray. “Sometimes they felt better for a few weeks, and then their symptoms started to creep back again.”

It’s not surprising that some people feel better without gluten, he adds.

“They’re eating less, at least for a while, and they may be eating healthier because they’re eating less junk food. There’s also a placebo effect.”

The bottom line

“Test first, test right is the message. This is a chronic disease that requires lifetime treatment. It requires certainty,” says Murray.