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Should you try at-home food sensitivity tests?

The tests are widely available, but experts are skeptical of the results.

You've probably come across an online ad for food sensitivity tests and wondered if a kit like that could help figure out where digestive issues are coming from. Without a prescription or a doctor's appointment, the tests claim they can give you some clues about what's to blame for bloating, diarrhea and more.

But, as NBC News senior consumer investigative correspondent Vicky Nguyen found out, there’s not much evidence that home food sensitivity tests can really tell you very much.

What it's like to take a food sensitivity test

Nguyen tried three tests: One from Everlywell, which is currently selling for $127 on the company's site and relies on a blood sample. The second test, from 5 Strands, is priced at $88 on their site and required her to pluck out 15 strands of hair from the back of her neck. And the third test, which also required a hair sample, is from Ucari and costs between $69 and $99. Nugyen sent her samples to each company and received her results within two weeks.

Her results from Everlywell suggested she has a "high reactivity" to dairy milk. Test results from 5 Strands listed more than 75 foods, such as limes and almond milk, as "severe intolerances." And Ucari's test found 10 "severe intolerances," including rice milk, roasted peanuts and chives.

So, how reliable are these results?

Blood tests like Everlywell's work by measuring antibody responses to different foods. Hair tests like those from 5 Strands and Ucari rely on measurements of bioresonance, a concept used in alternative medicine, to compare frequencies found in hair to those in foods.

But neither of these techniques is proven to actually detect food sensitivities or intolerances, Stacy Cavagnaro, a registered dietitian at the Cleveland Clinic, told Nguyen. In fact, the American Academy of Allergy, Asthma and Immunology recommends against using tests like these to diagnose food allergies, sensitivities or intolerances.

"When a patient is asking me about this, I personally say, ‘I wish that these worked.’ Because it would make my job a lot easier," Cavagnaro said. She doesn't see much value in tests like this "because the science behind it has not been proven to be accurate."

Everlywell and 5 Strands told NBC News in a statement that the two tests shouldn't be compared to each other because the two techniques are so different.

Additionally, Everlywell said that its antibody testing is a "well-established methodology used for a wide range of clinical testing" and noted that its test results should be shared with a doctor to help guide an elimination diet.

5 Strands also added that there are other factors that may affect its test results, such as when the samples are analyzed. The company said that, because bioresonance isn't taught in medical school, some doctors and other experts may not necessarily be aware of the evidence behind it.

Food allergies are not the same as intolerances or sensitivities.

It's important to note that these tests cannot detect or diagnose food allergies. Symptoms of a food allergy can include hives, itching in the mouth, swelling of the lips or face, wheezing and fainting, the Mayo Clinic says.

Sometimes food allergies also cause gastrointestinal symptoms, the AAAAI says. But in the case of a food intolerance or sensitivity, gastrointestinal symptoms are frequently the only signs present. In fact, Cavagnaro said there isn't really a specific medical or diagnostic definition for "food sensitivity."

What's the best way to find out if you have issues with certain foods?

Of course, some people simply find that they feel better physically if they don’t eat certain foods, or they may decide to not eat certain ingredients (like meat) for ethical or other reasons. But the only truly reliable way to find out if you have a food intolerance is to embark on an elimination diet, Cavagnaro said.

Unfortunately, if you want to do an elimination diet properly, it will take a lot of time and effort. An elimination diet typically involves removing a specific food or group of foods from your diet for a period of time to see how your symptoms (such as bloating, diarrhea or constipation) might change. In some cases, like if you have a true food allergy, you might have to stop eating that food permanently.

If you're interested in trying an elimination diet — or making any other major changes to your food habits — it's worth checking in with a medical professional for guidance first. Home food sensitivity tests might be a useful or interesting experiment if you have the cash to spend. But the results from those tests shouldn't be used on their own to make major dietary decisions.