Cutting out the middlemen—doctors or dietitians—food sensitivity tests variously ask for samples ranging from a drop of blood to strands of hair and, within weeks, shoot you color-coded charts or personalized microbiome reports straight to your inbox for your nerdy scrutiny.

With the Everlywell kit ($127), patients prick their finger and bleed onto a sample card. A prepaid shipping label ensures the tests arrive at Everlywell’s labs, where clinicians evaluate your IgG levels, or antibody responses to 96 different foods, from chia seeds to cantaloupe. If something (say, avocado) shows up red with “high reactivity” in your results, you may want to rethink that brunch order. Other kits, like the 5Strands ($88), test strands of your hair for intolerances. Both tests make it clear they cannot replace a food allergy test (IgE). For that, you’ll need a doctor.

You could create your own elimination diet with these tests’ results or enlist the help of your healthcare provider, as Everlywell encourages. Some registered dietitians, like San Francisco-based Sonya Angelone, say these tests just aren’t accurate. When it comes to at-home testing, “it’s like the wild, Wild West out there,” said Ms. Angelone, also a spokesperson for the Academy of Nutrition and Dietetics. “IgG is not a good measure for food sensitivity symptoms,” she said. The American Academy of Allergy, Asthma, and Immunology has also warned that IgG testing is not scientifically-backed and that higher antibody levels may actually indicate a tolerance for a food.

Five years ago, said Samino Qureshi, a Houston-based dietitian, none of her clients asked about food sensitivity tests. Now, they all do. “I have a lot of people coming to me saying, ‘Hey, I’ve taken this food sensitivity test and now I can only eat water and lettuce,” said Ms. Qureshi, who generally discredits the results and recommends, instead, starting small with a sensible elimination diet then reintroducing foods over time.

Everlywell says it endorses that same approach and stands by its tests, citing peer-reviewed research: “Antibody testing for food-related syndromes has been ordered by healthcare professionals for many years,” said the company. “We’ve heard from countless people that this test has helped change their lives for the better.”

Ms. Brown counts herself among them. She has now cut yeast from her diet but refuses to part with her beloved egg whites, despite Everlywell’s warning. A vegetarian, she needs protein, and eggs have never bugged her anyway. Her review: mixed. “I feel like I could have gone to a specialist in person and gotten more accurate and detailed results.”

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