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Milk was a "bad choice" for Justin Bieber, who blamed it for making him vomit onstage Saturday night in Arizona, but it's an even worse choice for the 1.3 million children who have milk allergies.

New Zealand researchers say they've found a way to genetically engineer cows to produce hypoallergenic milk, but others say that's too good to be true.

Researchers at the University of Waikato interfered with cows' RNA (the acid that passes DNA's genetic "instructions" to proteins) to select for genes that would decrease the cow's output of BLG, a protein not present in human milk, to which 2 to 3 percent of people are allergic, according to the study.

Immediate symptoms of milk allergies can include hives, wheezing and vomiting, according to the Mayo Clinic. Symptoms that take longer to develop may include diarrhea, abdominal cramps, a skin rash around the mouth and a runny nose.

But the so-called hypoallergenic milk eliminates one allergen only to increase another, researchers not involved with the study say.

The RNA "fine-tuning" resulted in a 98 percent BLG "gene knockdown," but it didn't decrease the milk's overall protein content, according to the study. As the BLG protein levels dropped, casein proteins - which are naturally found in cows' milk anyway - increased.

Dr. Scott Sicherer, a professor and researcher at the Jaffe Food Allergy Institute at Mount Sinai Hospital in New York, said BLG is just one of the proteins in bovine milk that cause allergies in humans. Many humans are allergic to multiple milk proteins, especially casein.

"Casein, actually, is the major milk protein that we believe causes most of the severe milk allergies," he said. "Creating a milk enriched with casein proteins would seem problematic given what we know about milk allergy."

According to Sicherer, 13 to 76 percent of patients react to BLG, compared with 92 percent to 100 percent of patients who react to caseins.

The University of Waikato researchers not available for comment.