Doctors always restrict the diet of patients undergoing treatment for blood cancers, to protect them from foodborne illnesses while their immune system is knocked down.

That remains a wise course of action, a new study says.

A diet designed to limit exposure to foodborne pathogens effectively protects patients receiving treatment for leukemia from serious infections, according to results published Dec. 17 in the Journal of Clinical Oncology.

“Given the evidence from this study, we cannot change the current standard of care,” said co-lead researcher Ji-Hyun Lee, a professor of biostatistics in the University of Florida College of Public Health and Health Professions.

“This study provides truly critical information for patients who are vulnerable to infection,” Lee added in a news release.

The results come at a time when some doctors have questioned whether the diet — which prohibits raw fruits and veggies, unpasteurized dairy and undercooked animal protein — is overly restrictive and could contribute to poor nutrition among people undergoing intensive cancer therapies, researchers said.

This “neutropenic” diet is named after neutropenia, a condition in which people have low levels of white blood cells called neutrophils, researchers said in background notes.

Chemotherapy suppresses these cells, increasing infection risk, researchers said. The most serious infection risk comes from gastrointestinal (GI) diseases caused by microbes in uncooked foods.

However, the neutropenic diet has been in place for more than a half-century without any clinical trial results to back it up, researchers noted.

For the new study, more than 200 hospitalized patients with leukemia were randomly assigned either the neutropenic diet or a more liberal diet while undergoing either chemo or a stem cell transplant.

The more liberal diet encouraged at least one serving of fresh fruits or vegetables each day, and allowed patients to eat pasteurized yogurt.

Results showed that more than 31% of patients on the liberal diet wound up with a major infection, compared with 20% of those on the neutropenic diet.

In fact, the trial was halted early because major infections were occurring so much more often among people on the liberal diet, researchers said.

The trial also found that patients in both groups did not eat enough calories for good nutrition, likely caused by treatment side effects that cause nausea and appetite loss.

“We still need to come up with better approaches to improve the nutrition of these patients without compromising their safety,” co-lead researcher Dr. John Wingard, a professor emeritus of medicine at the University of Florida, said in a news release. “We recognize how important good nutrition is for the gut microbiome and patient outcomes.”