If you are thinking of trying an intermittent fast to lose weight, rethink your plan. A new study found that skipping breakfast may be bad for the immune system. Research shows that fasting, especially missing the first meal of the day, triggers responses in the immune cells of the brain that makes it more difficult for the body to fight off infection. That’s the conclusion from medical experts at Icahn School of Medicine at Mount Sinai Hospital in collaboration with a team from Harvard Medical School.

According to the Jerusalem Post, previous research has found that skipping meals or fasting for prolonged periods of time could also be tied to developing cardiovascular diseases and even some cancers. For the recent study, scientists used two groups of mice to examine the effects of fasting on the immune system. One group ate breakfast immediately upon waking, while the other group had no breakfast. Researchers took blood samples from the mice on set schedules ─ first thing after walking up, four hours later and then eight hours later.

The fasting group had an incredible 90% fewer monocytes in their blood at the four hour test and even less after eight hours of fasting. Monocytes are white blood cells made in bone marrow that travel through the bloodstream to fight infection. In the fasting mice, the monocytes returned to the bone marrow to hibernate. When food was introduced 24 hours later, the cells moved back into the bloodstream and became inflamed, making it hard to protect against infection. The researchers noted that the cells had become significantly changed in the fasting group while monocytes in the non-fasting group were unaffected, explained a news release from Mount Sinai.

According to New Scientist, the mice that fasted for 24 hours had more inflammation and were more likely to die from a bacterial infection than mice on a regular eating schedule.

“There is a growing awareness that fasting is healthy, and there is indeed abundant evidence for the benefits of fasting,” said Filip Swirski, lead author of the study and director of the Cardiovascular Research Institute at Icahn School of Medicine. “Our study provides a word of caution as it suggests that there may also be a cost to fasting that carries a health risk. The study shows there is a conversation between the nervous and immune systems.”

Swirski added, “Because these cells are so important to other diseases like heart disease or cancer, understanding how their function is controlled is critical.”