CHICAGO (AP) _ Researchers at the University of Chicago have made if official: You are, indeed, what you eat.

The researchers said they have established a definite link between food and moodiness, including irritability, anxiety and depresssion.

But it is too early to pinpoint particular foods as the source of certain moods, Dr. John Crayton, an associate professor of psychiatry who directed the study, said Thursday.

Although doctors still don't understand how, the food-induced moodiness also appears related to changes in the body's immune system, which fights disease, Crayton said.

''We're not talking about what might be called 'traditional' food allergies, such as breaking out in hives or a rash after eating certain foods, but marked changes in mood and behavior,'' he said.

''Such a link has long been theorized but it has seldom been studied and almost never shown,'' he said.

Crayton's group studied 35 volunteers who were fed controlled diets of capsules containing powdered wheat, milk, chocolate and a placebo over eight days.

The volunteers included 23 psychiatric patients who had complained of food sensitivity in the past, and 12 healthy people with no such complaints.

Neither the researchers nor the participants knew the capsules' contents until the project was completed, Crayton said.

Among the 23 volunteers who had histories of food complaints, 16 developed marked mood and behavior changes, and they showed alterations in their immune systems as well, he said.

Mood changes were linked to wheat and milk, but chocolate was less likely to cause anxiety, irritability or depression, he said.

The immune system changes included a higher level of proteins that help control the immune system's reactions, and lower levels of proteins formed in the course of an immune system reaction, Crayton said.

One theory about the relationship, he said, is that substances formed during an immune system reaction cause local swelling of the brain, which could trigger mood swings.