DENVER -- Many people experience nasal congestion, indigestion, and diarrhea during the holidays that might not be flu or cold-related at all. Instead, they might be caused by our favorite holiday foods such as turkey stuffing, dinner rolls, pumpkin pie, and cookies.

The culprit could be gluten, a protein found in the wheat flour used to make these holidays foods, says Carol Fenster, Ph .D., an authority on gluten-free cooking.

Symptoms like those above and other reactions -- including fatigue, skin rashes, stomach aches, and migraine headaches -- often increase during the holidays because most holiday foods contain wheat.

"Reactions to wheat should be taken seriously," says Carol Fenster, Ph .D., who develops gluten-free products for manufacturers. "Chronic sinus congestion can lead to infection and eventually antibiotics. People who are merely intolerant to wheat become mildly ill. But for those with true wheat allergies, wheat can be fatal."

In addition, many Americans -- 1 in every 133, according to the National Institutes of Health -- have a little known, but increasingly common autoimmune condition called celiac disease. The gluten in wheat (and related grains such barley, rye, and spelt) inhibits absorption of nutrients from food and, left untreated, celiac disease can lead to anemia, osteoporosis, lymphoma, and even death.

"People can be sensitive to wheat and not even know it. Testing by a qualified health professional is required to identify wheat or other common food culprits such as milk or eggs," says Fenster, who wrote Gluten-Free 101 and 6 other gluten-free cookbooks since discovering her own sensitivity 18 years ago. "An allergist diagnoses allergies; a gastroenterologist diagnoses celiac disease."

Fenster offers tips for indulging in your favorite holiday foods without unwanted symptoms:

-- Purchase gluten-free foods at your local health food store or obtain them via mail-order
-- Make your own food with cookbooks that use substitutes for the offending ingredients
-- Offer to bring a gluten-free dish to holiday get-togethers