Eating healthy is always a good idea but it's especially important during cold and flu season. Certain foods can keep your immune system in fighting form.

Vaccination isn't the only weapon you have against the flu. Your grocery store is stocked with ammunition.

"There are a whole bunch of various components called phytochemicals in food which keep you healthy," said Dr. Ara Dermarderosian.

He’s a pharmacognosist, an expert in the branch of pharmacology that deals with drugs in their crude or natural state and with medicinal herbs or other plants.

Plants produce the chemicals to protect themselves but this expert in natural medicine says they also protect humans from disease by boosting the immune system.

"Garlic and onion are at the top of the list as far as qualities for keeping you well," said Dermarderosian.

Forget bad breath. Those smelly compounds in garlic and onions can help ward off bacteria and viruses.

"It's shown in many studies, where they consume considerable amounts of garlic or onions, they have a lower incidence of upper respiratory tract infections," said Dermarderosian.

Mushrooms are also high on the must-have list. They contain compounds that stimulate the production of so-called 'natural killer' cells that fight infection.

"Articles in the Journal of Clinical Nutrition show that this is very, very effective in helping stave off the flu."

Other edible germ fighters include citrus fruits, yogurt with active cultures, and green tea. Also protein rich foods like salmon and chicken. If you prefer supplements, try black elderberry extract.

It's food for thought that could give your immune system a real shot in the arm during flu season.

Other supplements that might keep flu symptoms at bay include: zinc, ginseng and vitamin D.