Immune function is "intimately linked" to nutrition, University of Newcastle Professor Clare Collins says.
Amid coronavirus concern and the approach of flu season, Professor Collins said it was a good time for people to "try to make sure their immune system is in top gear".
The professor of nutrition and dietetics used a car analogy to illustrate her point.
"You're doing a road trip but you're not sure what the road is like ahead," she said.
"What do you do before you head out on the road? You prepare. And you probably get your car serviced."
She listed a group of nutrients that contribute to good immune function and help people protect against viruses.
"The big guns are vitamin A, zinc, iron and phytonutrients with an antioxidant role like beta carotene, vitamin C, B vitamins, selenium and copper."
Research showed that people with deficiencies in these nutrients find it harder to recover from viruses.
"Vitamin A is essential to the cells that line mucosa in your lungs, nose and mouth.
"If you don't have enough vitamin A, viruses have a better chance of getting through your first line of defence. It's like you have no front row in your football team."
Good sources of vitamin A are cheese, eggs, oily fish, milk and yoghurt.
Plant sources of vitamin A include yellow, orange and dark green vegetables like carrots, pumpkin, sweet potato, spinach and broccoli.
Professor Collins said iron was "really important".
"If you're low in iron right at the time when you're hit by a virus, you can't ramp up, you can't call on the back row to come and help the front row forwards," she said.
Iron deficiency lurks in many people, especially women and children.
"They are more likely to be hit harder by any sort of viral infection," she said.
Sources of iron include lean red meat, chicken and fish. Plant iron is found in beans and lentils. Iron can also be obtained from fortified breakfast cereal.
Professor Collins prefers food over supplements, but said those who have had an iron deficiency should get their iron status checked and take supplements if needed.
"The other big mineral is zinc. It's often overlooked. You need zinc for making DNA. You can't make a new cell unless you have zinc.
"Oysters are a really rich source of zinc. Half a dozen oysters will take care of your zinc requirements for the week. For oyster lovers, let your hair down."
Seafood generally is a good source of zinc. Vegetarians can get zinc from tofu, miso, legumes, wheatgerm, wholegrain foods and nuts.
She said phytonutrients with antioxidant properties were "important once you get an infection".
During an infection, free radicals cause damage to the body. It's like playing tennis when a machine that fires tennis balls is unexpectedly turned on.
"You've got to try and defend yourself or you're going to get hurt," she said.
"When there's an infection in your body, free radicals punch through the walls of cells, making the contents of those cells leak and cause a metabolic mess that needs to be cleaned up."
Nutrients that have an antioxidant effect can clean this mess up.
"We call them phytonutrients - that's things like beta carotene, vitamin C, selenium, copper and riboflavin."
Vitamin C sources include mangoes, kiwi fruits, limes, strawberries, capsicum, broccoli, spinach and tomatoes.
"We're starting to see a recurring theme because nowhere have I said cheeseburgers or pizza," she said.
"The recurring theme is good old fashioned basic foods."
She said some people might consider rushing out and buying supplements to get the vitamins and nutrients mentioned.
"The problem with doing that is you can get your metabolism out of kilter," she said, adding that greatly increasing the intake of one vitamin or nutrient could trigger a deficiency in another.
"Having them predominantly from foods is one way of making sure you get them in proportional amounts."
Those that require a multivitamin should take a general one that "contains small amounts across the broad spectrum", rather than "buying 10 bottles and spending $150, giving yourself a rare deficiency and leaving yourself more vulnerable".
She added that research, along with mum's advice, showed hot chicken soup with vegetables has some immune-enhancing properties.
Check out the spicy chicken soup and other recipes at nomoneynotime.com.au.
