Fall is in the air, and so are an increased number of viral pathogens.

Flu activity usually begins to pick up its pace in October, according to the Centers for Disease Control and Prevention (CDC), and many of us will have already experienced the first trace of a sore throat or stuffy nose that heralds the beginning of the cold and flu season well before then. Clearly, now is the time to start building your defences. A healthy immune system depends on a lot, including quality sleep, solid hygiene, stress management and, not least of all, a well-balanced diet.

Up to 80% of the body’s immune cells are found in the gut, and experts increasingly understand that what you eat affects the unique mix of friendly bacteria in the GI tract known as the microbiome, which influences overall immunity.

“The immune system is a complex network of organs, tissues and cells,” said Dr. Carlos Zambrano, a board-certified infectious disease physician and the head of the COVID-19 task force at Loretto Hospital in Chicago. “Clinical deficiencies of [some key] nutrients can weaken immunity and increase susceptibility to infections.”

Nearly half of American adults fail to meet the most basic dietary guidelines. “So even a little boost can help,” said registered dietician Toby Amidor. While she cautions that there is no “magic bullet” food or drink that will “boost your immune system through the roof,” the following are foods that nutrition and infectious disease experts keep stocked in their own pantries. Find out why and what to add to your grocery shopping list.

This bulb has both anti-inflammatory and immune-boosting properties.

“It works to upregulate certain chemicals in the immune system responsible for fighting viruses and bacteria and also targets inflammatory cells,” said Dr. Tania Elliott, a spokesperson for the American College of Allergy, Asthma and Immunology.

While heat can destroy some of those benefits, researchers at Penn State University found that crushing or chopping the cloves activates their main bioactive compound. So, if you want the benefits without the bite of raw garlic, chop it and let it sit for 10-15 minutes before cooking.

While people default to citrus as a source of vitamin C, green or red chilies (serrano, jalapeño, poblano) have nearly as much of this potent antioxidant, which has antiviral properties and may stimulate antibody production, which may help fight off bacterial infections when you have the flu, according to Dr. John La Puma, author of ChefMD’s “Big Book of Culinary Medicine.”

“You should have vitamin C-containing foods twice daily so you can fully absorb it,” he said. As a bonus, Elliott said that spicy foods contain capsaicin, a compound that can thin out mucous, making it less habitable for inflammation-causing viruses and bacteria.

Like garlic, this root has antiviral and antibacterial properties and may be especially good at warding off or soothing a sore throat. One in vitro study found that a ginger solution was effective against three pathogens that commonly cause throat infections, and another found a ginger solution comparable to antibiotics in treating the bacteria that cause strep throat.

“Ginger contains gingerols, compounds that act as anti-inflammatories,” Amidor said. Studies have tested ginger extract in amounts from 20g/100mL to 100g/100mL and indicate more is better, so grate or slice some fresh ginger into soups, smoothies, broths or tea for the benefits.

Amidor likes to keep these on hand for snacking because they are a potent source of vitamin E and several minerals related to immunity. Not having adequate vitamin E is associated with reduced activity of white blood cells, which normally keep invading viruses from spreading, Zambrano noted. Sunflower seeds also contain magnesium, and skimping on that mineral is associated with decreased immune cell activity, increased oxidative stress and increased inflammation, according to recent research.

Most people struggle to get enough vitamin D, particularly in the colder months. “In winter, too little vitamin D is made in your skin because the angle of the sun is too low,” La Puma said.

Harvard researchers found that people with low levels of this nutrient were about 40% more likely to have had a recent respiratory infection compared with individuals who had plenty of vitamin D. This may be because vitamin D triggers the production of antimicrobial compounds that can help neutralise the activity of infectious agents, including the influenza virus.

Salmon is one of the best sources of this nutrient, with one 3.5-ounce serving to deliver two-thirds of your daily value of D per USDA data, and shelf-stable cans or pouches make adding some to a salad or spreading on crackers easy.

Zambrano’s sweetener of choice is a specific kind of honey produced by bees in New Zealand. Manuka honey has antibacterial properties and contains a natural compound that can help with cough as well or better than over-the-counter cold medicines, according to research.

Too much salt in your diet can get a bad rap, but Elliott likes to have coarse sea salt on hand to soothe a sore throat. “Gargling with warm salt water when you are sick, especially sea salt, can have an anti-inflammatory effect,” she said. “It works by helping to wash away viruses, bacteria, allergens and mucus in your throat. The rougher the salt, the better.”

One study found that participants who gargled with sea salt reduced the duration of their colds by an average of nearly two days, reduced their use of over-the-counter cold medicine by more than one-third, and were less contagious to members of their household.

“Hydration is such an important part of supporting your immune system,” said Glassman, “and people often aren’t drinking as much as they do in the summer.” Her solution is to stock up on tea. She especially likes turmeric tea, which contains the compound curcumin, an anti-inflammatory.

One study found that consuming curcumin for 12 weeks reduced the time healthy Japanese adults experienced cold symptoms. La Puma likes green tea, which he says has been shown to lower the viral protein production of cells infected with the influenza virus. He explained, “Catechins in green tea change the physical properties of the viral membrane and block a protein, called hemagglutinin, from the flu virus so the virus cannot be absorbed into your cells.”