“Think of probiotics as the ‘good bacteria’ in the gut, helping influence the microorganisms that live in the digestive tract,” explains Weiler. While you can buy probiotic supplements, a 2017 study published in Nutrients found that daily consumption of probiotic-rich yogurt can improve immune function by increasing the activity of natural killer cells, or cells that limit the spread of disease. Be sure to pick up containers free of excess added sugar—plain varieties (which you can flavor with cinnamon and fresh fruit) are your best bet, but anything with less than 8 total grams of sugar is a wholesome option.
Oats and barley
These grains contain beta-glucan, a type of fiber that helps fight disease by stimulating immune cells, research shows. Fiber in general also provides nourishment for healthy gut bacteria to thrive and thus support the immune system, Weiler explains.