Foods That Boost Immunity During Flu Season - as part of the nutrition series by GeoBeats. During flu season, it can be helpful to try to boost your immunity with certain foods. First of all the winter fruits of oranges and grapefruit are wonderful because they are loaded with the nutrient vitamin C. Vitamin C really helps your immune system. So try to get lots of fruits and vegetables throughout the day. We all need 5 to 9 servings, in fact, of fruits and vegetables. Protein is also really important to keep our immune system up. And you want to have about 20, 15 to 20 grams of protein in each meal throughout the day, and a snack. Eating foods that naturally have probiotics, or supplementing your diet with a probiotic supplement can also help keep your immunity up during the cold and flu season. An example of that would be cultured yogurt. Any yogurt that has live cultures in it is going to be a probiotic and keep your digestive system healthy. You can also buy supplements too that you can take daily that actually feed those healthy bacteria in your colon to protect your immune system.