It is important to keep your immune system in tip-top shape all the time because your body needs to be ready to defend itself when the time comes. Diet and lifestyle choices can impact how your immune system performs as you age. So you need to do what you can to make sure that your immune system is always in good shape. Eating a primarily plant-based diet is a good place to start. When it comes to boosting your immune system, you will want to focus on these foods.