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Nutrition for Immunity: Spotlight on Colorful Produce

March 25, 2020, 1:24 p.m. (ET)

Nutrition for Immunity: Spotlight on Colorful Produce

By Kelsey Smith, MS, RDN, METS I


Given the current global climate with COVID-19, many people are asking “What can I do to improve my immune system?”


While there is no substitute for appropriate hand washing and social distancing, what goes in our bodies can either enhance or diminish our immune function. Beyond virus pandemics, focused attention on key foods will help athletes recover from strenuous training. Over the coming weeks, we'll introduce some principles for improving immune function and reducing inflammation. Up first is increasing your daily fruit and vegetable consumption.


Why Produce is Powerful


Shocking! A Registered Dietitian is recommending that you eat fruits and vegetables. Stay with me as I explain why they are so important. It all starts with oxidative stress, or the imbalance of free radicals and antioxidants in the body. Why do we care about this? Too many free radicals and not enough antioxidants can lead to cellular damage and chronic inflammation. Over time, this inflammation results in early aging, cardiovascular disease, cancer and more. Got your attention now didn’t I?


Fortunately, fruits and vegetables are antioxidant powerhouses, containing vitamins A, C, E, and more. Research tells us that eating more antioxidant rich produce is better. In one study, elite endurance athletes training at altitude were either prescribed a diet with double the amount of antioxidant rich foods that they typically consumed, or a low antioxidant control diet. At the end of three weeks, the athletes in the increased antioxidant diet group had elevated antioxidant capacity (as seen in FRAP), and decreased inflammatory biomarkers (noted by IL13 and micro-CRP) compared to control participants. Similarly, one meta-analysis reported that higher fruit and vegetable intake decreased circulating levels of C-reactive protein (CRP) and tumor necrosis factor (TNF), both of which are markers of inflammation. In fact, greater fruit and vegetable intake is associated with decreased risk of death from all causes.


Other substances in fruits and vegetables garnering a lot of attention are called phytochemicals. While their role is not fully understood, we do know that phytochemicals act similarly to antioxidants and can help protect against oxidative stress and chronic inflammation. Interestingly, phytochemicals contribute to the color of fruit and vegetables, which often indicates nutrient content. For example, yellow or deep-orange vegetables, such as winter squash and sweet potatoes, are excellent sources of carotenoids, or precursors of vitamin A. Blue and purple foods get their hue from their anthocyanin content, a potent phytochemical. Examples include blueberries, eggplant, pomegranate, and plums. “Eating the rainbow” isn’t just a cute phrase; it’s actually an excellent strategy for maximizing your health.


To Supplement or Not to Supplement


If antioxidants are so great, it may be tempting to load up on vitamin and mineral supplements. There are some cases when a little boost might be warranted. Higher dose vitamin C supplementation might reduce the occurrence of the common cold in individuals undergoing heavy physical stress, as well as decrease common cold duration. Zinc research is variable, but zinc consumed within 24 hours after the onset of common cold symptoms might help reduce both the duration and severity of the illness. However, most people do not need extra supplementation if already consuming the USDA recommended 5-9 servings of fruits and vegetables per day. Still not convinced? Consider that high dose antioxidant supplementation, like vitamin C and E, might actually blunt endurance training adaptations. When in doubt, aim for a consistently high intake of colorful fruits and vegetables.


How to Incorporate More Fruits and Vegetables


When looking to add more fruits and vegetables to the diet, start with what is in season. Seasonal produce will be tastier and potentially higher in overall nutrition value. We’re currently in the transition from winter to spring, so you may see some changes in availability, but some produce in your area might include: winter squash, sweet potatoes, carrots, beets, cabbage, brussels sprouts, broccoli, kale, rutabaga, onions, garlic, and cauliflower, citrus (orange, lemon, grapefruit), and kiwi. The USDA’s seasonal produce guide is an excellent resource. No fresh produce? No problem. Frozen fruits and vegetables are a great substitute as they are inexpensive and harvested at their peak season.


Here are ten ways to add more produce to your diet:

1.     Layer greens, shredded carrots, avocado and sprouts on sandwiches.

2.     Blend roasted peppers, sweet potatoes, or squash into pasta sauce.

3.     Toss riced cauliflower into casseroles or even smoothies (you won’t taste it!).

4.     Add kale or spinach to soups, smoothies, and sauces.

5.     Build a robust omelette with onions, mushrooms, spinach, or bell peppers.

6.     Dip raw carrots, peppers, or snap peas in hummus, guacamole or Greek yogurt dip.

7.     Layer fresh or roasted veggies on top of whole grain pizza.

8.     Stir fresh or frozen berries into oatmeal or yogurt.

9.     Double the amount of vegetables called for in a specific recipe.

10.  Add grated zucchini, onions, or carrots to burger or meatloafs.


When it comes to adding more produce to your diet, give yourself permission to experiment. You might just surprise yourself with how tasty and versatile some produce, especially vegetables, might be. Just remember that whether you are looking to beat disease or enhance your training, increasing fruits and vegetable intake is always in season.


Kelsey Smith is a Registered Sport Dietitian at eNRG Performance ( Based out of Colorado, she works with endurance athletes all over the world and is a specializes in periodizing an athlete’s nutrition plan to support optimal health and performance. Contact her at


The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.



References and Resources:

1.     Color Me Healthy - Eating for a Rainbow of Benefits. (2008, November). Retrieved March 2020, from

2.     Douglas, R., Hemilä, H., Chalker, E., Dsouza, R., & Treacy, B. (2004). Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews. doi: 10.1002/14651858.cd000980.pub2

3.     Hosseini, B., Berthon, B. S., Saedisomeolia, A., Starkey, M. R., Collison, A., Wark, P. A. B., & Wood, L. G. (2018). Effects of fruit and vegetable consumption on inflammatory biomarkers and immune cell populations: a systematic literature review and meta-analysis. The American Journal of Clinical Nutrition, 108(1), 136–155. doi: 10.1093/ajcn/nqy082

4.     Koivisto, A. E., Olsen, T., Paur, I., Paulsen, G., Bastani, N. E., Garthe, I., … Bøhn, S. K. (2019). Effects of antioxidant-rich foods on altitude-induced oxidative stress and inflammation in elite endurance athletes: A randomized controlled trial. Plos One, 14(6). doi: 10.1371/journal.pone.0217895

5.     Paulsen, G., Cumming, K. T., Holden, G., Hallén, J., Rønnestad, B. R., Sveen, O., … Raastad, T. (2014). Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomised, controlled trial. The Journal of Physiology, 592(8), 1887–1901. doi: 10.1113/jphysiol.2013.267419

6.     Science, M., Johnstone, J., Roth, D. E., Guyatt, G., & Loeb, M. (2012). Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials. Canadian Medical Association Journal, 184(10). doi: 10.1503/cmaj.111990

7.     Seasonal Produce Guide. Retrieved from

8.     Wang, X., Ouyang, Y., Liu, J., Zhu, M., Zhao, G., Bao, W., & Hu, F. B. (2014). Fruit and vegetable consumption and mortality from all causes, cardiovascular disease, and cancer: systematic review and dose-response meta-analysis of prospective cohort studies. Bmj, 349(jul29 3). doi: 10.1136/bmj.g4490