Having worked with elite athletes and services members, I know firsthand how important it is to take care of your immune system so you can perform at your best. As the previous sports dietitian for Florida State Athletics and the US Army Special Forces, I have seen how exercise regimens and diets can strain our ability to stay healthy. Now, as an Assistant Professor in Nutrition at Appalachian State University, I focus on researching sports nutrition with the goal of improving health and performance by examining how nutrition influences metabolism, inflammation, and immune function during exercise.
Most people do not appreciate the complexity and functionality of an optimized immune system until it is challenged. A healthy immune system provides a multi-layered defense against microscopic invaders such as bacteria, viruses, and fungi as well as protection against excessive oxidative stress.
Innate vs. Adaptive Immunity
The immune system is organized into to two arms: innate and adaptive immunity.
- Innate immunity is a rapid, non-specific response designed to rid the body of invading microorganisms through protective barriers and attack cells.
- Adaptive immunity is a slower, highly specialized response that builds on subsequent exposures to a pathogen. Vaccines target adaptive immunity, stimulating the production of memory cells and antibodies that will respond to future antigen exposure.
Overall, the innate and adaptive immune cells work together to eliminate threatening microorganism and minimize the risk of infection. (Reference https://www.ncbi.nlm.nih.gov/pubmed/29637836)
What Goes Into A Healthy Immune System?
A healthy immune system depends on many factors. Exercise and nutrition are critical factors to maintaining a healthy immune system.
Research has shown that moderate exercise (intensity less than 60% maximal oxygen capacity for duration less than 60 minutes) has protective effects on immune function by strengthening the response of both innate and adaptive cells.
On the other hand, vigorous exercise stimulates the release of stress hormones, which suppresses immune function during the recovery period, persisting up to several days in some cases. For individuals engaged in exercise exceeding 60 minutes, carbohydrates are especially important for attenuating post-exercise inflammation and immune suppression.
The Proper Foods Fuel A Healthy Immune System
Consuming carbohydrates during running or cycling activity has consistently been shown to increase glucose and insulin concentrations, which reduces stress hormones released during exercise (i.e., cortisol and epinephrine) to modulate the release of inflammatory cytokines and immune cells.
It is worth noting that many whole food fruits (bananas, blueberries, pears, watermelon) have a similar effect on immune response to commercial sugar beverages and may have additional health benefits due to their high polyphenol content. Polyphenols are a class of high antioxidant compound found in many fruits, vegetables, teas, whole grains, nuts, seeds, and legumes. (Reference Nieman, D.C.; Wentz, L.M. The Compelling Link Between Physical Activity and the Body’s Defense System. JSHS 2018, accepted, in press.)
There’s A Connection Between Dieting and A Healthy Immune System
Diets low in carbohydrates may inhibit optimal function of the immune system, especially in active individuals. For example, the keto diet eliminates nearly all sources of carbohydrates, including polyphenol-rich fruits and vegetables and may therefore impair immune function, limiting the body’s natural ability to modulate oxidative stress and inflammatory pathways.
The Keto Diet Can Limit Intake of Essential Vitamins and Minerals
In order to produce ketones, the diet’s namesake, one has to limit protein intake as well as carbohydrates. Protein breaks down in into some amino acids, and some of these can make glucose (i.e., sugar) in the blood. If there is circulating blood glucose, then ketones will not be produced, and the body is not in ketosis.
Thus, to follow a keto diet that stimulates production of ketones and increase the oxidation of fatty acids, one must consume a diet of mostly fatty foods that also increase inflammatory pathways and limit intake of essential vitamins and minerals such as vitamin C (found in citrus fruit and many vegetables) and zinc (found in fish, meats, and whole grains).
Be Sure To Get Your Fruits and Vegetables If You’re On The Whole30 Diet
The Whole30 diet is less restrictive than the keto diet, but it limits intake of grains, dairy, legumes, and sources of sugar, all of which are carbohydrate sources. Therefore, individuals following this diet will need to pay special attention to ensuring fruits and vegetables provide adequate carbohydrates, vitamins, and minerals to optimize immune function.
Mediterranean and DASH Diets Have You Covered
On the other hand, the Mediterranean and DASH diets emphasize not only heart healthy but also immune healthy foods such as fish, fruits, vegetables, nuts, legumes, dairy, and plant oils. These foods are rich in polyphenols, anti-inflammatory omega-3 fatty acids, vitamin C, and zinc. These diets fit well into a flexitarian lifestyle, focusing on a majority plant-based diet but still including animal meats and dairy.
Know What You’re Limiting Before Choosing A Diet
Many types of diets are based on the premise of calorie restriction for weight loss, whether by counting total calories (i.e., Weight Watchers) or restricting entire food groups (i.e., Keto, Whole30).
Losing weight is a product of an energy imbalance, whereby the calories expended exceed calories consumed. However, a diet that fuels weight loss does not necessarily equal a nutrient-rich diet, and nutrients essential to immune function may be missing if fruits, vegetables, and proteins are restricted or eliminated.
Finally, in addition to consuming a nutrient-rich diet and engaging in regular physical activity, other strategies to enhance immune function include consumption of adequate fluids (2-5 liters/day), sufficient sleep duration and quality (7-9 continuous hours/night), avoiding excess stress, and minimizing exposure to infectious microorganisms by washing hands and receiving necessary vaccinations. (Reference https://www.ncbi.nlm.nih.gov/pubmed/21446353)