Eating carbohydrates during intense exercise may help minimize exercise-induced immune disturbances and aid the body’s recovery, according to a research review of studies about exercise and immunity.

While regular, moderate exercise has been shown to have a positive effect on the immune system and overall health, it is believed that intense exercise can temporarily dampen the immune system, making exercisers more vulnerable to illness. Additionally, athletes who fail to give themselves sufficient time to recover between workouts or after upping the intensity of their workouts may be increasing their risk of illness. Researchers from Queensland University of Technology in Brisbane, Australia, looked at the available research to identify what factors could help minimize this risk. They determined that the best way to avoid unfavorable changes in the immune system following a workout was to consume carbs during or immediately after the exercise.

“Among various nutritional strategies to counteract immune depression during exercise recovery, carbohydrates have proven the most effective,” says Dr. Jonathan Peake, lead investigator of the study, which was published in the Journal of Applied Physiology. “Ingesting carbohydrates during vigorous exercise may help, because carbohydrates maintain blood sugar levels.” 

Dr. Peake goes on to explain that stable blood sugar levels help reduce the body’s stress response, which, in turn, moderates any undesirable mobilization of immune cells. “However,” cautions Dr. Peake, “more research is warranted to verify that this also helps to prevent infections and illnesses.” 

How Exercise Impacts the Immune System

According to the researchers, exercise can both increase and decrease the number of immune cells in blood.

“People often have fewer natural killer white blood cells after a workout, but we now believe they move to other parts of the body, rather than being destroyed,” explains Dr. Peake. “Exercise is a form of stress and more vigorous exercise creates more physiological stress, which causes physiological and biochemical changes in the body. To tackle the potential threats these changes highlight, the immune cells may simply move out of the blood stream to the lungs, for example.”

This still leaves exercisers’ bodies vulnerable to infections and, generally speaking, the more strenuous the exercise, the longer it takes for the immune system to return to normal.

“Epidemiological evidence suggests that regular moderate exercise protects against upper respiratory illnesses, like the common cold, whereas regular intense exercise increases the risk of upper respiratory illnesses,” explains Dr. Peake.

Dr. Oliver Neubauer, also of Queensland University of Technology, says the research suggests most people only need carbohydrates during high-intensity or prolonged exercise of 90 minutes or more. 

“The consumption of carbohydrates before and during strenuous exercise not only improves endurance performance,” explains Dr. Neubauer, “but it can also minimize exercise-related immune disturbances.”

So, how many carbohydrates should someone consume during a workout to help bolster their immune systems? “Between 30 and 60 grams of carbohydrates every hour during exercise help to support normal immune function,” says Dr. Neubauer. “Examples of carbohydrates that could be consumed during exercise include carbohydrate-containing fluids, gels and bars consisting of different carbohydrates such as glucose and fructose. Alternatively, bananas may also do the job.”

Of course, every person is different and what works or is tolerated by one may not be effective or another. Competitive athletes, in particular, should test out different foods or fluids prior to an event. “As general advice for people who train for, and participate in, endurance events, any products should be tested if they are tolerated in the field,” urges Dr. Neubauer.

Time also is critical: “Consuming carbohydrates in the first few hours immediately after strenuous exercise also helps to restore immune function,” says Dr. Neubauer. “This is especially important in situations where the recovery duration between two consecutive exercise sessions is short, which is often the case for athletes.”   

The researchers did not find sufficient evidence to advocate “immune-boosting” supplements such as antioxidants. Rather, they recommend following a diversified and well-balanced diet as the best approach to maintaining immune function following longer-term exercise training. And, not surprisingly, they recommend getting plenty of rest, although they believe more research is needed to understand the influence of sleep on immunity in athletes.