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As athletes, we know that in order to boost performance we need to train hard. We aim for a balanced training plan that places a significant amount of training stress on the body to elicit performance gains but adequate rest to keep the body in good health.
When an athlete trains too much (intensity or volume), the immune system is suppressed. Often, the athlete will feel he/she needs a few extra days of rest to recover from a dampened immune system but most of the time, it's not that easy to just rest, get more sleep and feel "normal" again.
So for athletes who have been in this situation where the raining load is too much for the body or individual lifestyle, you may be surprised to know that these athletes often experience a host of GI issues in training, racing and throughout the day. These athletes often seek extreme modifications in the diet, often to the point of elimination sport nutrition before, during and after workouts or avoiding healthy foods. But in reality, it's not always the diet that is causing the unhappy gut feelings - remember, the immune system is a critical component of gut health!
Additional, with gut healthy foods, you have a greater chance of boosting performance as the body will be in optimal health when you place intentional training stress on it in training/racing.