In a healthy digestive system, the cells that form the paper-thin lining of the small and large intestines are packed very closely together. In fact, they’re so close that only what should pass through — digested food and water — can enter the bloodstream.

But the tight junctions of the gut lining can easily be disrupted and become too porous. Antibiotics, diets high in chemical-laden processed foods, sugar, alcohol, anti-inflammatory drugs such as aspirin and ibuprofen, food intolerances, and many other dietary factors can damage the gut lining and force it to become more permeable.

These same factors also affect the balance of both the trillions of beneficial and harmful bacteria in the gut. When this balance is disturbed, harmful bacteria can get the upper hand and cause an increase in gut permeability.

The result is commonly referred to as “Leaky Gut Syndrome,” a condition that allows toxins, bacteria, undigested food particles, and other undesirable gut contents to enter the bloodstream and circulate to the rest of the body.

A leaky gut can cause systemic inflammation. Because of this, the immune system may not protect the body as well as it should, leading to fatigue as well as joint and muscle aches. Digestion is also adversely affected, and people with leaky gut often complain of bloating, cramps, and diarrhea.

Over time, chronic inflammation can lead to musculoskeletal problems such as osteoarthritis, changes in body composition, and increased risks for diabetes and heart disease.

Athletes have another source of leaky gut syndrome: overtraining. When an athlete works out hard over a long period of time, he or she puts a lot of stress on the gut. Blood that’s needed for digestion gets diverted to the rest of the body — and the flow doesn’t necessarily get restored quickly enough when the workout is completed.

In addition, the stress of working out and hard training over several weeks — in preparation for a big tournament, for example — puts the athlete at risk for developing a leaky gut. Studies have shown that workouts longer than two hours can be damaging to the gut.

When the gut is compromised, it impacts the immune system. That’s why training too hard can lead to more easily catching a cold or stomach bug.

It’s also why training too hard can be counterproductive to building strength and endurance. When training damages the digestive system, the ability to absorb and utilize nutrients efficiently is rapidly diminished and the body is being deprived of the building blocks it needs, while still putting the same demands on it. Instead of getting stronger and better, there is increased fatigue and risk for injury.

The physical problems caused by overtraining can negatively affect self-confidence. Exhaustion can increase feelings of depression and loss of motivation to compete.

Your gut affects your mental state in how a person feels physically but the reverse is also true. The mental state affects the gut and gut health. The physical demands of athletic performance may cause a stress response that can adversely affect the gut bacteria and cause leaky gut syndrome.