The intestine is responsible for absorption of nutrients but also to keep large molecules and germs out of our bodies. It has been suggested that exercise may result in a "leaky gut", a condition where this barrier function is compromised. This is also potentially a cause for gastro-intestinal (GI) problems we sometimes see in athletes. Let's explore.
The intestine plays an important role in absorption but also in the prevention of infection, chronic inflammation and other problems. The intestine is essentially a tube, lined by a single layer of cells, that form the barrier between the inside of the gut and the rest of the body. This barrier is effective at absorbing nutrients, but also prevents most large molecules and germs passing from inside the bowel into the bloodstream. In some circumstances, this barrier can become less effective and "leaky". Exercise may be one of those circumstances. Whether this is a problem and whether this is sometimes a cause of reported GI problems remains a topic of investigation. Here we will investigate whether a leaky gut (scientists call this increased permeability) may be caused by heat or by a lack of oxygen (hypoxia).
The intestine is essentially a barrier effective at absorbing nutrients, but also preventing most large molecules and germs passing from inside the bowel into the bloodstream. In some circumstances, this barrier can become less effective and "leaky".
What causes a leaky gut?
Exercise has an effect on the muscles, heart and lungs but also on the gut. Exercise, can, in some cases, result in GI-symptoms such as vomiting, diarrhoea or bloating (see blogs gastro-intestinal symptoms in athletes and causes of GI problems in athletes).
A considerable amount of research has investigated how exercise affects the gut, trying to discover the underlying mechanisms behind exercise-related gastro-intestinal or GI symptoms and intestinal permeability (see also blog causes of GI problems in athletes). Two of these mechanisms are:
a reduced splanchnic blood flow (a reduction in blood flow to the gut during exercise),
an increase in core temperature.
Increased muscular activity and metabolism during exercise generate heat, which results in an increase in core temperature. Normally maintained around 37°C, core temperature can rise during exercise to 40°C. In both laboratory and human studies, this rise in core temperature has been associated with increased permeability of cells within the GI tract. An increase in permeability means that otherwise impassable molecules and bacteria contained within the GI tract can now transit into circulating blood. If these molecules and bacteria cannot be cleared at a fast enough rate, endotoxemia can occur. This is a potentially life-threatening inflammatory response associated with pathological conditions such as heat exhaustion and heat stroke.