“Rather than lactate being a waste product resulting from intense exercise,” Newton explains, “it can actually be recycled by the gut microbiome into something helpful. But the system needs to be balanced; if lactate levels increase too much [for example, during high-intensity exercise], this can lower the pH of the gut excessively, which is not a good thing.”
High-intensity exercise over a long duration can cause gut dysbiosis (an imbalance of microorganisms in the gut microbiome) and inflammation. “Prolonged, high-intensity endurance exercise is particularly problematic, especially long-distance running,” says Newton. “Hot conditions make things worse, as does dehydration and inadequate fuelling.”
But what happens if you are forced to suddenly stop training – due to injury, for example? “The gut microbiome tends to shift back towards its baseline, its pre-training state,” Newton replies.
“Studies suggest that the microbial diversity you have built up will gradually decline. However, when athletes take a break from training, that decline is much slower because they have built up more microbial diversity and greater resilience.”
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Marathon or triathlon training
Irregular or long-lasting training has a negative impact on the microbiome, and there is extensive evidence that long-distance running and other endurance events can cause gastrointestinal distress.
During longer sessions, blood flow is diverted away from the digestive system, as it is needed by the muscles. This reduces oxygen supply to the gut, which can cause intestinal permeability, also known as “leaky gut”. The intestinal lining becomes damaged, allowing undigested food particles, toxins and bacteria to leak into the bloodstream.
“With less blood flow in your gut, you are not going to digest things as well,” says Newton. “Your stomach does not empty as quickly and your gut motility may be impaired. That is why long-distance runners sometimes get diarrhoea or so-called ‘runner’s trots’. The pounding action of running can irritate the intestines, which is why people experience more gastrointestinal symptoms with running than they do with cycling or swimming.
“If you are thinking of running a marathon, it is important to find ways to manage the stress on your gut,” she says. “Running long distances, especially in hot conditions, is likely to cause intestinal permeability. But if you stay hydrated and make sure your nutrition is right, those risks will be minimised.”
Eating the correct foods and allowing adequate time for recovery are key. “If you are sleeping well”, Newton says, “this will allow your gut to recover. I worked with one client who was getting up ridiculously early to fit in training sessions. They were sacrificing their sleep to do that, which had a knock-on effect on their gut health.”
