Gut health for young athletes

Do you have a budding athlete? You may be surprised to know how important their gut health can be to their overall performance.

A healthy, happy gut is essential to physical and mental performance. Yet often athletes may suffer from reflux, fatigue, constipation, abdominal pain, and bloating. Others might notice how nerves, before an event, can affect their appetite, sleep and, if competing in endurance or running events, they might experience “runner’s trots” (i.e. exercise-associated gastrointestinal symptoms).

What is the link between the brain and how the gut reacts under stress, and is it possible to change the environment within the gut in order to settle it down? Let’s take a look at some main areas of gut health that may affect young athletes.

The gut microbiome

There are trillions of microorganisms (mainly bacteria) living in our body and most can be found in the large intestine. These organisms outnumber healthy body cells 10:1, and these thrive in different varieties/strains. Just like a fingerprint, their combinations are unique to each one of us. From birth until the age of 3-5 years, we are assembling our own gut microbiota into a complex ecosystem. Our age, birth delivery route (vaginal versus caesarean section), whether we were breast- or bottle-fed, our antibiotic use, whether we live with pets or farm animals, and our diet are just some of the factors that influence this microbiota growth.

These microbiota are essential for processing our foods and help to shape our immune system.

Studies suggest that changes in a person’s microbiome correlate with certain disease states and that by manipulating the growth of these bacteria, and the dietary foods consumed, it might be possible to treat some diseases.

Exercise has also been found to have a positive influence on the diversity and abundance of health-promoting bacterial species that are found in individuals who exercise, compared with those who have a more sedentary lifestyle.

Research is now underway to look at the effects on microbiota growth of different types of exercise (for example, endurance versus bodybuilding), different body compositions, different levels of proficiency (that is, amateur versus elite), and dietary combinations (levels and types of fat, dietary fibre, protein, and carbohydrate) during exercise and recovery, in the hope of limiting those metabolites that might worsen the consequences of exercise stress.

Remembering that everyone’s combination of microbiota may be different, this research is not for the faint-hearted. While there are no firm recommendations yet that might help developing athletes to improve their performance in specific sports, interest has been growing into the use of pre- and probiotics to improve overall gut health.

What are pre- and probiotics?

Specific strains of health-promoting bacteria are known as probiotics. The most common ones are Saccharomyces, Bifidobacterium, and Lactobacillus. These can be found in food such as yoghurt and some fermented foods, like unpasteurised sauerkraut (fermented cabbage), kombucha (fermented tea), miso (fermented soybean paste), and kimchi (a Korean fermented cabbage dish).

In order to keep the gut healthy, these bacteria need to survive transit through the gut, resist gastric acids and bile salts in order to reach the large intestine intact, where they may attach themselves to the cells that line the intestine. Here it is thought that probiotics may act to strengthen our immune system, help us to absorb nutrients, produce neurotransmitters such as serotonin (the “happy hormone”) and improve bowel regularity.

Prebiotics, on the other hand, are non-digestible carbohydrate foods that feed these health-promoting bacteria. While not all fibre-containing foods have a prebiotic effect, cashews, almonds, dried fruit, bananas, cabbage, onion, beetroot, barley, wheat bran, oats, lentils, chickpeas, soybeans, baked beans, and sweetcorn are examples of those that do.

Some Tots to Teens Takeaways…

  • Exercise has a positive effect on gut health – athletes have more diverse gut bacteria than people who don’t move as much.
  • When kids are stressed, their gut gets a bit stressed too, causing diarrhoea and discomfort.
  • When in doubt, go back to basics and check that your child’s diet is balanced and that they are getting the nutrients they need, particularly if they are exercising a lot.

The gut-brain axis

To understand how stress and anxiety can upset the gut, we need to look at what links the gut and brain function to physical performance.

Around 90% of the brain’s activity passes through the lower 60% of the brain stem, into the vagus nerve, which activates the digestive tract. Basically, there exists a feedback loop of activity between the two systems of the brain and gut, known as the gut-brain axis (GBA).

The role of the GBA is to monitor gut functions as well as to link the emotional and cognitive centres of the brain with the intestinal functions. So if, for example, the brain slows due to changes in glucose, oxygen supply, or mood, then the gut activity is also reduced, affecting the following systems:

Energy levels

As gut activity slows, the release of hydrochloric acid in the stomach is reduced, along with the secretion of enzymes from the pancreas and bile from the gall bladder. These secretions are important for the breakdown of fat and carbohydrate for energy and protein for tissue repair. Without a good supply of circulating energy (such as blood glucose), the body must draw from its stores (muscle and liver glycogen). If this occurs when a long event is being undertaken, like a triathlon or marathon, then the athlete’s level of endurance may be compromised.


As intestinal activity slows down, so too does the immune system, reducing intestinal blood flow. This can lead to a low-grade inflammation of the gut and brain, thereby reducing nerve conductivity.

Mental functions

Within the brain, a lack of nerve excitation leads to lowering of mood, memory and judgement, and feelings of depression, anxiety and stress can increase.

Stress levels

Cortisol is the hormone that increases with stress, causing insulin resistance and hyperglycaemia (a high blood sugar). Persistently high blood glucose levels can cause deterioration in health, diabetes, weight gain and heart disease over time. Low cortisol levels can be just as bad, with hypoglycaemia (a low blood sugar) leaving an athlete feeling fatigued, dizzy, and irritable. Sleep deprivation, particularly a lack of the more restful, deep NREM (nonrapid eye movement) sleep, is also associated with higher cortisol levels and disturbed appetite.

Gut motility

As stress levels rise, the gut produces peptides that increase gut motility. This may cause diarrhoea and altered bowel habit and over time can lead to such disorders as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD).

What can athletes do to improve gut and brain function?

  • Go back to basics and check that their energy from protein, fat and carbohydrate, intake of vitamins and minerals suits their baseline needs, as well as their higher energy needs for training and competition. In most cases, nutritional supplements are not required.
  • Normally avoid foods that are low in fibre but rich in refined sugars, saturated fat, and alcohol, as these reduce the number of bacteria associated with good health. This can lead to increased inflammation and stress and affects the central nerve system, causing changes in mood, behaviour, impaired memory, attention, and executive functions (planning, reasoning and problem-solving).
  • Estimate fluid requirements, along with sweat loss testing, because fluid intake affects gut motility. Low fluid levels can increase fatigue and reduce performance. If feeling bloated, by replacing gaseous drinks (including mineral water) with tap water, athletes should notice a drop in the incidence of farting and burping.
  • Get extra assistance if they experience alterations in bowel habit with exercise. Working together, a doctor and sports dietitian can arrange blood tests and supply practical information on dietary change if required – for example, a gluten- or dairy-free diet or the implementation of a FODMAP diet.
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