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Diet therapy

The gut-brain axis is important to sporting performance

Do you ever suffer from” runners diarrhoea”, bouts of anxiety, fatigue, abdominal pain or gas when facing sporting competition?

It is perfectly normal to experience feelings of stress under these circumstances however when it starts to interfere with your athletic performance and goals it may be important to get some professional help.

Gaining an understanding of how the gut and brain are linked may be a helpful place to start.

What is the role of the gut and brain to performance?

To perform well as an athlete you require good mental and physical health. Your brain is an organ that requires oxygen, glucose and stimulation in order for you to plan well and think tactically, particularly while training and competing.

The gut is essential also to your performance as it breaks down food and fluids and distributes energy and nutrients to supply your working muscles.

The synergy between these two systems is referred to as the gut-brain axis.

How do these systems work together?

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. So if 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 (e.g.blood glucose) the body must draw from its stores (muscle and liver glycogen). If the event concerned is a long one e.g. a triathlon or marathon then your 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 rise

Cortisol is the hormone that increases with stress causing insulin resistance and hyperglycaemia (a high blood sugar). Persistently high blood glucose levels are associated with diabetes, weight gain and heart disease. For more information read Lea’s article “Is sleep making us fat“? Low cortisol levels can be just as bad as hypoglycaemia (a low blood sugar)for an athlete as it causes fatigue, dizziness and irritability.

Sleep deprivation, particularly a lack of the more restful deep NREM (non rapid eye movement) sleep, is also associated with higher cortisol levels and disturbed appetite. For more information read Lea’s article on Sleep deprivation affects nutritional well-being.

Gut motility

As stress levels rise the gut produces peptides that increase gut motility. This can cause diarrhoea  and altered bowel habit and over time lead to gut-brain axis disorders such as Irritable Bowel Syndrome (IBS)and Inflammatory Bowel Disease (IBD).

What can athletes do to improve gut and brain function?

Talk to us as we are Sports Dietitian’s about the nutritional needs of your sport and arrange to have a full nutritional assessment of your diet. We can help you to:

  • Check you intake of energy from protein, fat and carbohydrate to suit your baseline needs as well as your higher energy needs for training and competition.
  • Ensure your intake of vitamins and minerals, in particular, the oxygen carrying nutrients, is sufficient to meet your personal needs. In most cases dietary supplements are not required. Read Lea’s article on Brain foods for more information
  • Estimate your fluid requirements along with sweat loss testing as this will help you to recognise how fluid intake and needs vary according to climate, terrain, season and practicality. Low fluid levels can increase fatigue and reduce performance.
  • Get extra assistance if you experience alterations in bowel habit with exercise such as diarrhoea, bloating, abdominal pain and gas as  you may be suffering  from IBS or IBD. As your dietitian we can liaise with your doctor to arrange blood tests and supply practical information on dietary change if required. E.g a Gluten or Dairy free diet or the implementation of a FODMAP diet. A FODMAP diet is an acronym that stands for Fermentable oligosaccharides; Disaccharides; Monosaccharides  And Polyols. This diet was developed by Dr Sue Shepherd (1) for the treatment of IBS and can be very helpful for some.
  •  Keep a detailed training diary that records food intake as well as any symptoms or changes in performance. This will prove helpful if you need to discuss race day tactics with your coach or Sports Dietitian.
  • Take steps to reduce stress by taking a regular break from training to just “chill out” and do normal activities with you friends such as listening to music, going to movies, reading a book or watching TV.

While it is perfectly normal to feel anxious on the day of an important event practicing your competition diet in training can greatly reduce stress levels on the day. It also helps to remove some of the many variables you have to worry about leaving you free to concentrate more on the tactics of your “main event”.

If you would like to learn more about Sports nutrition  and how it can you to achieve your goals then contact us now

(1) Dr Sue Shepherd -www.shepherdworks.com.au

About the author View all

Lea Stening

Lea is one of New Zealand’s leading paediatric dietitians and also specialises in Sports Nutrition. She has specialised in Paediatric Nutrition for 31 years and in 1985 was the first paediatric dietitian to enter private practice in New Zealand. Lea helps families through her private consultations, public lectures, newspaper and magazine articles as well as television and radio interviews. Read more »

View all posts by Lea Stening »


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