PT on the Net Research

The Effects of Gut Health on Mood, Mindset, and Eating Behaviors

Many clients struggle with compliance, especially as it relates to their eating habits.  To help clients shift their mindset and get back on track, trainers often turn to coaching techniques, accountability models, or positive self-talk.  While these can certainly help, client non-compliance and mindset may be, in part, due to physiological reasons.  In this article, we will consider the role of gut bacteria and nutrition in helping clients improve their mindset. 

Learning Objectives:

  1. Understand why client non-compliance may be partly due to physiological reasons related to gut health.
  2. Identify factors that influence the population of gut bacteria.
  3. Recognize the effects of both beneficial and pathogenic bacteria on the mind.
  4. Identify interventions that personal trainers can use with clients to help them improve gut health.

Many clients struggle with healthy eating, even those that are very disciplined and motivated.  They sign up for training and are ready to change their eating habits.  They stock the kitchen with healthy foods and buy recipe books.  The first couple of days are a breeze.  They have energy and feel great.  By the third or fourth day, progress drastically changes.  Cravings go through the roof and energy levels plummet.  Comfort foods are, well, just too tempting, and the ability to control portions seems impossible.  They claim, “This happens every time I try to change my diet.  I have no willpower.”  Blaming themselves continues to adversely affect confidence, motivation, and mood. 

break the cycleAt this point, clients may want to give up, fearing they will never be able to change their bad habits.  Those that persevere may want to understand their cycle of self-sabotage and how to develop better self-control.  Creating and adhering to new habits is definitely something that requires consistency and practice, but the root cause of the problem may not lie in the brain, the subconscious, or even in negative self-talk.  It may lie in the health of the gut and the bacteria that inhabit it.

Gut Bacteria and the Gut-Brain Axis

The gut and the brain are in constant communication.  The gut communicates to the brain in several ways, but for the purpose of this article, we will focus on the communication that takes place between the gut bacteria and the brain.

Populations of bacteria (collectively known as microbiota) start inhabiting the gut during the birthing process and continue to develop and change through interactions with the environment throughout the individual’s lifespan.  These populations are influenced by (Marques et al., 2010):

Factors that are starred (*) have been shown to improve the diversity and populations of beneficial bacteria.

Communication Gone Awry

Some strains of bacteria do not work in harmony with their host.  Others cause harm to the host.  Through chemical messaging to the brain, they have the ability to manipulate both the eating behavior and mood of the person they inhabit.  It is proposed that this happens through the following mechanisms (Alcock, Maley, & Akipis, 2014):

In other words, microbes drive clients to consume foods that best feed them, even if those foods are unhealthy.  When these foods are eliminated from the diet, microbes release toxins, causing that dysphoric feeling.  If clients give in to the cravings and consume the food, microbes get the fuel they need.  As a reward for feeding them, they release chemicals that act on the pleasure centers of the brain and make clients feel good.

This feedback loop actually encourages clients to continue making unhealthy food choices.  If they feel ill while following a healthy eating plan but feel better once they have indulged in their favorite treat, who can blame them for continuing to deviate from their plan? 

One example of this is the presence of Helicobacter pylori.  People inhabited by this bacteria are more likely to experience mood disorders, which may be a result of inflammation in the gut (Holtmann, 2014).  H. pylori may also influence eating behavior and drive people to consume more food, which hinders their efforts to lose weight.

Stress Compounds the Issue

If the chemical messages from the bad bacteria aren’t enough for clients to have to overcome, stress adds fuel to the fire.  Many studies have demonstrated that psychological stress negatively affects beneficial gut bacteria.  A study testing the stool samples of college students found the samples contained fewer lactobacilli during exam week than earlier in the semester (Knowles, 2008).  Lutgendorff, Akkermans, & Soderholm (2008) reported that psychological stress decreases lactobacilli populations and allows pathogenic forms of E. coli to flourish.

Other studies have demonstrated the same results: stress reduces the diversity and populations of beneficial gut bacteria and allows harmful bacteria to proliferate.

Consider the busy lives of most people today. They are juggling their job, family, and social needs. Add the stress of changing their daily habits and lifestyle, and the recipe for an altered gut microbiome and a challenged mindset is complete.

Our Little Helpers

Not all bacterial strains wreak havoc on the mind and body.  In fact, some are essential for human health.  They help digest food and absorb nutrients, maintain a healthy body weight, and balance mood, among others.  The strains that have a positive effect on mood are known as psychobiotics, and include Lactobacillus helveticus, Bifidobacterium longum, and Bifidobacterium infantis.

Healthy subjects administered a probiotic formulation of Lactobacillus helveticus and Bifidobacterium longum for 30 days reported less psychological distress (Messaoudi et al., 2011).  Rats given the same formulation for two weeks exhibited less anxiety-like behavior.  In another study, Bifidobacterium infantis helped alleviate depressive symptoms (Dinan, Stanton, & Cryan, 2013). 

Breaking the Vicious Cycle

While there is more to mindset than the health of the gut, it is clear that the gut plays a role in mood, mindset, and behavior.  Researchers are still investigating the best ways to restore the microbiome of the gut.  However, several helpful interventions have been identified that are within the scope of a personal trainer. 

Improving client compliance does require accountability models and coaching techniques.  However, given that the bacteria in the gut communicate with and affect the brain, the impact of gut health cannot be discounted.  It affects clients’ mood, mindset, and eating behavior.  By improving the health of the gut and decreasing stress, clients may experience fewer mood fluctuations.  They may be more compliant in eating healthy foods as their cravings decrease.  Most of all, clients may feel more empowered, knowing they can take concrete steps to improve their gut health and finally let go of their long-term struggle with eating healthy.


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Dinan, T. G., & Cryan, J. F. (2013). Melancholic microbes: a link between gut microbiota and depression?. Neurogastroenterology & Motility, 25(9), 713-719.

Dinan, T. G., Stanton, C., & Cryan, J. F. (2013). Psychobiotics: a novel class of psychotropic. Biological psychiatry, 74(10), 720-726.

Kim, D. Y., & Camilleri, M. (2000). Serotonin: a mediator of the brain–gut connection. The American journal of gastroenterology, 95(10), 2698-2709.

Knowles, S. R., Nelson, E. A., & Palombo, E. A. (2008). Investigating the role of perceived stress on bacterial flora activity and salivary cortisol secretion: a possible mechanism underlying susceptibility to illness. Biological psychology,77(2), 132-137.

Holtmann, G., & Talley, N. J. (2014). The stomach–brain axis. Best Practice & Research Clinical Gastroenterology, 28(6), 967-979.

Lutgendorff, F., Akkermans, L., & Soderholm, J. D. (2008). The role of microbiota and probiotics in stress-induced gastrointestinal damage. Current molecular medicine, 8(4), 282-298.

Marques, T. M., Wall, R., Ross, R. P., Fitzgerald, G. F., Ryan, C. A., & Stanton, C. (2010). Programming infant gut microbiota: influence of dietary and environmental factors. Current opinion in biotechnology, 21(2), 149-156.

Messaoudi, M., Lalonde, R., Violle, N., Javelot, H., Desor, D., Nejdi, A., ... & Cazaubiel, J. M. (2011). Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects. British Journal of Nutrition, 105(05), 755-764.

Petra, A. I., Panagiotidou, S., Hatziagelaki, E., Stewart, J. M., Conti, P., & Theoharides, T. C. (2015). Gut-microbiota-brain axis and its effect on neuropsychiatric disorders with suspected immune dysregulation. Clinical Therapeutics, 37(5), 984-995. doi:

University of California, San Francisco (UCSF). (2014, August 15). Do gut bacteria rule our minds? In an ecosystem within us, microbes evolved to sway food choices. ScienceDaily. Retrieved from