Mood issues affect many people

Over 20% of the US population will be affected by a serious mood issue (anxiety, depression, etc.) at some point in their lives, making finding necessary treatment options a top priority.^1,2 In addition to those suffering from serious mood issues, many others experience subtle mood problems – mood states that are not classified as a medical issue but can make some days more unpleasant than they need to be. The concern with subtle mood issues is that if these feelings persist for a while, there’s a risk that they could turn into more serious problems, especially if a stressful life event occurs.³

The gut-brain-axis

Medication is often not the preferred treatment for those experiencing subtle mood issues, leading many to look for natural health strategies that can help support a more positive mood. According to the research, several dietary and lifestyle choices can alter the gastrointestinal tract in a way that greatly impacts brain activity and mood via the gut-brain-axis – a biochemical signaling system that connects your gut and your brain.^3,4 In this article, we will focus on how the bacteria and other microorganisms in your digestive tract—collectively known as your gut microbiota—can affect mood, and whether the intake of beneficial bacteria (probiotics) can support a healthier, more positive mood.

Gut bacteria communicate with the brain via chemical signals

The bacteria in our gut can influence brain activity through many different routes. For example, chemical “signals” produced by gut bacteria can be picked up by the nerves in the gastrointestinal tract and get relayed to the brain.⁵ This is important from a survival standpoint, as the brain needs to be able to recognize pathogens so that it can trigger the proper immune responses to eliminate unwanted bugs.

Mood problems may arise when gut bacteria become imbalanced

In many of today’s developed societies, the treatment of acute infections has largely been replaced by the treatment of chronic health conditions (such as mood issues) that may be related to unfavorable changes in gut bacteria.⁶ Indeed, characteristics of our modern lifestyle (high stress levels, poor dietary choices, and exposure to a variety of environmental pollutants) can lead to an oversupply of “bad bacteria” and lesser amounts of “good bacteria” in the gut.^7,8 This has caused some to question whether today’s modern lifestyle may be leading to an imbalance of gut bacteria, and thereby contributing to poor mood.⁹

To help answer this question, we can look at how our body deals with irritants. When fighting off an infection or dealing with an injury, the human body is wired to direct its energies towards rest and recovery. For instance, we’ve all experienced how a cold or flu can make us feel exhausted, emotional, irritable, and generally lousy – which is why these feelings are commonly referred to as “sickness behavior.”¹⁰ Scientists now have reason to believe that sickness behavior and mood issues arise when our gut bacteria become imbalanced.^4,10 Evidence in support of this concept comes from studies showing that those with unhealthy blood sugar levels have unfavorable changes in gut bacteria and more frequent problems with low mood.^11,12

Short-chain fatty acids produced by the gut microbiota support the integrity of the brain-barrier

Another way that the gut microbiota may influence mood is through the production of an important energy source for the brain, short-chain fatty acids (SCFAs).¹³ Research has found that those with low mood issues have lesser amounts of the bacteria responsible for the production of SCFAs.¹⁴ One of the similarities between the brain and the gut is that they both have a protective barrier that relies on SCFAs to function optimally and to limit the passage of unwanted chemicals.^15,16 This means that if the brain doesn’t receive adequate SCFAs from the gut, the integrity of the brain-barrier may become compromised – letting unwanted chemicals to enter the brain, which may impact mood.¹⁷

Can taking probiotics help support a more positive mood?

Certain species of probiotics (live bacteria and yeasts that confer a health benefit when consumed in adequate amounts)¹⁸ have been shown to support the function of the gut barrier– a protective structure that prevents unwanted toxins, including byproducts of “bad bacteria,” from entering the blood and ending up in the brain.^19,20 When toxic bacterial byproducts become bloodborne, it causes the immune system to flare up, causing “sickness behavior” that often results in problems with focus and attention, fatigue, anxiousness, and low mood.^21,22 Indeed, many studies have shown that when healthy volunteers are injected with toxins from bad bacteria, it increases their states of anxiousness and sad mood.²¹ Considering that bacterial toxins can cause hyperactive immune responses, changes in brain chemistry, and “sickness behavior,” many researchers have designed trials to evaluate exactly how probiotics may influence immune responses and emotions.

In one such recent trial (2019), healthy subjects with moderate stress levels received a probiotic supplement or placebo for 12 weeks to assess whether probiotics would have an effect on participants’ stress levels, anxiousness, cortisol, psychological and cognitive scores, and immune system activation.²³ The results indicated that those who took probiotic supplements had significantly lower stress and cortisol levels, less anxiety, more favorable psychological and cognitive scores, and healthier immune responses than those in the placebo group. 

In another recent trial, men and women who had recently experienced a heart attack (an event linked to drastic changes in mood) were assigned to take a probiotic supplement or placebo for 12 weeks.²⁴ At the end of the trial, the probiotic group demonstrated improved mood and healthier immune responses than individuals in the placebo group.

Although recent research examining the effects of probiotics on mood is encouraging, it’s important to consider that because of the variability in probiotic species, doses used, pill technology, and drastic differences in the subjects entering the trials, it is too early to definitively say that supplementation with “probiotics” will reliably support a more positive mood.^25,26 That said, probiotics do appear to be a prudent research avenue worth investigating in support of mental health. 

Conclusion

Having an adequate supply of the “good bacteria” appears to support a healthy gut barrier – a structure that limits gut-derived toxins from getting absorbed into the blood. If lesser amounts of toxins are able to reach the blood, healthier immune responses can be expected, which may influence mood states. Although more research is needed to determine if adding probiotics to the diet promotes a positive mood, we encourage you to speak to your doctor about any gut-related issues, and whether supplemental probiotics can help.