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Why Isn't Your Probiotic Making You Happier?

Manipulating the gut microbiome is possible, but not always easy.

Key points

  • Do probiotics make your gut microbiome healthier? In fact, no one knows.
  • Scientists have yet to define what a healthy human microbiome should look like
  • People’s confidence about the benefits of probiotics is not matched by the currently available evidence.
  • Probiotics are ubiquitous, expensive, and generally ineffective with regard to their ability to reduce symptoms of depression.

Probiotics are popular with consumers and marketing executives. They can be found in a vast array of products in grocery stores and pharmacies. Are they helpful? People praise their effectiveness on the internet. True believers in probiotics claim that products containing them make their guts healthier. Are they correct? Do probiotics make your gut microbiome healthier?

In fact, no one knows. The gut microbiome is awesomely complex; its components remain a near-total mystery. We are told that it is important to cultivate a healthy microbiome, however, scientists have yet to define what a healthy human microbiome should look like. Thus, how are we to know when we have achieved microbiome victory?

What is known: the typical human gut contains many different types of bacteria that are constantly changing in response to the contents of the diet. This fact appears to confirm that it is possible to alter the microbiome. Unfortunately, no one has figured out how to effectively and safely manipulate the microbiome. The challenge is because there are many other factors that influence the microbiome, such as who your parents are, who you live with, your age, where you live, and how much you exercise. Overall, the contents of the diet are likely the most important determinant of gut health.

Study after study has confirmed one very important fact: people’s confidence about the benefits of probiotics is not matched by the currently available evidence. One major problem is that probiotic means many different things to different people. All probiotics are not the same. Is one strain of Lactobacillus better than another? No one knows. Companies sometimes conduct their own “studies” and report only the positive results, if there are any. One commercially funded study examined whether a tablet containing 1 billion Bifidobacterium lactis could benefit people who suffer from constipation. Sadly, none of the subjects in this study experienced faster movement of food through their colon. Why? Did they take too few bacteria? Would more bacteria have produced better effects? Is 1 billion bacteria a lot? What about 10 billion?

Consider this: the gut contains about 500,000,000,000,000 bacteria. Thus, consuming a tablet containing 1 billion Bifido bugs is about as influential as squirting an eyedropper of water into the ocean. Essentially, your gut bugs never notice the small group of newcomers and they are never allowed to establish a home in the gut. All of your gut real estate is already taken.

Probiotics and the Brain

Your brain cares about what’s in your gut. Gut microbiota influence brain functions and behavior. Many recent studies have considered the role of the microbiome in depression. One recent large randomized double-blind controlled trial evaluated the effect of probiotic treatment in depressed individuals. Clinical symptoms, as well as gut microbiome, were analyzed at the beginning of the study, after one and after four weeks. The main finding was that the probiotic intervention only improved the microbial diversity profile; it had no effect on any clinical outcome measures. The probiotics had no effect on their symptoms of depression.

Another recent study examined the effects of psychobiotics on depression symptoms. Psychobiotics is a newly invented term that refers to probiotics that may confer mental health benefits through interactions with gut bacteria. Although the authors reported a statistically significant, but very small, benefit with psychobiotics, the authors could not specify any specific strain, strains, dosage, or duration of treatment that would reliably improve mood.

Sometimes, probiotics can produce unwanted negative side effects. One small study published a few years ago in the journal ​Clinical and Translational Gastroenterology reported a potential connection between brain fogginess and probiotic use due to increased bacterial overgrowth and lactic acidosis.

Manipulating our gut biome is possible, not easy, and sometimes not helpful. Furthermore, we are still quite ignorant about the best way to achieve a healthy gut microbiome. Bottom Line: Probiotics are ubiquitous, expensive, and generally ineffective with regard to their ability to reduce symptoms of depression.

One thing is certain, the probiotic industry is large and lucrative; don’t depend on the FDA to help out. You are one your own. Good eating.

References

Wenk GL (2019) Your Brain on Food, 3rd Ed. (Oxford University Press)

Misera A et al (2021) Effect of Psychobiotics on Psychometric Tests and Inflammatory Markers in Major Depressive Disorder: Meta-Analysis of Randomized Controlled Trials with Meta-Regression. PHARMACEUTICALS 14 (10).

Reininghaus EZ et al (2020) PROVIT: Supplementary Probiotic Treatment and Vitamin B7 in Depression-A Randomized Controlled Trial. NUTRIENTS 12 (11)

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