The microbiota of the human body contain 10-100 trillion microbial cells, some of which assist in maintaining good health,1 and probiotics can support this process.2 While probiotics are often defined as live microorganisms that provide health benefits to the person taking them, some scientists believe the term should be restricted to microorganisms that have been tested and proven effective in doing so.3
There are multiple types of probiotics identified by their genus, species, and strain (e.g., Lactobacillus acidophilus ABC). Getting probiotics through food or supplements can be equally effective as long as people are getting the correct probiotic strain at an effective dose.4 Some yogurts, fermented milk products, and other foods may contain probiotics.5
It’s commonly believed that probiotics are effective because they alter the gut microbiota; however, this is not always true. In fact, while they do grow, metabolize, and interact with resident microbes, probiotics rarely become a permanent part of the gut microbiota.6
Prebiotics are types of fiber that cannot be digested by the human body but can be digested by the beneficial microbes living in the colon and elsewhere.7 It is recommended that people get at least 5 grams of prebiotics daily to maintain optimal gut health.8
Sources of prebiotics include bananas, onions, garlic, Jerusalem artichokes, and chicory root.1 People can also get prebiotics by consuming foods like yogurt, bread, or drinks that contain galacto-oligosaccharides, fructo-oligosaccharides, oligofructose, chicory fiber, or inulin.9
Numerous studies have uncovered the existence of the gut-brain axis, a pathway involving the neural, endocrine, and immune systems that allows two-way communication between the central nervous system (CNS) and the enteric nervous system (ENS).10-12
The central nervous system is made up of the brain and spinal cord, while the ENS contains about the same amount of neurons as the spinal cord and also incorporates hormones and other molecules like neuropeptides and cytokines. The ENS controls the function of the gastrointestinal tract.12
The gut-brain axis keeps track of gut functions and mediates the effects of hunger, stress, and emotions, the latter two of which can influence the physiology of the gut.12 It is also believed to be influenced by intestinal microbiota, since research has shown there are various mechanisms by which they can produce neurotransmitter precursors that reach the brain and affect several processes that influence behavior.10,11
Although it’s not yet clear exactly what molecular mechanisms are involved in communication between the gut microbiota and the brain, the link is believed to involve immune signals and the vagus nerve. Gut microbiota-produced cellular components like lipopolysaccharide (LPS), peptidoglycan, and flagellin, are believed to be distinguished by pattern-recognition receptors (PRRs) on epithelial and immune cells, and this produces CNS transmitters that include cytokines, hormones, and other molecular signals.10
The composition and activity of the gut microbiota can be affected by things like host physiology and immunology, as well as diet, antibiotic usage, and enteric infection. This interaction between host and microbes can result in impairment of neuroimmune functions, as well as gastrointestinal and metabolic disorders.12
The discovery of the gut-brain axis has drawn much attention to the use of bacteria as therapeutics.10 Recent research has illustrated the significance of the gut microbiota in the development of the brain and its related systems, and it has been associated with conditions like schizophrenia, autism, and depressive and anxiety disorders. Microorganisms in the gut can produce and deliver neuroactive substances that act on the gut-brain axis, such as serotonin and gamma-aminobutyric acid.13
Probiotic bacteria have been used in animal studies and human clinical trials to improve gastrointestinal and psychological symptoms.12 Some researchers have coined the term “psychobiotics” to describe probiotics that showed positive psychiatric effects when ingested in the correct quantities, as well as prebiotics that support such bacteria.14
Animal studies have indicated that using probiotics to change the microbial environment of the gut could help to improve mood and cognitive functions. Studies involving probiotic supplementation in rats resulted in an improvement in spatial memory and problem-solving skills, as well as beneficial effects on anxiety and depression.11
In another animal study, mice that lacked indigenous bacteria due to being raised in a sterile environment showed abnormal responses to stress compared to a control group. Those exaggerated reactions were reversed when the germ-free mice received bacterial recolonization through probiotic administration.14
Some small-scale human studies have been done on the effect of probiotics on brain health.11 One study showed reduced cognitive reactivity to sad mood after four weeks on multispecies probiotics.15 Another study demonstrated an improvement in sleep quality in students taking probiotics for 11 weeks during a period of increased stress.16 A third study found improvements in sad mood, anger, and fatigue in healthy individuals taking probiotics.11
In a study of 30 patients, those given a psychobiotic oral suspension for three weeks reported decreased anxiety.17 And in a separate trial, patients with chronic fatigue syndrome experienced a reduction in anxiety symptoms after two months of probiotic use.18
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Rejuvenation Therapeutics
* These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.
