The human body fosters over 2100 different species of bacteria and between 10-100 trillion individual bacterial cells. [R] It is unsurprising with so many bacteria in our body that they have a strong impact on our physiology. An unhealthy gut microbiota can trigger immune disorders, infection and inflammation, among other things. [R]

Optimising one’s gut, therefore, via probiotics, is not only of great benefit to mental and physical health but could also be a tool to combat a variety of diseases and disorders. [R] With so many different gut bacteria, however, it is difficult to know where to start so I have broken down which bacterial strains are best for what health concerns…

Metabolism (Weight Loss, Diabetes, Heart Disease)

• Lactobacillus rhamnosus
• Lactobacillus acidophillus
• Lactobacillus casei

The relationship between the gut and metabolism, as well as metabolic disorders, cannot be understated. More and more crazy stories have come into the news demonstrating this. For example, you may have heard of the women who received a faecal microbiota transplant (poo transplant to transfer healthy bacteria) for Clostridium difficile infection from her overweight daughter, who over a period of sixteen months post-transplant gained 34lbs despite extensive exercise and dieting efforts. This case suggests that one’s gut microbiome could strongly predict their body type. [R]

In line with this idea, early life disturbance in normal gut microbiota development, either through antibiotic exposure or being delivered by caesarean section, have been associated with becoming obese later in life and having higher numbers of Firmicutes bacteria in the gut has been shown to increase the likelihood of obesity and heart disease. [R1] [R2] [R3] [R4] [R5]

As well as obesity, the gut microbiota can also lower type 2 diabetes risk. It seems as if beneficial butyrate-producing bacteria seems to have the most potent impact in this regard. [R1] [R2] In mouse studies, the probiotics Clostridium butyricum and Lactobacillus casei improved diabetes symptoms partially via increasing the number of butyrate-producing bacteria and decreasing Firmicutes bacteria. [R1] [R2]

It is also worth noting that butyrate produced by gut bacteria could theoretically have anti-cancer effects and that various probiotics have the ability to lower LDL cholesterol and elevate HDL cholesterol. [R1] [R2] [R3]

Brain (Emotional Regulation, Depression, Anxiety)

• Lactobacillus rhamnosus
• Bifidobacterium bifidium
• Bifidobacterium longum

The bacteria in your gut affect your brain via multiple pathways. They produce nutrients, which can be used by your brain for fuel, such as butyrate, and they can reduce or alter systemic inflammation, which is known to have a profound impact on mental health. Furthermore, many bacterial species have the ability to produce a variety of well-known neurotransmitters (dopamine, serotonin, acetylcholine, GABA, etc). Some of the neurotransmitters may reach the brain but we know for certain that these stimulate the vagus nerve, which is also known to have a variety of mental benefits (see more here). [R1] [R2]

When trilaled, a probiotic mixture of Bifidobacterium bifidum, Bifidobacterium lactis, Lactobacillus acidophilus, Lactobacillus brevis, Lactobacillus casei, Lactobacillus salivarius, and Lactococcus lactis was shown to reduce non-depressed individual’s propensity for negative mental states, meaning that probiotics could be useful in depression prevention. [R]

Indeed, Bifidobacterium and Lactobacillus strains are known to have a particularly strong effect upon decreasing anxiety and fermented food, a rich probiotic source, have also been shown to reduce social anxiety in anxiety-prone individuals. [R1] [R2]

With regard to specific strains, the Bifidobacterium infantis bacteria can reduce the stress response, [R] Lactobacillus helveticus combined with Bifidobacterium longum has been shown to decrease anxiety and urinary stress hormone in both mice and humans, [R] Bifidobacterium bifidium reduced reported stress in undergraduate students, [R] Lactobacillus rhamnosus is known to aid in many aspects of emotional regulation [R] and Lactobacillus acidophilus upregulates cannabinoid (CB1) receptors and mu-opioid receptor, which has been shown to reduce pain and could hypothetically improve mood also. [R] Furthermore, in a rat study, Bifidobacterium longum was shown to be as effective as citalopram, an SSRI, in treating a particular model of depression. [R]

The gut microbiome is also known to impact cognitive processes, especially bacteria of the Bifidobacteria strain, and a western (high saturated fat, high sugar) diet has been shown to impair cognition for this very reason. [R1] [R2]

In contrast to probiotics, a huge study of over one million people showed that a single course of antibiotics significantly increased people’s risk of depression by between 15-35% depending upon the antibiotic, while an additional course increased depression risk by between 35-65%. Similar results were seen when comparing antibiotic use to cases of anxiety issues. [R]

Also worth noting is that the clostridium bacteria has been linked to autism spectrum disorder. [R]

Immune System

• Lactobacillus acidophillus
• Bifidobacterium bifidium
• Bifidobacterium longum

The gut microbiome plays an important role in immune system function right from birth. [R] Good gut bacteria compete with pathogenic gut bacteria for adherence to the intestinal wall and produces bacteriocides, killing harmful pathogens. [R]

Digestion (IBS, Constipation, IBD, Bloating and more)

• Lactobacillus casei
• Lactobacillus acidophillus
• Faecalibacterium prausnitzii

Gut bacteria prevent intestinal inflammation by lubricating the gut wall. [R] This is atop the effects of gut symbiosis (as opposed to dysbiosis) reducing inflammation generally. [R]

One particular bacteria species known for its digestive effects is Faecalibacterium prausnitzii. Faecalibacterium prausnitzii is an anti-inflammatory butyrate producer has been suggested to prevent and counteract various inflammatory bowel diseases. [R1] [R2] The gut microbiota also seems to affect digestion and intestinal inflammation via stimulation of vagus nerve. [R]

Furthermore, in addition to gut inflammatory issues, probiotics promote intestinal epithelial cell survival, enhance barrier function, and stimulate protective responses from intestinal epithelial cells and could treat stomach ulcers, stomach pain, diarrhoea, constipation, bloating, excessive gas and heartburn. [R1] [R2] [R3] [R4]

Skin (Acne, Ageing, General Health)

• Streptococcus salivarius
• Streptococcus thermophiles

Acne development is usually dependant upon skin colonisation by the bacterium Propionibacterium acnes. Good gut bacteria are capable of suppressing the growth of Propionibacterium acnes via producing antibacterial proteins and bacteriocides. [R]

Streptococcus thermophiles and Streptococcus salivarius have been shown to be particularly potent in this respect. Both oral and topical (cream) applications of these bacteria have been tested with success. [R]

Gut bacteria, such as Streptococcus salivarius, are also beneficial in acne treatment and for skin health generally by modulating inflammation within skin cells. This effect also grants probiotics beneficial effects upon reducing the symptoms of skin ageing and possibly other dermatological disorders. [R]

Liver (Fatty Liver, Liver Enzymes)

• Bifidobacterium longum
• Lactobacillus fermentum
• Lactobacillus casei

A common symptom of fatty liver disease is gut dysbiosis and gut dysbiosis increases one’s risk of fatty liver disease suggesting that a liver-gut axis exists. [R1] [R2] Those with such liver issues have higher levels of Firmicutes bacteria present in the gut, something also seen in obese individuals. [R]

Bifidobacterium longum, in addition to prebiotics and lifestyle modifications, improved fatty liver disease in one study, along with reducing the liver enzyme AST, liver inflammation and liver insulin resistance. [R]

Gut bacteria also affect levels of glutathione in the body, which is known to powerfully, in turn, affect liver function. [R]

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