There are ten times more bacteria in your body than your body has cells and most of these bacteria are found in your gut. Most of these bacteria are harmless and having the right composition of gut bacteria has even been linked to numerous health benefits, including weight loss, better digestion, improved immune system function, healthier skin and reduced risk of numerous diseases (1, 2). The entirety of all bacteria and other microorganisms that live in the intestine is also referred to as intestinal flora. Probiotics, which are specific types of "friendly" bacteria, have a variety of health benefits. They are often taken as a supplement and are designed to colonize your gut with bacteria that will improve your health.
After birth, the sterile human gut is immediately colonized by different types of microorganisms that come from the mother and the environment. By the age of one year, each person has developed an individual and unique bacterial profile. The intestinal flora consists of at least 1014 different bacteria belonging to at least 160 different species of bacteria from a pool of 1000 to 1150 bacteria. (3, 4). The total mass of bacteria living in the gut is between 1 and 2 kilograms (5). Surprisingly, the metabolic activity of the intestinal flora resembles that of an organ. For this reason, some scientists refer to the intestinal flora as the "forgotten organ" (16). The intestinal bacteria comprise about 30 different species of bifidobacteria, 52 species of lactobacilli and numerous other species such as Streptococcus and Enterococcus (6). The genome of the entire intestinal flora exceeds the human cell genome by a factor of at least 100 (4). The human intestinal flora is significantly involved in various metabolic, nutritional, physiological and immunological processes (7). It plays an important role in energy homeostasis and influences mood and cognitive abilities via the gut-brain axis (4). It also stimulates the immune system, prevents infestation with pathogenic microbes and bacteria and produces vitamins such as vitamin B and K (3). The intestinal flora also converts dietary fiber into short-chain fatty acids such as butyrate, propionate and acetate, which serve as food for the cells of the intestinal wall and fulfill many metabolic functions (17, 18).
These fats also stimulate the immune system and strengthen the intestinal wall. This can help prevent unwanted substances from entering the body and triggering an immune response (19, 20, 21, 22). Diet can have a profound effect on the bacterial profile of the gut flora and people in different parts of the world have different bacterial profiles (8). For example, there is an association between bacterioids and a diet rich in animal fats and proteins, while the Prevotella enterotype is associated with a high carbohydrate diet (8).
However, not all gut bacteria are friendly. Gut flora is very sensitive to diet and studies have shown that out-of-balance gut flora can be associated with numerous diseases, which can include obesity, type 2 diabetes, metabolic syndrome, heart disease, colon cancer, Alzheimer's disease and depression (9, 10, 11, 12, 13, 14)
Changes in the composition of gut flora can also increase susceptibility to infections, immune system dysfunction, inflammation, oxidative stress and insulin resistance (7).
Probiotics - and prebiotics - can help restore this balance and ensure your 'forgotten organ' is functioning optimally (15).
Probiotic bacteria are live microorganisms, also known as 'friendly' gut bacteria. These bacteria can provide potential health benefits when present or administered in adequate amounts (3).
The term 'probiotic' originally comes from the Greek and means 'for life' (7). Probiotics (especially lactic acid bacteria such as lactobacilli and bifidobacteria) have been considered beneficial since ancient times, but they first came into the spotlight in the late 19th century and early 20th century when scientists speculated that consuming yogurt containing lactobacilli could reduce toxin-producing bacteria in the gut and increase longevity (7).
Probiotic foods include yogurt, kefir, sauerkraut, tempeh and kimchi. Probiotics should not be confused with prebiotics, which are dietary fibers that serve as food for the friendly bacteria in the gut (24). There are dozens of different probiotic bacteria that have health benefits. The most common probiotic strains belong to the species Lactobacillus and Bifidobacterium, followed by the genera Streptococcus, Enterococcus, Propionibacterium, Bacillus and Escherichia. In addition, some yeast species such as S. boulardii and S. cerevisiae are also used as probiotics (23, 3).
According to some studies, probiotics can potentially improve the function of the immune system and skin function, increase resistance to allergens and reduce pathogens in the body (25). It may also have anti-inflammatory effects, help improve blood lipid levels and glucose tolerance, and lower blood pressure and BMI, although some of these benefits have not yet been clearly demonstrated (26, 27).
Interestingly, different probiotics address different conditions and health problems. For this reason, choosing the right types of probiotics is essential. Some supplements, known as broad-spectrum probiotics or multi-probiotics, combine different species in one product.
At this point, it should be mentioned that probiotic mixtures often show better effects than a single strand in clinical studies when it comes to improving the composition of the intestinal flora (6).
Prebiotics are special carbohydrates such as polysaccharides, fructans and inulin, which can have positive effects on the composition and metabolic activities of intestinal microorganisms. A diet rich in inulin and related fibers, for example, has been shown to increase the number of bifidobacteria (3).
A combination of probiotics and prebiotics is called a synbiotic when the net health benefits are synergistic (28).
A large number of studies and clinical trials point to a variety of health benefits and potential health benefits. In the following sections, we will take a brief look at the most important of these benefits and the scientific evidence.
Probiotics have been extensively studied for their effects on digestive health (31). Among other things, there is strong evidence that probiotic supplements can help cure diarrhea associated with antibiotic use (32, 33, 34). When people take antibiotics, they often experience diarrhea that can persist long after the infection has ended. This is especially true when antibiotics are taken for long periods of time. The reason for this is that antibiotics kill off many naturally occurring bacteria in the digestive tract, which can upset the balance of gut flora and allow harmful bacteria to thrive. Apart from this, probiotics also appear to be helpful for most other types of diarrhea including infectious diarrhea, motion sickness or chemotherapy-induced diarrhea (141, 142, 143). Probiotics can also combat irritable bowel syndrome - a common intestinal disorder - and reduce symptoms such as bloating, constipation, diarrhea and others (35, 36, 37). Some studies also report benefits in inflammatory bowel diseases such as Crohn's disease and ulcerative colitis (38). In addition, probiotics may help fight Heliobacter pylori infections, which is one of the main triggers of stomach ulcers and stomach cancer (39, 40, 41, 42).
If you suffer from digestive problems that just won't go away, it might make sense to consider using a probiotic, although you should of course consult a doctor first.
People who are obese have a different composition of intestinal flora than lean people (43). Interestingly, research conducted with animals suggests that fecal transplants from lean animals can help obese animals lose weight (44, 45).
For these reasons, many scientists believe that gut bacteria are important in determining body weight (46, 47). Although more research is needed, some probiotic strands appear to support weight loss (48).
In a study of 210 people with central obesity characterized by excessive amounts of abdominal fat, daily intake of the probiotic Lactobacillus gasseri resulted in a loss of 8.5% abdominal fat within 12 weeks (49). After the subjects stopped taking the probiotic, they regained all the abdominal fat they had lost within 4 weeks.
Scientific research also suggests that Lactobacillus rhamnosus and Bifidobacterium lactis may help with weight loss and obesity prevention, although more research is needed (50). In contrast, some studies conducted in animals show that other probiotic strands can lead to weight gain rather than weight loss (51).
Many scientists believe that the gut flora plays an important role in the pathogenesis and metabolic dysfunction of type 2 diabetes (4). The gut flora of adult diabetics is quite different from the composition of the gut flora of healthy adults.
Probiotics may help to improve carbohydrate metabolism, fasting blood glucose levels, insulin sensitivity and antioxidant status in diabetic patients (4, 52). Certain probiotics such as L. lactis and bifidobacteria secrete an insulin analog and can slightly improve fasting insulin levels in type 2 diabetics (53).
A number of human studies have shown that certain probiotics can lower blood glucose levels (52) and improve insulin sensitivity in people with metabolic syndrome.
In people with elevated cholesterol levels, daily consumption of certain probiotics can significantly reduce both total cholesterol levels and levels of bad LDL cholesterol (7, 55, 56). However, this effect was not observed in people with normal or borderline cholesterol levels (54).
Other studies have also observed that probiotics can increase levels of "good" HDL cholesterol in both diabetics and healthy young people (57, 58).
The probiotic L. Helveticus produces ACE inhibitory peptides that can potentially prevent high blood pressure or control existing high blood pressure (59). In fact, such a reduction in blood pressure has been observed in subjects with hypertension without side effects (60, 61, 62). In addition, a reduction in arterial stiffness was observed (63).
Similar antihypertensive effects have also been observed with a number of other probiotics (64, 65, 66, 67, 68).
According to some researchers, probiotics and prebiotics may help prevent or reduce the severity of cardiovascular disease, which can be attributed to a reduction in total cholesterol levels, levels of bad LDL cholesterol and a reduction in inflammation, among other things (7).
In addition, certain probiotics could protect against arteriosclerosis by inhibiting the absorption of cholesterol in the intestine and suppress plaque formation in the arteries by inhibiting the production of pro-inflammatory cytokines (69, 70, 71). A scientific study concludes that regular intake of the probiotic L. acidophilus could reduce the risk of coronary heart disease by 6 to 10% (72).
Intestinal bacteria cooperate with the host's immune system via a wide range of signaling pathways (7). Studies conducted with germ-free animals show that gut flora is necessary for the development and regulation of immune function in the gut, where it prevents the development of unwanted inflammation (73).
According to some scientists, probiotics may modify the immune system by stimulating the production of anti-inflammatory cytokines, down-regulating pro-inflammatory cytokines and modulating the white blood cell response (6). Probiotics have been shown to activate both innate and acquired immunity in humans (74, 75, 76, 77). They can prevent infections such as influenza and the common cold, as well as reduce the duration and symptoms of upper respiratory tract infections and other infections (78, 79, 80, 81).
Although the effects of prebiotics have been best studied for influenza and the common cold, other studies show that they can also help reduce the risk of wound infections (82), alleviate infectious diseases of the digestive tract (85), improve the effects of vaccinations (83), prevent rotavirus infections (84), inhibit Salmonella transmission (87), reduce urinary tract infections (88) and reduce the risk of sepsis (86).
Studies have shown that probiotics such as B. coagulans can increase protein absorption in trained men, thereby indirectly improving muscle recovery and increasing training adaptations (89). Furthermore, it has been shown that this probiotic can reduce muscle damage and soreness and maintain physical performance after strenuous training sessions (89). In addition, after 8 weeks of supplementation with this probiotic in combination with 4 full-body training sessions per week, a significant increase in vertical jump height was measured compared to the control group who trained without probiotic supplementation (89). In other studies, it was shown that a probiotic with different probiotic strands could delay the time to exhaustion in male runners (90). A study conducted with mice also concluded that probiotics could increase relative muscle weight, grip strength and endurance during swimming (91).
Various human studies have concluded that probiotics can alleviate the symptoms of rheumatoid arthritis and reduce inflammation associated with this condition by lowering levels of pro-inflammatory cytokines (92, 93). In addition, adjunctive treatment with probiotics has been shown to relieve pain, reduce perceived disability and improve the ability to walk longer distances in patients suffering from rheumatoid arthritis (94). In animal studies, probiotics have also been shown to reduce joint cartilage degradation and swelling, as well as increase levels of anti-inflammatory cytokines (95, 96, 97, 98). In another study, probiotics were even able to inhibit the development of arthritis (99). In addition to alleviating arthritis, probiotics can also improve bone health, partly due to increased absorption of calcium (100). In animals, administration of probiotics such as lactobacilli resulted in higher bone mineral density and more stable bones (101), and some probiotics have also been shown to prevent bone resorption and stimulate bone formation (102, 103).
Certain probiotics can increase the bioavailability of minerals such as calcium, phosphorus, magnesium, iron and zinc, based in part on a breakdown of phytates found in certain plants that can inhibit mineral absorption (104, 105, 106). In addition, it has been shown that certain probiotics can increase vitamin B12, vitamin B2, vitamin D3 and folate levels in the body (107, 110), partly because these vitamins can be produced by some probiotic bacteria in the gut (108, 109, 111).
Studies have shown that various probiotics and combinations of probiotics can reduce the levels of inflammatory markers in various inflammatory conditions. These effects were observed in both locally isolated and body-wide inflammation (52, 112, 113, 114).
These effects appear to be based, at least in part, on the fact that probiotics inhibit the release of pro-inflammatory cytokines and stimulate the release of anti-inflammatory cytokines, while at the same time increasing the activity of natural killer cells of the immune system (115, 116, 117).
When heavy metals are ingested through food, even small amounts can have devastating effects on the body. Some probiotics have been shown to reduce this health burden by binding toxic heavy metals such as cadmium and lead and thus preventing their absorption (118). In addition, probiotics have also been shown to significantly reduce uptake and accumulation in body tissues of other potentially toxic compounds such as aluminum, pesticides, heterocyclic aromatic amines and others (119, 120, 121, 122).
Gut bacteria play a primary role in the bidirectional communication between the gut and brain, also known as the gut-brain axis (25). It is now generally accepted that gut bacteria can influence behavior and cognitive function (8).
Scientific studies have shown that probiotics can improve spatial and non-spatial memory (123) and reduce impairments in brain function in animals caused by drugs such as scopolamine or neurological diseases such as neuritis or dementia (124, 125, 126, 127, 128).
Studies have also shown that probiotic bacteria can improve mood, reduce anxiety and even alleviate depression (25, 129, 130, 131). This may be due to the fact that some gut bacteria are able to produce neuroactive substances such as serotonin and GABA and deliver them to the brain (25, 132).
In addition, some probiotics have neuroprotective properties that can reduce or prevent damage to the brain and nerve cells (135).
Probiotics are generally well tolerated and are considered safe and harmless for most people. However, it is not recommended to take probiotics without medical supervision if you are seriously ill or suffer from impaired immune system function. There are reports of rare cases of sepsis, endocarditis and liver abscesses while using lactobacilli.
During the first few days of use, there may be digestive-related side effects such as flatulence and mild digestive discomfort (29). However, once the body has adapted, digestion should improve.
In people with compromised immune function, including HIV and AIDS patients, probiotics can lead to dangerous infections (30).
You can take probiotics in the form of a range of different foods or supplements.
Live probiotic cultures are often found in fermented dairy products such as yogurt and certain milk drinks. Fermented foods such as pickled vegetables, tempeh, miso, kefir, kimchi, sauerkraut and fermented soy products may also contain some lactic acid bacteria.
Alternatively, you can take probiotics in the form of tablets, capsules or powder, which contain these bacteria in dried form. Probiotic products are available in capsule, tablet and powder form. To overcome the problem that some probiotics are unable to survive transit through the stomach, microencapsulated products have been developed.
However, although some probiotic strands do not survive transit through the stomach, even their dead form can be useful. These non-living probiotics are known as "para-probiotics" or "ghost probiotics" and have been shown in rat studies to enhance anti-inflammatory effects in rats with colitis, protect against certain harmful fungi and inhibit the growth of cancer cells (6).
Each probiotic species occurs in many different strands. Some of the properties of each species may be specific to the strand or may vary between strands.
Maintaining a healthy digestive tract is about more than simply taking a probiotic supplement. Daily diet and exercise are just as important, as many lifestyle factors affect gut bacteria.
However, probiotic supplements offer a wide range of benefits with minimal side effects. So they might be worth a try if you want to improve the health of your digestive tract.
