According to a National Institutes of Health survey, the number of adults in the U. The popular frenzy surrounding probiotics is fueled in large part by surging scientific and public interest in the human microbiome: the overlapping ecosystems of bacteria and other microorganisms found throughout the body. The human gastrointestinal system contains about 39 trillion bacteria, according to the latest estimate, most of which reside in the large intestine.
In the past 15 years researchers have established that many of these commensal microbes are essential for health. Collectively, they crowd out harmful microbial invaders, break down fibrous foods into more digestible components and produce vitamins such as K and B The idea that consuming probiotics can boost the ability of already well-functioning native bacteria to promote general health is dubious for a couple of reasons.
Manufacturers of probiotics often select specific bacterial strains for their products because they know how to grow them in large numbers, not because they are adapted to the human gut or known to improve health. The particular strains of Bifidobacterium or Lactobacillus that are typically found in many yogurts and pills may not be the same kind that can survive the highly acidic environment of the human stomach and from there colonize the gut.
Even if some of the bacteria in a probiotic managed to survive and propagate in the intestine, there would likely be far too few of them to dramatically alter the overall composition of one's internal ecosystem.
Whereas the human gut contains tens of trillions of bacteria, there are only between million and a few hundred billion bacteria in a typical serving of yogurt or a microbe-filled pill. Last year a team of scientists at the University of Copenhagen published a review of seven randomized, placebo-controlled trials the most scientifically rigorous types of studies researchers know how to conduct investigating whether probiotic supplements—including biscuits, milk-based drinks and capsules—change the diversity of bacteria in fecal samples.
Only one study—of 34 healthy volunteers—found a statistically significant change, and there was no indication that it provided a clinical benefit. Despite a growing sense that probiotics do not offer anything of substance to individuals who are already healthy, researchers have documented some benefits for people with certain conditions.
In the past five years, for example, several combined analyses of dozens of studies have concluded that probiotics may help prevent some common side effects of treatment with antibiotics.
Whenever physicians prescribe these medications, they know they stand a good chance of annihilating entire communities of beneficial bacteria in the intestine, along with whatever problem-causing microbes they are trying to dispel. Normally the body just needs to grab a few bacteria from the environment to reestablish a healthy microbiome. But sometimes the emptied niches get filled up with harmful bacteria that secrete toxins, causing inflammation in the intestine and triggering diarrhea.
Adding yogurt or other probiotics—especially the kinds that contain Lactobacillus —during and after a course of antibiotics seems to decrease the chances of subsequently developing these opportunistic infections.
A review by Cochrane—an independent network of experts who serve as rigorous arbiters of medical research—found that probiotics may be particularly useful in a hospital's neonatal intensive care unit. The addition of beneficial bacteria to a nutritional regimen seems to significantly reduce the likelihood of developing necrotizing enterocolitis, which is a devastating, poorly understood and often fatal gut disease that primarily afflicts preterm infants—especially the smallest and most premature among them.
Researchers think that many cases of the disease begin with an opportunistic bacterial infection in the not yet fully developed intestine of an infant. But there's little evidence to support many health claims made about them. For example, there's no evidence to suggest that probiotics can help treat eczema. But for most people, probiotics appear to be safe. If you want to try them, and you have a healthy immune system, they shouldn't cause any unpleasant side effects.
Probiotics are generally classed as food rather than medicine, which means they don't go through the rigorous testing medicines do.
Once through the stomach, the probiotic bacteria embark on the next stage of their journey. Other strains may pass through the small intestine and take up residence when they reach the large intestine or bowel. Where probiotics choose to reside is governed predominantly by the specific conditions in different areas of the gut including pH levels of acidity or alkalinity , oxygen levels, and the type of bacteria in the microbiome 4.
Some areas of the gut have more oxygen available like the small intestine, whereas other areas have little or no oxygen like parts of the large intestine, making those areas only suitable for certain strains of bacteria that do not need oxygen to survive. Additionally, the pH differs at different points along the digestive tract, with the small intestine typically being more acidic than the large intestine.
Although, as we have learned, it can be a challenge for probiotic bacteria to travel through the highly acidic stomach, which can reach acidity levels of around pH 1. It is important to choose a probiotic supplement which contains strains that have been proven to reach the gut alive. It is commonly believed that probiotics need to be taken in enteric-coated capsules to protect the probiotics as they pass through the stomach before being released into the gut.
This is not necessary for probiotic strains which are resilient and able to reach the gut without damage. Learn more about common probiotic myths by reading The Survival M. The good bacteria compete with pathogens for both their food sources and space in which to live, making it difficult for the undesirable bacteria to survive 9. Probiotics also produce certain acids 10 which discourage pathogen growth, whilst improving the gut environment for their own benefit and for the benefit of other types of good bacteria, which also begin to grow in numbers.
When the gut microbiome comes into balance with increased levels of beneficial bacteria and reduced levels of pathogenic bacteria, the individual may notice an improvement in their digestion and wellbeing. This is because gut pathogens produce many toxins 11 and other substances that negatively affect our health, whereas probiotic strains of bacteria produce beneficial substances, including certain vitamins and short-chain-fatty-acids that have a positive impact on our overall health.
Our gut is home to a delicate ecosystem of microbes, and many factors affect which strains flourish, and which ones may struggle.
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