Suez and colleagues investigated the recovery of the gut microbiota after antibiotic treatment and found that probiotics might perturb rather than aid this process. The probiotics rapidly colonised the gut but prevented the normal microbiota from repopulating for up to 5 months. While likely to be considerably less appealing, the group who received autologous faecal microbiota transplantation recovered their microbiota the quickest, with the composition of the microbiota returning to normal within days. Furthermore, Zmora and colleagues showed that colonisation occurred in highly individualised patterns, with some people's gastrointestinal tracts rejecting probiotics and others allowing colonisation by the probiotic strain, meaning that many individuals taking probiotic supplements are simply wasting their money.
Most probiotics are like what is already in a person's digestive system. Some probiotics have been used for a very long time throughout history, such as in fermented foods and cultured milk products. These don't appear to cause illness. But more study is needed on the safety of probiotics in young children, the elderly, and people who have weak immune systems.
Importantly, patients with gastrointestinal conditions are not the only ones taking probiotics. 3·9 million people in the USA alone regularly take probiotic supplements, with promised benefits ranging from improved digestion and immune function to improved mental health and prevention of heart disease. However, evidence for these benefits is lacking, and because probiotics are often sold as supplements, manufacturers in many countries are not required to provide evidence of their safety and efficacy to regulatory bodies. The ubiquity of probiotic products would suggest that, at worst, they are harmless. Nevertheless, some safety concerns have been raised, including the risk of contamination, possibility of fungaemia or bacteraemia (particularly in immune-compromised, elderly, or critically ill individuals), small intestinal bacterial overgrowth, and antibiotic resistance. Adding to concerns, clinical trials of probiotics have not consistently reported safety outcomes.

Most probiotics are like what is already in a person's digestive system. Some probiotics have been used for a very long time throughout history, such as in fermented foods and cultured milk products. These don't appear to cause illness. But more study is needed on the safety of probiotics in young children, the elderly, and people who have weak immune systems.
Our gut is home to over 500 bacterial species. These “visitors” form a bioreactor, which facilitates digestion, provides nutrients, and helps form the immune system. Some important nutrients made by this bioreactor include several B vitamins, vitamin K, folate, and some short-chain fatty acids. Up to 10% of an individual’s daily energy needs can be derived from the byproducts of the good bacteria in your gut.
A closer look at the science underlying microbe-based treatments, however, shows that most of the health claims for probiotics are pure hype. The majority of studies to date have failed to reveal any benefits in individuals who are already healthy. The bacteria seem to help only those people suffering from a few specific intestinal disorders. “There is no evidence to suggest that people with normal gastrointestinal tracts can benefit from taking probiotics,” says Matthew Ciorba, a gastroenterologist at Washington University in St. Louis. “If you're not in any distress, I would not recommend them.” Emma Allen-Vercoe, a microbiologist at the University of Guelph in Ontario, agrees. For the most part, she says, “the claims that are made are enormously inflated.”
An imbalance in the gut microbiota is believed to contribute to a number of health problems, particularly gastrointestinal issues, as well as immune dysfunction and infections. The bacterial balance can be disrupted by medical conditions, emotional and physical stress, and, most notably, use of antibiotics, which destroy the good bacteria along with the bad. 

The takeaway: Certain strains were found useful in preventing diarrhea among children being prescribed antibiotics. A 2013 review showed that after antibiotic use, probiotics help prevent Clostridium difficile-associated diarrhea. A review focused on acute infectious diarrhea found a benefit, again for certain strains of bacteria at controlled doses. There’s also evidence that they may help prevent necrotizing enterocolitis (a serious gastrointestinal condition) and death in preterm infants.
An imbalance in the gut microbiota is believed to contribute to a number of health problems, particularly gastrointestinal issues, as well as immune dysfunction and infections. The bacterial balance can be disrupted by medical conditions, emotional and physical stress, and, most notably, use of antibiotics, which destroy the good bacteria along with the bad.
Though capsules are ideal for quick, convenient consumption, powdered products are a great choice for anyone who wants to mix their probiotics with shakes or smoothies. The Hyperbiotics Organic Prebiotic Powder is a totally taste-free prebiotic powder that has inulin, FOS, resistant starch, and dietary fiber to help keep your gut health in line. Unlike probiotics, prebiotics works to nourish and grow the bacteria that is already in your body. This supplement also has acacia fiber, which is said to help suppress appetite and reduce gas and bloating. You can take between one and three scoops of powder a day, depending on how much microbial support you’re looking for. Each container comes with 375 grams or roughly 54 servings, and it doesn’t need to be refrigerated.
They probably are. Lebwohl says probiotics may decrease the risk of getting diarrhea during the course of taking antibiotics, and may also play a role in specifically preventing the development of the dreaded antibiotic-related super diarrhea called C. difficile or C. diff. Antibiotics can wipe out the good bacteria that keep you from getting sick if you’re exposed to C. diff, or if you already have it in your system. C. diff symptoms can range from a moderate watery diarrhea several times a day to severe infections, which can be accompanied by fever, bloody stools, rapid heart rate, and can even lead to kidney failure. 500,000 Americans were infected with C. diff in 2015 and 15,000 died from it.
Nevertheless, the presence of certain bacteria in the lower gut benefits overall health, not only digestion. The science on the role of the lower gut is changing every day and has advanced significantly — even over the past 10 years. Research strongly suggests that a favorable bacterial balance in the lower gut positively affects the factors influencing heart disease, immunity, bone strength, depression, and obesity and weight loss. Science has only just begun to determine the roles that bacteria play in human health, but it seems clear that healthier people have healthier bacterial balances. People with poorly balanced bacteria levels are more likely to suffer serious health problems.
If you have an immune system problem or another serious health condition, you may have a greater chance of issues. Some reports have linked probiotics to serious infections and other side effects. The people most likely to have trouble are those with immune system problems, people who've had surgery, and others who are critically ill. Don't take probiotics if you have any of those issues.
What exactly do probiotics do? They are believed to protect us in two ways. The first is the role that they play in our digestive tract. We know that our digestive tract needs a healthy balance between the good and bad bacteria, so what gets in the way of this? It looks like our lifestyle is both the problem and the solution. Poor food choices, emotional stress, lack of sleep, antibiotic overuse, other drugs, and environmental influences can all shift the balance in favor of the bad bacteria.
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