Probiotics: what are they and how do they work?

Two studies published in Cell earlier this week raise concerns about the usefulness of probiotics and cast doubt on their safety, leading to the apprehension of consumers, providers and health care providers. But what exactly are probiotics? Who takes them? And how do the results of both studies fit into our existing knowledge base? Let's take a deeper look.

What are probiotics?

The term probiotic, which means "for life", refers to a multitude of living microorganisms that are thought to have beneficial effects on health. You can find them in your local grocery store as food (especially in dairy products such as yogurt), dietary supplements and even skin creams. Some people take probiotics daily to "maintain their balance" in their digestive system, while others use them as needed for various conditions – from irritable bowel syndrome to atopic dermatitis.

At a lower level, probiotics can be considered microscopic "microbes" designed to mimic the roles of natural bacteria in our bodies. Although we often consider bacteria and yeasts as harmful, many of these microorganisms play a crucial role in the functioning of our body. One of its most important functions is to cover the parts of the gastrointestinal tract, help foods digest, produce vitamins and fight the "bad" bacteria associated with the disease. For example, some species of lactobacilli, which are found in breast milk, are of paramount importance for the digestion of milk in infants. Likewise, certain types of E. Coli present in our intestines help us produce Vitamin K, an essential vitamin that promotes blood clotting.

Who takes probiotics?

According to the 2012 National Health Interview Survey, about four million adults (1.6%) and 300,000 children (0.5%) in the United States reported using probiotics during last 30 days. They are the third most used dietary supplement and their use quadrupled between 2007 and 2012.

Anne Cusack / Los Angeles Times via Getty Images

Do they work?

The first thing to keep in mind is that not all probiotics are the same and all are not the same, which makes it extremely difficult to study the effects of probiotics. Several epidemiological studies have shown positive results, particularly in the areas of improvement of intestinal health and immune response, while others have demonstrated a lack of efficacy or inconsistent results .

Researchers at the Weizmann Institute of Science in Israel, who were behind two Cell studies earlier this week, found that, contrary to popular belief, the probiotics we eat do not stay in the intestines . To work. Instead, they are excreted in our stools.

Previous probiotic studies have been found to have focused primarily on the bacterial profiles of stool specimens, rather than focusing directly on the intestinal contents. This has raised concerns about findings from previous studies. However, it is important to remember that the new Cell study was small and was not designed to evaluate whether probiotics work. Overall, the consensus is that we need additional studies to better understand the effects of probiotics.

Are they safe?

Historically, for healthy adults, it was thought that probiotics were relatively safe. When side effects occur, they tend to have mild digestive symptoms such as gas. However, in people who are seriously ill or have underlying medical problems, such as a weakened immune system, probiotics have resulted in serious side effects, including dangerous infections.

One of this week's cell studies found that probiotics administered after antibiotics delayed the return of the bacterial community from our intestines, known as the microbiome, to its normal, healthy pre-antibiotic state. This has raised concerns that probiotics may not be as harmless as we thought, even in healthy adults. But we do not yet know how these results translate clinically.

Although the details regarding the safety and efficacy of probiotics remain controversial, scientists and health professionals do not dispute that the safest and most effective way to promote intestinal and immune health is to simply to eat well. Balanced diet, rich in vegetables.

Dr. Nicky Mehtani is a physician in internal medicine at Johns Hopkins Hospital and is part of the ABC News Medical Unit.