Probiotics are one of those pills that you see literally everywhere. You can get them on supermarket shelves, in pharmacies, even in your local health food store. There are endless products that have a label proudly extolling their probiotic content – pretty much anything even vaguely health-themed will probably have some reference to probiotics somewhere. There are millions of viral videos on every platform telling you to up your probiotic intake for everything from better gut health to better immune defense.Why is everyone recommending probiotics? It's an interesting question, because the evidence behind these pills is not nearly as robust as you might believe. When we say probiotics, we're generally referring to several species of bacteria that live in our guts and are associated with good health. For example, higher levels of bifidobacteria in your gut are associated with lower rates of obesity, and lower levels of lactobacillus are associated with a higher risk of heart attacks.The idea, therefore, is to give people pills or supplements containing these potentially beneficial bacteria. If we can alter the gut microbiome, we could make people healthier and reduce their risk of all sorts of nasty health problems.The issue with this idea is that your gut is very complicated, and adding a single bacterial strain to your diet is very simple.