We carry up to 2 kilograms of microbes in our gut, and there are at least 1,000 species of bacteria consisting of over 3 million genes. Two thirds of the gut microbiome, or the population of microbes in the intestine, is unique to each individual.  This means that the food that we put into our bodies gets processed a bit differently by each of us.  It also means that our reaction to these foods that we eat to sustain us can vary.