At all stages of life, humans are associated with microorganisms and their products. Diet plays a crucial role in shaping the composition of the gut microbiome. Different dietary patterns, such as vegan, vegetarian, and omnivorous diets, result in distinct microbiome profiles. Recent research is rapidly strengthening the appreciation that associated microorganisms make essential contributions to human health and well-being. A low diversity of microorganisms is associated with a plethora of diseases including allergy, diabetes, obesity, arthritis, inflammatory bowel diseases and even neuropsychiatric disorders. Thus, an interaction of microorganisms with the host immune system is required for a healthy body. The microbiome in humans is also not constant during lifespan, but rather changes with age. Culture and location also have a profound impact on the microbiome. Diet is a particularly important factor in determining the microbiota composition of the gut. Thus, vegans, vegetarians and omnivores have distinct microbiomes.