For animals as well as people, diet affects what grows in the gut. The gut microbial colonies, also known as the gut microbiome, begin to form at birth. Their composition affects how the immune system develops and is linked to the later onset of metabolic diseases such as obesity. Common wisdom is that cats, by nature carnivorous, are healthiest when fed high-protein diets. Researchers wanted to find out if this is true.

Source: Kittens: Their microbiomes are what they eat