There was a time when every Indian household had its own unwritten rules about food. Curd set at home, a bowl of khichdi during illness, fermented batter waiting overnight in the kitchen and a spoonful of ghee over steaming rice were not wellness trends. They were simply everyday habits.Now, science appears to be catching up with what grandmothers have known for generations.The gut is increasingly being described as the body's "second brain". Researchers are finding that the trillions of microbes living inside the digestive system influence far more than digestion. Immunity, metabolism, inflammation, mood, sleep quality and even skin health are all linked to the gut microbiome.