The chapter gives the underlying scientific principles and food-based guidelines for dietary recommendations in a wide range of clinical conditions such as diarrhoea, constipation, peptic ulcer, belching, flatulence, gluten-sensitive enteropathy, diabetes mellitus, coronary artery disease, congestive heart failure, hepatitis, chronic renal disease, urinary calculi, gout, phenylketonuria, galactosaemia, lactose intolerance, and post-operative states.