Public health nutrition is concerned with promoting good health and preventing non-communicable diseases. This chapter describes the average UK diet and takes the reader through the evidence that lies behind public health recommendations for healthy eating. This includes an examination of protein, carbohydrates, fats, vitamins and minerals, processed foods, red and processed meat, and fruit and vegetables. The chapter discusses several examples of diet-related diseases in adults such as osteomalacia, osteoporosis, megaloblastic and iron deficient anaemia, cardiovascular disease, type 2 diabetes and cancer. It includes evidence-based nutritional advice for pregnancy and mental health and wellbeing. The chapter presents food-based healthy-eating guidelines such as the Mediterranean diet, Eatwell Guide and planetary health diet. Finally, it acknowledges that food and eating happen within a context of marketing, health claims, fortification and culture.