Diet, lifestyle and environment do not just affect a person's health, they also determine the health of their children and possibly the health of their grandchildren. Mental ill health is an epidemic worldwide because of the combined effect of the modern diet and a sedentary lifestyle. Primary prevention of mental ill health starts, crucially, with optimal adult nutrition before the inception of pregnancy, includes breastfeeding, and continues throughout the life of the newborn. Obesity in pregnancy and poor human nutrition must be tackled head on. Nanocellulose and calorie-free monk fruit extract could be used to lower the energy density of processed foods/drinks (< 1.6 kcal g−1), and their bioavailable brain nutrient content including cofactors can be increased using bioactive encapsulation. Aquatic biotechnology can provide all the nutrients needed to make processed foods really nutritious. The nutritional value of processed and farmed foods should be based on the nutritional value of the late Palaeolithic human diet to help prevent mental ill health and other postprandial insults. After all, disease prevention, in the long run, is far less costly than treatment.