Diet quality, a term subject to change over time.

A high-quality diet is one of the foundations of health and well-being. For a long time in human history, diet was chiefly a source of energy and macronutrients meant to still hunger and give the strength for work and activities that were in general much harder than nowadays. Only few persons could afford to emphasize enjoyment. In the assessment of quality, organoleptic properties were major criteria to detect spoilage and oxidative deterioration of food. Today, food hygiene is a quality aspect that is often taken for granted by consumers, despite its lack being at the origin of most food-borne diseases. The discovery of micronutrients entailed fundamental changes of the concept of diet quality. However, non-essential food components with additional health functions were still barely known or not considered important until recently. With the high burden of obesity and its associated diseases on the rise, affluent, industrialized countries have developed an increased interest in these substances, which has led to the development of functional foods to optimize special body functions, reduce disease risk, or even contribute to therapeutic approaches. Indeed, nowadays, high contents of energy, fat, and sugar are factors associated with a lower quality of food, and products with reduced amounts of these components are valued by many consumers. At the same time, enjoyment and convenience are important quality factors, presenting food manufacturers with the dilemma of reconciling low fat content and applicability with good taste and appealing appearance. Functional foods offer an approach to address this challenge. Deeper insights into nutrient-gene interactions may enable personalized nutrition adapted to the special needs of individuals. However, so far, a varied healthy diet remains the best basis for health and well-being.