Nutritional science has undergone a profound revolution in that time. For most of the 20th century it aimed to define an adequate diet. It determined our body’s minimal requirements for chemical building blocks (protein, minerals, fatty acids), for essential cogs in its machinery (vitamins), and for the energy it needs to run and maintain itself from day to day. Toward the end of the century, it became clear from laboratory studies and comparisons of health statistics in different countries that the major diseases of the adequately nourished developed world—cancer and heart disease—are influenced by what we eat. Nutritional science then began to focus on defining the elements of an optimal diet. So we discovered that minor, nonessential food components can have a cumulative effect on our long-term health. And plants, the planet’s biochemical virtuosos, turn out to be teeming with trace phytochemicals— from the Greek phyton, meaning “leaf”— that modulate our metabolism.