Over the course of decades, scientists have conducted fascinating investigations into human nutrition, discovering, demon-strating, and confi rming the fundamental role that food and nutrients fulfi ll in human life. As elucidated in this volume, among the many important functions of nutrients are enabling growth and development, preventing disease, and providing energy for activities ranging from chemical reactions in cells to the contraction of muscles during exercise. The science of nutrition, as it is explored in these pages, offers readers insight into the inter- actions between nutrients and tissues, the properties of the nutrients themselves, and the role of nutrition in health and disease.

The journey begins with an exploration of the relationship between food and the human body. Food is a source of energy that the body accesses through the processes of digestion and metabolism. These processes free from foods the nutrients needed to fuel chemi- cal reactions and break down or build up materials such as tissues. The work of performing these activities is associated with the production of heat. This heat energy is measured in kilocalories or, put simply, cal- ories. The number of calories in food is determined using an instrument known as a bomb calorimeter, which mea-sures the amount of heat released when a food is burned completely.