The importance of diet in relationship to optimal health has been understood by healers throughout recorded history. Although it is well-known that Hippocrates regarded food as a primary form of medicine 2,500 years ago, his teachings on the subject were predated by the ancient Egyptians millennia earlier. Perhaps the oldest known evidence of man's understanding of proper diet are Egyptian pictographs from approximately 5,000 BC, which clearly point out the link between food and health. Egyptian papyrus records from 1,500 BC also show that the Egyptians employed specific foods to treat assorted disease conditions. Diet has also been an integral element of Ayurvedic and traditional Chinese medicine (see chapters 3 and 4) since their inception thousands of years ago.

Following Hippocrates, dietary recommendations continued to be made throughout subsequent centuries by such healers as Galen, Maimonides, and Paracelsus, but true scientific understanding of diet did not occur until the 18th century, beginning with the work of French physicist Rene de Reaumur, who is credited with conducting the initial research of digestive chemistry. Later in that same century, Reaumur's work was built upon by chemist Antoine Laurent Lavoisier, who, prior to being guillotined during the French Revolution, provided the scientific foundation for the study of how the body metabolizes food to create energy. The first person to show a direct link between disease and a lack of a specific nutrient, however, was James Lind, a physician in the British navy, who discovered that sailors on long voyages without rations containing citrus fruits developed bleeding gums, rough skin, poor muscle tension, and slow-healing wounds, all symptoms characteristic of scurvy. In 1757, in one of the first controlled medical experiments, Lind demonstrated that when sailors were supplied with lemons, limes, and oranges, scurvy could be prevented. As a result of his findings, Captain James Cook made it mandatory that every English sailor be supplied with rations of lemons and limes, enabling to sail around the world scurvy-free, as well as supplying them with the nickname "limeys." Today, it is well known that scurvy is due to vitamin C deficiency.

Throughout the 19th century, naturopathic physicians (see Chapter Eleven) also began their use of dietary therapy, along with fasting methods, to cleanse the body and stimulate its ability to heal. During the same century, further scientific discoveries established a link between other nutrients and various illnesses. In 1838, for instance, the Swedish chemist Baron Jons Jakob Berzelius discovered the link between iron and hemoglobin production, leading to the use of iron-rich foods to treat anemia. In 1897, Dutch physician Christiaan Eijkman proved that an element in unpolished rice was essential to proper functioning of the nervous system and carbohydrate metabolism, and that a deficiency in that ingredient could cause beriberi and other diseases. In 1929, his research resulted in him sharing the Nobel Prize with British biochemist Sir Frederick Gowland Hopkins for physiology and medicine.

The beginning of the 20th century heralded a new understanding of nutrition, beginning with Hopkins' work, which was pivotal in determining that in order for life to be sustained other nutritional factors beside proteins, carbohydrates, lipids (fats), and sodium were required. Hopkin's research pioneered the study of vitamins, and later resulted in his discovery of the amino acid L-tryptophane and the essential role it played in various life processes. It was Polish-American biochemist Casimir Funk, who actually named the nutritional factors Hopkins was researching, by coining the term vitamine, which was later changed to the more familiar vitamin. In 1911, building on Eijkman's research, he isolated the pure chemical from yeast and rice polishings that later became known as vitamin B-1, or thiamine, and his research regarding other food factors contributed to modern science's better understanding of vitamin deficiency.

In 1913, American biochemist Elmer McCollum discovered the first vitamin, which was designated vitamin A precisely for that reason. Another important 20th century nutritional researcher was the Hungarian-American biochemist Albert von Szent-Gyorgi, who was awarded the Nobel Prize for physiology or medicine in 1937 for his discovery of vitamin C and his research into its role as a catalyst in cellular oxidation.

By the mid-1900s, researchers had isolated and identified more than 40 nutrients essential to health, and in 1940 the Food and Nutrition Board of the National Research Council of the National Academy of Sciences established Recommended Daily Allowances (RDAs) for many of them. (RDAs are now referred to as Reference Daily Intakes, or RDIs. See sidebar below.) As a result of such research, scientists and physicians alike gained a new understanding of how diet affects biochemistry, and by the 1960s, growing numbers of physicians began to use dietary and nutritional measures to treat a variety of disease conditions. Around the same time, two-time Nobel laureate Linus Pauling, Ph.D., one of the most accomplished biochemists and molecular biologists who ever lived, became a staunch advocate of vitamin C intake in large doses, including as a preventive and therapeutic measure for the common cold. Pauling firmly believed that daily supplementation of vitamins in optimum amounts, in addition to following a healthy diet, was the most important step that anyone could take to live a long and healthy live, and by following his own advice, he lived productively for 93 years. Dr. Pauling also coined the term orthomolecular medicine (see sidebar below) to describe the use of vitamins, minerals, and amino acids, and other nutrients in optimum dosages to treat disease.

Another important researcher in the history of nutritional medicine is Denham Harman, M.D., who in 1956 pioneered the free-radical theory of aging. based on Denham's research, scientists now know that cell damage caused by free radicals (toxic singlet oxygen molecules) not only accelerates the aging process, but also contributes to numerous disease conditions, including cancer and cardiovascular disease. Harman and other researchers have also shown that the oxidizing effects of free radical activity can be minimized or reversed by antioxidant nutrients such as vitamins C and E, and today antioxidant multivitamin/mineral supplements are widely recommended by conventional and holistic physicians alike.