<P> In 1896 Eugen Baumann observed iodine in thyroid glands . In 1897, Christiaan Eijkman worked with natives of Java, who also suffered from beriberi . Eijkman observed that chickens fed the native diet of white rice developed the symptoms of beriberi, but remained healthy when fed unprocessed brown rice with the outer bran intact . Eijkman cured the natives by feeding them brown rice, demonstrating that food can cure disease . Over two decades later, nutritionists learned that the outer rice bran contains vitamin B </P> <P> In the early 20th century Carl von Voit and Max Rubner independently measured caloric energy expenditure in different species of animals, applying principles of physics in nutrition . In 1906, Wilcock and Hopkins showed that the amino acid tryptophan was necessary for the survival of rats . He fed them a special mixture of food containing all the nutrients he believed were essential for survival, but the rats died . A second group of rats to which he also fed an amount of milk containing vitamins . Gowland Hopkins recognized "accessory food factors" other than calories, protein and minerals, as organic materials essential to health but which the body cannot synthesize . In 1907 Stephen M. Babcock and Edwin B. Hart conducted the single - grain experiment . This experiment ran through 1911 . </P> <P> In 1912 Casimir Funk coined the term vitamin to label a vital factor in the diet: from the words "vital" and "amine," because these unknown substances preventing scurvy, beriberi, and pellagra, were thought then to derive from ammonia . The vitamins were studied in the first half of the 20th century . In 1913 Elmer McCollum discovered the first vitamins, fat - soluble vitamin A and water - soluble vitamin B (in 1915; later identified as a complex of several water - soluble vitamins) and named vitamin C as the then - unknown substance preventing scurvy . Lafayette Mendel (1872 - 1935) and Thomas Osborne (1859--1929) also performed pioneering work on vitamins A and B. In 1919 Sir Edward Mellanby incorrectly identified rickets as a vitamin A deficiency, because he could cure it in dogs with cod - liver oil . In 1922 McCollum destroyed the vitamin A in cod liver oil but found it still cured rickets, thus identifying vitamin D. Also in 1922, H.M. Evans and L.S. Bishop discovered vitamin E as essential for rat pregnancy, and originally called it "food factor X" until 1925 . </P> <P> In 1925 Hart discovered that iron absorption requires trace amounts of copper . In 1927 Adolf Otto Reinhold Windaus synthesized vitamin D, for which he won the Nobel Prize in Chemistry in 1928 . In 1928 Albert Szent - Györgyi isolated ascorbic acid, and in 1932 proved that it is vitamin C by preventing scurvy . In 1935 he synthesized it, and in 1937 won a Nobel Prize for his efforts . Szent - Györgyi concurrently elucidated much of the citric acid cycle . In the 1930s William Cumming Rose identified essential amino acids, necessary protein components which the body cannot synthesize . In 1935 Eric Underwood and Hedley Marston independently discovered the necessity of cobalt . In 1936 Eugene Floyd Dubois showed that work and school performance relate to caloric intake . In 1938 Erhard Fernholz discovered the chemical structure of vitamin E. It was synthesised by Paul Karrer (1889--1971). </P>

What is the normal diet for a human