Early ideas on the nutritional significance of lipids

By 1824, Chevreul had demonstrated that fats were esters of glycerol and fatty acids of differing chain length. At the time, it was thought that fats could be synthesized only by the plant kingdom. However, by 1850, it had been found from balance studies that animals also could synthesize fats from carbohydrates. The caloric value of fat was determined in the 1860s and shown to be more than double that of carbohydrate. In 1907, it was shown that this was also true when fat was used as a source of energy for physical work. The special value of cod liver oil for the prevention and treatment of rickets was well known by 1850 but was not to be explained until much later.