Frank I. Katch


Santorio experiments breakthrough
in energy metabolism


Justus von Liebig (1803-1873)
After studying in France with eminent scientist Gay-Lussac, Liebig became Professor of Chemistry at the University of Giessen when he was only 21. He dominated both organic chemistry and, after 1840, agricultural chemistry. In later years his ideas about the proper constituents of fertilizers were criticized because the benefits could not be substantiated. Like other innovators, he fought with influential chemists such as Jean Baptiste Dumas, whom he accused of plagiarism (Carpenter, 1994; Gardner, 1972).

Although embroiled in professional controversies, Liebig established a large, modern chemistry laboratory that attracted numerous students. He developed unique equipment to analyze inorganic and organic substances.

Early drawing of Liebig's chemistry lab at the University of Giessen.

Liebig restudied protein compounds (alkaloids previously discovered by the chemist Mulder), and concluded that muscular exertion by horses or humans required mainly protein, not carbohydrate and fat. Liebig's influential Animal Chemistry (1842) communicated his ideas about energy metabolism (Carpenter, 1994):

The turnover of proteinaceous foods by adult animals, as shown by the continued excretion of urea even when none of these materials is consumed, is explained by muscles consuming themselves when they exert their muscular force. This force is released by the molecule breaking into fragments.

The breakdown of muscle that occurs during the day is compensated for by re-formation of tissues during sleep, and the "force" or vitality of the muscles is regained. For an active adult, 7 hours of sleep are required. An old man, who is necessarily less active, requires only 3.5 hours. In each case "waste is in equilibrium with supply." However, in the infant who sleeps 20 hours and is awake for only 4, there is an excess supply, and this explains the child's ability to gain weight and grow.

Since only those substances that are capable of conversion to blood can properly be called nutritious, or considered to be food, the protein elements of food are the only true nutrients, that is, the only ones capable of forming or replacing active tissue.

Someone who feels cold is induced to engage in physical activity. This stimulates respiration, part of which is needed for the breakdown of muscle fibers, but it admits more oxygen, which also results in more combustion of the non-nitrogenous protectors and, thus, in more heat production.

Because he so dominated chemistry, Liebig's theoretical pronouncements about the relation of dietary protein to muscular activity were generally accepted without review by other scientists until the 1850s. Guggenheim (1981) emphasizes the surprising fact that Liebig never carried out a physiological experiment or performed nitrogen balance studies on animals or humans. Liebig looked down on physiologists, believing them incapable of commenting on his theoretic calculations unless they themselves achieved his level of expertise.

Liebig's students became expert in glassblowing.

By mid century, physiologist Adolf Fick (1829-1901) and chemist Johannes Wislicenus (1835-1903) challenged Liebig's dogmatic pronouncements about the role of protein in exercise. Their simple experiment measured changes in urinary nitrogen during a mountain climb. The protein that broke down could not have supplied all the energy for their hike. The result discredited Liebig's principle assertion about the role of protein metabolism in exercise.

Although erroneous, Liebig's notions about protein as a primary exercise fuel worked their way into popular writings. By the turn of the 20th century, his idea that athletic prowess requires a large protein intake seemed unassailable. He lent his name to two commercial products: Liebig's Infant Food, advertised as a replacement for breast milk, and Liebig's Fleisch Extract (meat extract), which supposedly conferred special benefits to the body.

Two examples of product labels bearing Liebig's name that were marketed throughout Europe, forerunners of today's highly advertised (and successful) protein supplements.


Liebig argued that consuming his extract and meat would help the body perform extra "work" to convert plant material into useful substances (Holmes, 1974; Shenstone, 1895). Even today, fitness magazines tout protein supplements for peak performance with little except anecdotal confirmation (Carpenter, 1994). Whatever the merit of Liebig's claims, debate continues, building on the metabolic studies of previous history makers W. O. Atwater (1844-1907), F. G. Benedict (1870-1957), and R. H. Chittenden (1856-1943) in the United States, and M. Rubner (1854-1932) in Germany. Liebig, a giant in his field at the time, fell prey to a common dilemma: how to capitalize on commercial efforts while maintaining academic respectability. Unfortunately for Liebig, his dogmatic pronouncements and beliefs, rather than embracing truths discovered by experimentation and verification, clouded his many important discoveries in the embryonic field of nutritional biochemistry.


Carpenter, K. J. (1994). Protein and Energy: A Study of Changing Ideas in Nutrition. London: Cambridge University Press.

Gardner, E. J. (1972). History of Biology, Third edition. Minneapolis: Burgess Publishing Company.

Guggenheim, K. Y. (1981). Nutrition and Nutritional Diseases. Lexington, MA: Collamore Press.

Holmes, F. L. (1973). Justus von Liebig. Dictionary of Scientific Biography. Volume VII. New York: Charles Scribner's Sons.

Shenstone, W. A. (1895). Justus von Liebig: His Life and Work (1803-1873). New York: Macmillan.

Additional Resources 

Rossiter, M. W. (1974). The emergence of agricultural science: Justus Liebig and the Americans, 1840-1880. Ann Arbor, MI: University Microfilms.

Liebig's Chemical Letters, published by Peter Child, a lecturer in Chemistry at the University of Liimerick.

Photo of Liebig's chemistry laboratory from Justus-Liebig-Museum in Giessen.

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