ABSTRACT
Experiments stretching back over the last two centuries have demonstrated the principle that all animals require an exogenous supply of protein. In humans, and in other non-ruminating mammals, this protein must be present in the food they eat. (Some ruminants can survive without dietary protein if their diet contains alternative sources of nitrogen. This is because bacteria in the rumen can make protein from non-protein nitrogen sources such as urea, and the animals can digest and absorb this bacterial protein.)
In the early 1800s, François Magendie fed dogs with single foods that were regarded as highly nutritious but lacked any nitrogen (e.g. sugar, olive oil or butter). These unfortunate dogs survived much longer than if they had been completely starved, but they lost weight, their muscles wasted dramatically and they all died within 40 days. Several modern writers, including myself, had assumed that Magendie completed the cycle of evidence by showing that the dogs recovered when nitrogen-containing foods were added back to their diets. In his excellent book on the history of protein nutrition, Carpenter (1994) points out that Magendie did not actually do these positive controls. Despite this he is still usually credited with the discovery that nitrogen-containing foods are essential in the diet. In later years it became clear that Magendie’s initial conclusions were correct: adequate amounts of nitrogen-containing
foods were essential to allow growth and even survival in experimental animals. Such experiments demonstrated the need for nitrogencontaining foods (i.e. protein) even before the chemical nature of dietary protein was known.
