Liebig’s foundational nutritional theory, stated in his 1847 Researches on the Chemistry of Food and elaborated in subsequent publications, held that albumin and related nitrogenous compounds were the essential nutritive principles of the diet. Muscular work, on this theory, was powered primarily by the catabolism of tissue protein, which was continuously rebuilt from dietary albuminoids. Meat extract, because it concentrated the water-soluble nitrogenous constituents of beef, was therefore represented as capturing the vital nutritive essence of meat in a portable and convenient form.

The claim was refuted on two fronts. Chemical analysis by August Almén (published in the Proceedings of the Upsala Medical Society) found that the extract contained very little usable protein; its nitrogen was largely in the form of creatine and creatinine, small molecules he characterised as waste products normally excreted via the kidneys and without nutritive value. Separately, Fick and Wislicenus’s 1865 Faulhorn self-experiment, and the Munich respiratory chamber studies of Voit and Pettenkofer from 1866 onward, showed that muscular work was fuelled by carbohydrates and fats at least as much as by protein, demolishing the theoretical premise that made meat extract a uniquely powerful restorative.