We introduce a state-space, geometrical approach that has previously been derived and tested using non-human animals and aim to demonstrate that it has the potential to generate testable hypotheses and provide novel insights into human nutrition and diet selection. This 'Geometric Framework' is unusual in that it focuses on the interactions between dietary constituents, and thus emphasizes the manner in which organisms regulate the balance of nutrients ingested. We report results from a pilot study, which indicate that protein ingestion is more strongly regulated than carbohydrate+fat. On the basis of these results and a brief survey of other experimental and population-level data, we hypothesize that regulation of protein intake may explain more of the modern human nutritional condition than has previously been appreciated.