Nitrogen Isotopes
The ratio of 15N/14N presents a characteristic distinction between herbivores and carnivores, as the movement up along the food chain tends to concentrate the 15N isotope, by 3-4‰ with each step of the food chain (terrestrial plants, with the exception of legumes, have an isotopic ratio of 2-6‰ of N). The tissues and hair of vegans therefore contain significantly lower percentage of 15N than the bodies of people who eat mostly meat. Isotopic analysis of hair is an important source of information for archaeologists, providing clues about the ancient diets; a terrestrial diet produces a different signature than a marine-based diet and this phenomenon has been used in analysing differing cultural attitudes to food sources.
Read more about this topic: Isotopic Signature