Stable Isotope Dietary Reconstruction
Stable isotope dietary reconstruction uses carbon and nitrogen ratios in bone collagen and apatite to estimate the foods that made up past diets, including the role of C4 plants such as maize, marine resources, and animal protein.
Definition
The reconstruction of past diet from the ratios of stable carbon and nitrogen isotopes preserved in bone and tooth collagen and mineral, interpreted against known dietary and ecological baselines.
Scope
This topic covers the measurement and interpretation of carbon and nitrogen stable isotopes in skeletal tissues to reconstruct diet: distinguishing C3 from C4 plant consumption, marine from terrestrial protein, and trophic level, as well as reconstructing weaning from nitrogen profiles. It addresses tissue-diet fractionation, baseline and ecosystem variation, and quality-control screening for diagenetic alteration of collagen.
Core questions
- How do carbon and nitrogen isotopes distinguish plant types, marine foods, and trophic level?
- How is the introduction of crops such as maize detected isotopically?
- How can weaning age be reconstructed from nitrogen isotope profiles?
- How is diagenetic alteration of collagen screened to ensure reliable signals?
Key theories
- Trophic-level enrichment
- The principle that nitrogen isotope ratios increase by a roughly constant step with each step up the food chain, allowing reconstruction of the importance of animal versus plant protein and the detection of breastfeeding as a trophic level above the mother.
- Collagen quality control
- DeNiro's demonstration that diagenetic alteration changes collagen carbon-to-nitrogen ratios, providing a screening criterion to reject contaminated samples before dietary interpretation.
History
Dietary isotope analysis began around 1980 when carbon isotopes revealed the spread of maize in eastern North America, and nitrogen isotopes were soon added to assess trophic level and marine diets. DeNiro's work on collagen quality established essential screening standards, and the method became a routine tool for studying subsistence transitions and infant feeding.
Debates
- Baselines and the resolution of dietary signals
- How precisely diet can be reconstructed given variation in environmental baselines, uncertainties in fractionation factors, and the mixing of multiple food sources, and whether bulk-collagen values can be over-interpreted.
Key figures
- Stanley H. Ambrose
- Michael J. DeNiro
- Julia A. Lee-Thorp
Related topics
Seminal works
- ambrose1993
- deniro1985
- leethorp2008
Frequently asked questions
- How do isotopes reveal maize in the diet?
- Maize is a C4 plant with a distinctive carbon isotope signature, so its adoption shifts the carbon isotope values of bone collagen in a way researchers can detect and date.
- Can isotopes show when infants were weaned?
- Yes—nursing infants have elevated nitrogen isotope values reflecting consumption of their mother's tissues, and the decline of these values as solid foods are introduced tracks the weaning process.