Measuring natural abundance of C-13 in respired CO2: variability and implications for non-invasive dietary analysis

S E Perkins, J R Speakman

Research output: Contribution to journalArticle


1. Three experiments were performed, using laboratory mice (Mus musculus) as a model species, to evaluate the potential of using measurements of carbon isotope ratios in expired CO2 for tracing diets.

2. Breath C-13 signatures of mice fed a constant diet (-21.4 parts per thousand +/- 0.35) reflected their diet, but were depleted by on average -5.7 parts per thousand. Body mass, sex and age were independent and significant factors correlated with the variability of C-13 enrichment in respired CO2.

3. Breath C-13 signatures from starved mice (7 h) were lower than unstarved mice by 2.0 parts per thousand. Subsequently when starved mice were fed a small meal of a new diet, breath C-13 signatures approached those of the new diets within 15 min, returning to preingestion levels after 105 min.

4. After a permanent diet switch C-13 values of breath were not asymptotic within 6 days, possibly because of use of fat reserves during the daytime carrying an isotopic memory of the previous diet. Hence, individual breath C-13 signatures may vary according to nutritive state and previous dietary history.

5. Interindividual variability was measured at 3.3 parts per thousand. The implications are that large samples of individuals will be required to distinguish between diets of different populations where the isotopic difference between their diets was small - for example, that expected between herbivorous and carnivorous diets. However, breath would be suitable for distinguishing between dietary intakes of individuals for food types that are isotopically more distinct - such as between C-3 and C-4 plants.

Original languageEnglish
Pages (from-to)791-797
Number of pages7
JournalFunctional Ecology
Publication statusPublished - 2001


  • breath samples
  • carbon 13
  • diet tracing
  • isotopic signatures
  • Mus musculus
  • DELTA-C-13


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