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. 2025 Jan 30;57(1):13.
doi: 10.1007/s00726-024-03425-2.

Amino acid stable carbon isotopes in nail keratin illuminate breastfeeding and weaning practices of mother - infant dyads

Hana Salahuddin  1 , Andrea L Waters-Rist  2 , Fred J Longstaffe  3
Affiliations

Amino acid stable carbon isotopes in nail keratin illuminate breastfeeding and weaning practices of mother - infant dyads

Hana Salahuddin et al. Amino Acids. .

Abstract

Compound-specific stable carbon isotope analysis of amino acids (CSIA-AA) is widely used in ecological studies to analyze food-webs and is gaining use in archaeology for investigating past diets. However, its use in reconstructing breastfeeding and weaning practices is not fully understood. This study evaluates the efficacy of stable carbon isotope analysis of amino acids in early life diet reconstruction by analyzing keratin from fingernail samples of three mother-infant pairs during late gestation and early postpartum periods. Our results show that stable carbon isotope ratios (δ13C) of glycine, and to a lesser extent glutamate, effectively trace the onset of exclusive breastfeeding and the end of weaning in infants. We propose that glycine's 'conditionally essential' metabolic pathway during infancy allows it to reflect maternal glycine δ13C, indicating breastmilk consumption. Subtle changes in glutamate δ13C likely result from its 'non-essential' status. Additionally, δ13C values of glycine and glutamate indicate maternal physiological and pathological stress due to catabolic effects such as gluconeogenesis. These findings have significant implications for ecological and archaeological research using CSIA-AA for dietary reconstructions. They highlight the need to understand how metabolic pathways affecting δ13C of amino acids may change over an individual's lifespan or be altered due to various forms of stress.

Keywords: Amino acids; Breastfeeding; Isotope analysis; Weaning.

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Conflict of interest statement

Declarations. Competing interest: The authors declare that there are no known financial interests or personal relationships that could have influenced the work reported in this article. All study participants gave their informed consent for inclusion before partaking in the study. This study is in accordance with the Tri-Council Policy Statement Ethical Conduct for Research Involving Humans (TCPS2) and the Ontario Personal Health Information Protection Act (PHIPA, 2004). The protocol used in this study was approved by the Non-Medical Research Ethics Board of Western University (Project ID 119889).

Figures

Fig. 1
Fig. 1
Stable carbon isotope profile for (a) Gly and Glx of CHIL 1 and Gly of MOM 1, (b) Gly and Glx of CHIL 2 and Gly of MOM 2 and (c) Gly and Glx of CHIL 3 and Gly of MOM 3. Zero represents birth. Error margins are 4 weeks for mothers, 2 weeks for infants, with δ¹³CGly and δ¹³CGlx analytical errors of ± 1‰ and ± 2‰, respectively
Fig. 2
Fig. 2
Gly and Glx δ13C for (a) MOM 1 from 22 weeks prior to and 19 weeks after delivery (red boxes mark the periods of stress), and (b) MOM 3 from 25 weeks prior to and 6 weeks after delivery. Zero represents the week of delivery. The error margin for the time period represented by each sample is 4 weeks with δ¹³CGly and δ¹³CGlx analytical errors of ± 1‰ and ± 2‰, respectively
See this image and copyright information in PMC

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