Normal gastrointestinal temperature values measured through ingestible capsules technology: a systematic review

Climate change has amplified the importance of continuous and precise body core temperature (T_core) monitoring in the everyday life. In this context, assessing T_core through ingestible capsules technology, i.e., gastrointestinal temperature (T_{gastrointestinal}), emerges as a good alternative to prevent heat-related illness. Therefore, we conducted a systematic review to point out values of normal T_{gastrointestinal} measured through ingestible capsules in healthy humans. The study followed PRISMA guidelines and searched the PubMed and Scielo databases from 1971 to 2023. Our search strategy included the descriptors ("gastrointestinal temperature") AND ("measurement"), and eligible studies had to be written in English and measured T_{gastrointestinal} using ingestible capsules or sensors in healthy adults aged 18-59 at rest. Two pairs of researchers independently reviewed titles and abstracts and identified 35 relevant articles out of 1,088 in the initial search. An average value of 37.13 °C with a standard deviation of 0.24 °C was observed, independently of the gender. The values measured ranged from 36.70 °C to 37.69 °C. In conclusion, this systematic review pointed out the mean value of 37.13 ± 0.24 °C measured by ingestible capsules as reference for resting T_{gastrointestinal} in healthy adult individuals.