Active frontiersmen consumed up to 20,000 calories a day to sustain extreme energy expenditures
The claim that active frontiersmen consumed 20,000 calories daily is refuted by physiological research showing that human energy expenditure is strictly capped at much lower levels, even among extreme endurance athletes.
The claim specifies an extraordinarily high daily caloric intake/expenditure (20,000 kcal). Human metabolic limits established in large-scale studies (Pontzer et al., 2019) and measurements of elite athletes (Beis et al., 2024) show that sustained human energy expenditure rarely exceeds ~2.5x to 3x basal metabolic rate (generally peaking under 9,000 kcal/day even in extreme cases). Therefore, the claim is biologically implausible and refuted by the provided literature.
C. Thurber, Lara R. Dugas, C. Ocobock, B. Carlson, J. Speakman, H. Pontzer. Extreme events reveal an alimentary limit on sustained maximal human energy expenditure. 2019. https://doi.org/10.1126/sciadv.aaw0341
This study demonstrates that human sustained energy expenditure has strict physiological limits, capping out at roughly 2.5 times basal metabolic rate over long durations, making claims of 20,000 calories biologically impossible.
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M. Dasa, Olav Aleksander Bu, Ø. Sandbakk, B. Rønnestad, Guy Plasqui, Hilde Gundersen, Morten Kristoffersen. Training volume and total energy expenditure of an Olympic and Ironman world champion: approaching the upper limits of human capabilities.. 2024. https://doi.org/10.1152/japplphysiol.00706.2024
Even extreme world-class endurance athletes peak far below the claimed figure, with measured maximums reaching roughly 7,000 to 8,500 calories per day.
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