Mild cold stress naturally lowers the respiratory quotient (RQ), shifting substrate utilization toward fat oxidation.
"it turns out mild cold stress naturally tends to lower your RQ, meaning shifting towards fat." (said at 0:32:23)
Mild cold exposure (above the shivering threshold) can promote lipid utilization and non-shivering thermogenesis mediated by brown adipose tissue and skeletal muscle, and changes in thermoregulatory mediators like irisin correlate with lower respiratory quotient (RQ) and higher fat oxidation. However, whole-body indirect calorimetry studies indicate that this shift is not universal: controlled 24-hour trials of mild cold (e.g., 19 °C) found no significant overall decrease in 24-hour respiratory exchange ratio (RER) across all participants, and cold-induced metabolic flexibility varies considerably by ethnicity and individual metabolic status. Furthermore, if cold stress becomes severe enough to induce shivering, substrate utilization shifts heavily toward carbohydrate oxidation rather than fat oxidation.
- supports: The potential role of irisin in the thermoregulatory responses to mild cold exposure in ad… (American journal of human biology : the official journal of the Human Biology Council 2016)
"Adjusted for age, gender, insulin sensitivity, and body composition, fold changes in irisin were inversely related to respiratory quotient (r= -0.54, P = 0.048)... Greater irisin was related to a greater fasting fat oxidation in the absence of shivering." (abstract, results and conclusions)
pubmedfull study (doi) - context: Cold induces increased ad libitum energy intake independent of changes in energy expenditu… (The American journal of clinical nutrition 2025)
"Neither eucaloric EE, RER, nor carbohydrate oxidation (CARBOX) was significantly changed by cold exposure." (abstract, results, passage verified)
pubmedfull study (doi) - context: Cold-induced metabolic flexibility explains ethnic disparities among individuals with obes… (International journal of obesity (2005) 2026)
"Chinese participants had greater increase in energy expenditure and a more pronounced fuel switch (RER, COX and FOX) with cold. For Chinese individuals, better cold-induced MetF was independently associated with lower fasting insulin and insulin resistance... This association was not observed in Asian Indians." (abstract, results, passage verified)
pubmedfull study (doi)