Bradycardia is one of the common cardiac abnormalities in patients with eating disorders. It ensues from hypometabolism, which results from reduced caloric intake and consequential weight loss. Hypothermia is another consequence of hypometabolism. While at-rest metabolism and body mass index (BMI) are typically used to assess hypometabolism and estimate potential bradycardia, we hypothesised that body temperature, which is easy to measure, could also capture the presence of this threatening cardiovascular condition. We monitored heart rate continuously for 72 h, measured resting energy expenditure (REE) and assessed body temperature in 12 body parts for 58 patients with anorexia nervosa (AN) and 29 patients with bulimia nervosa (BN). Palm temperature reflects bradycardia in both AN and BN, explaining 18% of its variance (p < 0.001), capturing this aspect even more efficiently than BMI. We also observe different correlations between palm temperature, abdominal temperature, BMI, REE and levels of physical activity. Palm temperature could be used as a warning of bradycardia, a serious cardiovascular condition which can be difficult to detect in short visits with outpatients. Further studies are needed to determine how useful bradycardia and palm temperature could be to assess severity and prognosis of the disorder.