Body temperature and pulse

Body temperature and pulse are the primary, cost-free indicators Ray Peat used to assess the underlying metabolic rate, arguing they reveal more about physiological energy production than standard thyroid lab tests. 2 Peat built upon the work of Broda Barnes, who identified that a waking axillary temperature below 97.8°F and a failure to rise to approximately 98.6°F during the day suggested hypothyroidism. 2 However, Peat observed that environmental factors like a hot, humid climate could artificially normalize the temperature of even severely hypothyroid individuals, leading him to insist that pulse rate must be measured concurrently to avoid being misled. 2 He noted that a low metabolizing person given environmental support might maintain a normal temperature while their pulse remained pathologically low, sometimes between 45 and 65 beats per minute. 2

The interpretation of these metrics hinges on distinguishing thyroid-driven metabolism from compensatory stress responses. Peat documented that individuals in an exhausted hypothyroid state often have a low temperature and pulse, but those who shift into a manic or highly stressed phase can wake with a normal temperature and a pulse of 80 due to high levels of adrenaline and cortisol. 2 A critical diagnostic pattern he identified is the postprandial temperature drop: if a person’s temperature and pulse fall significantly after eating a carbohydrate-rich breakfast, it reveals that their apparent metabolic rate was being artificially propped up by emergency stress hormones, which food temporarily reduces. 2 Danny Roddy has elaborated on this, noting that a combination of a slightly lower core temperature with a high pulse rate is indicative of high adrenaline and cortisol compensating for low thyroid function, whereas a high temperature and high pulse accompanied by a feeling of relaxation signals genuine thyroid-driven metabolism. 2

Peat considered a resting pulse rate of 80 to 85 beats per minute as optimal for a healthy young person, a state achieved when TSH and parathyroid hormone are both at the bottom of their reference ranges, indicating cells are autonomously running at a high energy level. 4 He cautioned that a low resting heart rate, often culturally misconstrued as a sign of fitness, is frequently associated with a down-regulated metabolism, low testosterone, increased estrogen, and degenerative problems. 2 Roddy reinforces that tracking these metrics upon waking and in the afternoon leverages the thyroid’s circadian rhythm—where function should be lowest in the morning and highest in the afternoon—to provide a relative sense of thyroid status, emphasizing that temperature and pulse don't lie in the way that lab work, which he compares to an interpretive painting, can be wildly misread. 2

Practical measurement requires attention to confounding variables. Peat noted that in overweight individuals, subcutaneous fat can insulate the body so thoroughly that it takes hours for an axillary thermometer to reflect core temperature, and that the vasoconstrictive effects of adrenaline can keep the skin, fingers, and toes cold even when core temperature appears normal. 2 He therefore considered the temperature of the extremities in a cool room a more sensitive indicator than core readings alone. 7 Ultimately, Peat viewed body temperature as merely a rough approximation of how much fuel is being burned, stating that the definitive metabolic test would be the direct measurement of oxygen consumption and carbon dioxide production, as was done with 1930s basal metabolic rate assessments. 7 The Achilles reflex relaxation test—where a healthy thyroid function produces an instantaneous, floppy relaxation of the foot after a tendon tap—served as another quick, corroborating physical indicator. 2