A group of specialized neurons located at the floor of the brain acts as a “thermostat” and keeps the “core temperature” of most humans within several degrees of 37 degrees C. (or 98.6 degrees F.). Hyperthermic sessions can easily raise the core temperature of a user from 2 to 4 degrees F. (or 1 to 2.5 degrees C.) depending on the duration of the session, the temperature setting, and the heat acclimation status of the user. A rise in core temperature triggers the body’s temperature regulating center for heat dissipation. Numerous studies have shown that exercise in hot, dry environments is limited by the attainment of a critical level of core temperature and that high core temperature, as opposed to circulatory failure or metabolic depletion. Core temperature has emerged as the critical factor in heat stress.
Research shows that higher core body temperatures appear to increase metabolism. A review published in 2009 in Transactions of the American Clinical and Climatological Association1 reports that an increase in body temperature is associated with a higher metabolic rate, and higher body temperatures do speed up metabolism. For each degree Celsius the body temperature rises, the metabolism increases by 10 to 13 percent . This means that a person will expend an extra 100 to 130 calories per day if they normally eat 2,000 calories daily because body temperature accounts for about 50 percent of energy expenditure.
Cooler core body temperatures appear to lower metabolic rates. The review published in 2009 in Transactions of the American Clinical and Climatological Association notes that a 1 degree Celsius drop in body temperature decreases metabolism and results in the expenditure of about 100 to 130 fewer calories each day.
Does Outside Air Temperature Matter?
While a warmer body temperature does tend to increase metabolism, cooler air temperatures may also boost metabolism. According to the National Institutes of Health, men exposed to cooler air temperatures showed increases in brown body fat and higher metabolisms in a 2014 study published in Diabetes. A study published in 2014 in Plos One also found that energy expenditure is higher during exposure to cold temperatures, and cold exposure significantly increases metabolism in mice.
What about Exercise?
Exercise causes an elevation in body temperature and an increased metabolism during physical activity. In fact, muscle has a higher metabolic rate than body fat, so the more muscle mass you gain by exercising, the higher your metabolism will be, even during periods of rest. Exercising in hot weather burns more calories than working out in cold temperatures because it takes more energy to cool your body in the heat, reports the American Council on Exercise (ACE). An exception is if you’re shivering. ACE notes that shivering can cause you to expend 400 calories in just one hour.
As Landsberg has pointed out, maintenance of the body’s core temperature (at around 37 degrees centigrade) accounts for almost 50% of total energy expenditure, far more than physical activity or adaptive thermogenesis (which each account for roughly 10% of total energy expenditure in today’s largely sedentary individuals). Thus, even small differences in core temperature or in the number of calories required to sustain homeothermy, can account for a substantial differences in caloric output and thus body weight both between and within individuals.
Landsberg emphasizes the potential role that differences in the ability to maintain and defend core body temperature may play in weight gain. For example, it is well known that even a small rise in core temperature can substantially alter metabolic rate – each degree C rise in temperature is associated with a 10-13% increase in oxygen consumption. Furthermore, both metabolic rate and core temperature varies substantially amongst individuals and populations and, perhaps not unexpectedly, there is a clear inverse relationship between mean annual ambient temperature and resting metabolic rate in different geographic regions – higher in the arctic and lower in the tropics. As regular readers will recall, small differences in the amount of thermogenic brown adipose tissue (which can be stimulated by cold exposure) can account for 100s of extra calories burnt each day.
Landsberg also points out that a fall in temperature is an important part of the adaptive response to energy deprivation (as in dieting). Interestingly it appears that some people may also experience an exaggeration of the normal fall in core temperature (and therefore burn fewer calories) during sleep. Although current data is far from conclusive, it could well be that obese individuals may burn far fewer calories than their non-obese counterparts
A 2013 study (Kozhevnikov M, Elliott J, Shephard J, Gramann K., Neurocognitive and Somatic Components of Temperature Increases during g-Tummo Meditation: Legend and Reality3, suggests that a biological inability to create sufficient core body heat—evidence of a thermogenic handicap—is associated with obesity and may be linked to the obesity epidemic. The findings indicate that there are two factors affecting temperature increase. The first is the somatic component which causes thermogenesis, while the second is the neurocognitive component (meditative visualization) that aids in sustaining temperature increases for longer periods. Without meditative visualization, both meditators and non-meditators were capable of using the Forceful Breath vase breathing only for a limited time, resulting in limited temperature increases in the range of normal body temperature. Overall, the results suggest that specific aspects of the g-tummo technique might help non-meditators learn how to regulate their body temperature, which has implications for improving health and regulating cognitive performance.
1 Landsberg L, Young JB, Leonard WR, Linsenmeier RA, Turek FW. Do the Obese Have Lower Body Temperatures? A New Look at a Forgotten Variable in Energy Balance. Transactions of the American Clinical and Climatological Association. 2009;120:287-295.
2 Effect of intermittent cold exposure on brown fat activation, obesity, and energy homeostasis in mice, Ravussin Y1, Xiao C1, Gavrilova O2, Reitman ML1, PLoS One. 2014 Jan 17;9(1):e85876. doi: 10.1371/journal.pone.0085876. eCollection 2014.
3Neurocognitive and somatic components of temperature increases during g-tummo meditation: legend and reality, Kozhevnikov M1, Elliott J, Shephard J, Gramann K., PLoS One. 2013;8(3):e58244. doi: 10.1371/journal.pone.0058244. Epub 2013 Mar 29.
APL (American Performance Labs) is a research group dedicated to the collection, analysis, and dissemination of published research and articles on the science of hyperthermia and the various applications, technologies and protocols for the use of hyperthermic conditioning.