Is Body Core Temperature A Core Factor In Obesity?Thursday, October 6, 2011
Yesterday, on my flight back from Orlando, I happened to sit besides Lewis Landsberg, Professor of Medicine and dean emeritus of Chicago’s Northwestern University Feinberg School of Medicine and director of the Northwestern Comprehensive Centre on Obesity, who is certainly well known to anyone working in the fields of hypertension, autonomic nervous system and obesity.
In our conversation, he drew my attention to a paper published in Trans Am Clin Climatol Assoc, in which he discusses the potential importance of the body’s core temperature in weight regulation.
As Landsberg points 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 susbtantially 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 nightie 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
“due to lower basal core temperature set point; greater nocturnal temperature fall; lesser temperature rise during exercise; lesser post-prandial temperature rise; and a greater temperature fall during fasting or decreased energy intake as in therapeutic dieting.”
Given that core temperature can be measured with a precision that far exceeds our ability to measure any other parameter of energy homeostasis, it is perhaps surprising that we still lack a good understanding of the relationship between core temperature and body weight.
As Landsberg points out:
“Studies of body temperature in the obese under different circumstances (exercise, sleeping, after meals) are feasible and may reveal important differences between lean and obese. If this proves to be the case, a new therapeutic target, body temperature, may emerge.”
I would add to this that there also may well be differences in preferred ambient temperatures, which in turn could affect metabolic rate.
It is no secret that some people prefer and can clearly better tolerate lower ambient temperatures than others.
My guess is that people who prefer the cold or can better tolerate it, likely have a well stoked ‘internal combustion engine’ that happily burns plenty of extra calories to maintain core temperature, while those who dislike and are more sensitive to the cold will rather depend on an ‘external combustion engine’ (their home furnace), don more clothing, or simply move to warmer climates in order to expend fewer calories to maintain their core temperatures.
A further layer of complexity (pun intended) is added to this issue by the fact that subcutaneous fat also serves as a most efficient insulator. So, it may well be that obese individuals do in fact have to burn far fewer calories to maintain their core temperatures than the skinny folks, who, I assume will probably be the first to die of cold exposure.
With the Edmonton winter fast approaching it’ll be interesting to see just how much longer I can go without bringing back the woollens and burn off those extra calories I may have brought back from Orlando.
Landsberg L, Young JB, Leonard WR, Linsenmeier RA, & Turek FW (2009). 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, 120, 287-95 PMID: 19768183