Dr. Stephan Guyenet thinks they might. It’s not so much heat as it is failing to expose our bodies adequately to temperatures around 60° F (15.6° C) or lower on a regular basis. Here’s a human experiment Dr. G wrote about:
The second study went further, using a longer cold exposure protocol to investigate changes in fat mass among people with low brown fat activity at baseline (4). Researchers exposed volunteers to 63 F (17 C) air for two hours a day over a six-week period; again I assume they were lightly clothed. As in the previous study, they observed an increase in brown fat activity with cold training, and they found that calorie expenditure was higher when subjects were in the ‘cold’ air. After six weeks of training, body fat mass had declined by about 5 percent. This is despite the fact that all subjects were lean to begin with!
I thought this study tied in with that one showing an inverse relationship between altitude and obesity. Environmental temperature rises roughly 3° F with every 1,000 feet (305 meters). But the altitude study controlled for (accounted for) temperature, meaning that the temperature had nothing to do with the association.
Somebody’s probably already tried to link environmental temperatures—whether inside the house or out—to obesity rates. Let me know if you find it.
PS: A few minutes at Pubmed.gov revealed this 2013 abstract:
Objective: Raised ambient temperatures may result in a negative energy balance characterized by decreased food intake and raised energy expenditure. This study tested whether indoor temperatures above the thermoneutral zone for clothed humans (approx. 23 o C) were associated with a reduced body mass index (BMI). Design and Methods: Participants were 100,152 adults (≥ 16 years) drawn from 13 consecutive annual waves of the nationally representative Health Survey for England (1995 – 2007). Results: BMI levels of those residing in air temperatures above 23 o C were lower than those living in an ambient temperature of under 19 o C (b = -.233, SE =.053, p <.001), in analyses that adjusted for participant age, gender, social class, health and the month/year of assessment. Robustness tests showed that high indoor temperatures were associated with reduced BMI levels in winter and non-winter months and early (1995 – 2000) and later (2001 – 2007) survey waves. Including additional demographic, environmental, and health behavior variables did not diminish the link between high indoor temperatures and reduced BMI. Conclusions: Elevated ambient indoor temperatures are associated with low BMI levels. Further research is needed to establish the potential causal nature of this relationship.
PPS: And there’s this abstract, probably from the altitude study I mentioned:
“There was an approximately parabolic relationship between mean annual temperature and obesity, with maximum prevalence in counties with average temperatures near 18 °C [64.4° F].”
I don’t have the full article, but parabolic, to me in this context, probably means the obesity incidence was highest at 64.4° F, with lower obesity incidence both above and below 64.4°.
Of course, living in a particular environment doesn’t equate to exposing yourself to outdoor temperatures. But it makes sense that someone living in a cold environment will have more cold exposure than someone in a hot climate.
Perhaps 64.4° F is a sweet spot for efficient body temp regulation and energy partitioning. Living at temps significantly above or below that may cost you energy-wise: you expend extra calories maintaining a normal body temperature, tending to result in lower obesity incidence.
I think brown fat and thermogenesis are fun to study and read about, but I don’t think they can be used in any meaningful way to manipulate one’s leanness and health.
There are too many internal mechanisms to counter changes in temperature. You mentioned a few (too hot, eat less). But there are many more subtle changes that occur. Cold down-regulates thyroid, so do low light levels, both common winter phenomenon–look into ‘Polar T3 Syndrome’. Prolonged cold exposure favors subcutaneous fat growth. Ever see a skinny walrus?
Also, BAT is such a fickle thing. Not everyone has BAT, so doing things to grow your BAT may be a colossal waste of time. You’d need a CAT/PET scan to determine if you were doing it right.
I think that everyone should get exposure to seasonal temperatures as well as as much natural daylight as possible. We should also mind circadian rhythms (shut of computer at 9!). These things will ensure adequate BAT–who’s main effect is circumventing the Kreb’s Cycle and burning calories as waste heat–as much, or more than prolonged, forced exposure to cold.
Tim, thanks for that contribution.