Something else to blame on obesity

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In recent decades, residents of affluent Western countries have increasingly

been turning up room temperatures in winter -- a practice that may be

contributing to the obesity epidemic by turning down the body's own

thermostat, researchers suggested.

" Since the 1960s, a cultural shift in norms of thermal comfort and

expectations of 'thermal monotony' have been driven by the widespread uptake

of central heating and air conditioning, " Fiona , MRCPsych, of

University College London, and colleagues wrote online in *Obesity Reviews.*

This reduced exposure to indoor cold may have minimized the need for higher

energy expenditure for the body to stay warm, and co-authors

suggested.

They noted that in the U.K., average living room temperatures rose from

18.3°C (64.94°F) in 1978 to 19.1°C (66.38°F) in 2008 -- and bedroom

temperatures increased from 15.2°C (59.36°F) to 18.5°C (65.3°F).

And while living room temperatures in American households remained stable,

at 21.3°C (70.34°F) between 1987 and 2005, the average bedroom temperature

increased from 19.3°C (66.74°F) to 20.2°C (68.36°F).

and colleagues noted that humans respond to cold through

vasoconstriction and lowering of skin temperatures, by skeletal muscle fiber

contraction leading to shivering, and through adaptive metabolic thermogenic

responses generating heat in tissues.

The low end of the thermoneutral zone of temperature for humans, when

metabolic rate is lowest, is about 25° to 27°C (77° to 80.6°F).

In background material provided by and colleagues, they noted that

studies have shown that energy expenditure is inversely associated with the

ambient thermal environment. Recent research has also helped to explain how

thermogenesis influences energy balance and weight maintenance.

One area of particular interest has been the role of brown fat, previously

thought to have little importance in adult thermogenesis.

" Unlike white adipose tissue, which acts predominantly as an energy storage

depot, [brown adipose tissue] is a thermogenic organ, dissipating energy in

the form of heat, " explained and co-authors.

When brown adipose tissue is activated, it can be detected using positron

emission tomography, and studies have shown that activation -- and the

resulting energy expenditure -- is much more likely to occur in cold

environments.

For instance, and colleagues noted that in one experiment,

decreasing the ambient temperature from 22°C (71.6°F) to 16°C (60.8°F) led

to the detection of brown adipose tissue in almost all healthy volunteers.

The model also suggested that under conditions of full activation of the

brown adipose tissue there would be an increased energy expenditure leading

to a 4 kg (8.82 lb) weight loss over a year, they explained.

Food consumption also can be influenced by thermal conditions.

In both humans and animals, appetite decreases under conditions of warmth,

but in humans food intake is much more influenced by the social environment

and the palatability of food.

Palatability also has been associated with changes in food intake in

animals.

Unlike mice fed a typical low-fat laboratory diet, adjusting their intake to

the ambient temperature, mice fed high-fat diets do not decrease their food

intake at higher temperatures and gain weight.

" These human and animal experimental models suggest that while intake is

somewhat suppressed at higher temperatures, this is unlikely to fully

compensate for the reduced energy expenditure of a warm environment

particularly where highly palatable foods are available, " and

colleagues observed.

This research argues in favor of a causal link between increased time spent

in thermal comfort and weight gain in the population, they said.

" Establishing the significance and magnitude of the effects of both

short-term and long-term thermal exposures on body weight could lead to the

development of novel therapies to address obesity on an individual and a

population level, " they concluded.

*Primary source: *Obesity Reviews

Source reference:

F, et al " Could increased time spent in a thermal comfort zone

contribute to population increases in obesity? " *Obesity Rev* 2011; DOI:

10.1111/j.1467-789X.2010.00851.x.<http://onlinelibrary.wiley.com/doi/10.1111/j.1\

467-789X.2010.00851.x/abstract>

--

Ortiz, MS, RD

*The FRUGAL Dietitian* <http://www.thefrugaldietitian.com>

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