Having the central heating on may be contributing to our ballooning waistlines, Dutch researchers suggest.
They say higher temperatures in homes, offices and hospitals provide more comfort, but mean bodies no longer need to burn extra calories to keep warm.
A Maastricht University Medical Centre group says 19C (66F) is sufficient to provide the right balance.
However, some argue that turning down the thermostat would merely prompt people to eat more.
The weight loss idea, proposed in Trends in Endocrinology and Metabolism, comes down to energy balance.
People will gain weight if they consume more calories in food than they burn off in day-to-day life.
Cooler and thinner?
The report said people spent 90% of their time indoors and yet "we cool and heat our dwellings for maximal comfort while minimising our body energy expenditure necessary to control body temperatures".
The energy balance is shifted towards weight gain and can require a drop in temperature to help burn off some calories.
Dr Wouter van Marken Lichtenbelt told the BBC: "19C is enough - and not for the whole day.
"Energy increases were in the order of 6% in mild cold, and in the long term that could really make a difference.
"It could be a substantial influence and help in combination with food changes and exercise."
He said people could "try turning the thermostat down" at home or "go outside".
About two in every three adults in the UK are classed as overweight or obese, and it is a growing problem globally.
Cases have quadrupled to about one billion in the developing world since 1980.
However, temperature control may not be the perfect solution and is the source of some debate.
Dr Michael Daly, who investigated the issue at the University of Stirling, told BBC News: "If you didn't compensate you would lose weight, but that's not really how it happens. You will want a chocolate bar."
"Also, studies suggest that in cold indoor temperatures you are more likely to get a stroke, and there is a [overall] winter mortality effect."
His research on 100,000 homes in England suggested people in houses heated above 23C tended to be slightly thinner, because at this point the body needed to lose heat - and sweating used up energy.
He said higher temperatures also lowered appetite and the amount of food being consumed.
Tam Fry, from the UK's National Obesity Forum, argued: "A cold environment switches on brown fat deposits, which are said to generate 300 times more heat than any organ in the body.
"They are its natural thermal resource. The heat kept us warm as babies and is still capable of keeping us warm now.
"Losing weight at the same time is a bonus. Turn your stat down now and see for yourself."