If you want to lose weight, the calculation is deceptively simple: burn more calories than you consume. Of course for many people this is much easier said than done--to the tune of an $82 billion health and fitness industry.
Sometimes people can't find the time to exercise, or they find that it just doesn't seem to work for them. It can be highly frustrating.
Now, however there's preliminary research that suggests there might be a non-exercise alternative that people can do to burn calories. In fact, it seems almost too good to be true: "passive heating for human health."
Take a hot bath
Writing in The Conversation, Dr. Steve Faulkner of Longborough University in the United Kingdom recounted a recent experiment in which he and his colleagues recruited 14 men, and assigned them either to work out for an hour each day (cycling), or in the alternative, simply to take an hour long soak in a hot bath.
While many cultures around the world have extolled the benefits of taking hot baths and saunas, Faulkner writes, it's only in the last few years that scientists have explored whether there is a physiological reason.
Result? In Faulkner's study, at least, they found that:
"Cycling resulted in more calories being burned compared with a hot bath, but bathing resulted in about as many calories being burned as a half-hour walk (around 140 calories). The overall blood sugar response to both conditions was similar, but peak blood sugar after eating was about 10% lower when participants took a hot bath compared with when they exercised."
The specifics of the hot bath seem important here; Faulkner writes that the men in the study soaked in water that was heated to 40 degrees Celsius (about 104 Fahrenheit).
Or, perhaps, a sauna
The results seem in line with other studies, too.
For example, in 2015 a Finnish study found that "frequent saunas can reduce the risk of having a heart attack or stroke - at least in men," Faulkner writes, and another study at the University of Oregon found that "regular hot baths can lower blood pressure."
Beyond simply burning calories, there appear to be other health benefits too, including better control of blood sugar,
But you should probably still exercise
The science behind these intriguing findings has to do with something called heat shock proteins: "molecules that are made by all cells of the human body in response to stresses."
Regardless of whether you're working out at the gym or taking a hot bath, Faulkner explains, the body seems to create more of these kinds of molecules, which "may help the function of insulin and improve blood sugar control."
Certainly, nobody is suggesting that people abandon diet and quit working out, and instead simply sit in the tub. But, the hope is that further research into passive heating could result in real benefits and an "alternative to exercise" for people who don't have any other option.