you burn fat tissue. >> reporter: ferriss is not alone. a friend introduced him to ray cronise, who says it changed his life, too. >> we can use the thermal environment to super charge our weight loss. >> reporter: struggling with his weight, ray took a scientific approach. >> when i realized that running a marathon only burned 2,600 calories, i was pretty disenchanted at that point. >> reporter: until he heard something that sounded impossible. olympic swimmer michael phelps' diet of 12,000 call reap as day, the same amount ray consumed in a whole week. >> if most people hear that michael eats that much food they think he's an olympic athlete, of course he eats that much food. but it's way out of proportion. then, it occurred to me michael spends most of the time in the water, and water is 24 times more thermally conductive than air. what that means is water is sucking that energy and heat out of his body. his body was burning excess calories just to maintain his body temperature. >> reporter: he dug deeper and found that for years, nasa

author tim ferriss says the body has to work overtime to overcome the cold. >> the body wants to maintain, a homeostasis. so, 98.6 degrees. if you make it cold, it will do whatever it can to get back to 98.6. it burns calories to do that. >> reporter: what is going on in your body? >> there's a type of fat called brown adipose tissue. cold can trigger this. it produces fat and you burn fat tissue. >> reporter: his advice is backed by real science. >> we can use the thermal environment to super charge the weight loss. >> reporter: ray kron neez investigated the effects of temperature on astronauts. >> some of these people saw metabolism rates boost by as much as 20%. >> reporter: he had been struggling to lose weight with diet and exercise. >> you get that 12 weeks into it and you hit a wall and you really want to give up. >> reporter: adding a thermal element, he tripled the rate of weight loss, going from this to this, losing 30 pounds in six weeks. but this isn't for everyone, and there's a risk of doing more harm than good. so, he says, always carry a coat and start off small. >> seven

author tim ferriss says the body has to work overtime to overcome the cold. >> the body wants to maintain, 98.6 degrees. and if you make it cold, it will do everything it can to get back to 98.6. and it burns calories to do that. heat equals calories. >> reporter: what is going on in your body? >> there's actually a type of fat called brown adipose tissue. b.a.t. cold can trigger this b.a.t., it actually produces heat and you burn fat tissue. >> reporter: his advice is backed by real science. >> we can use the thermal environment to supercharge our weight loss. >> reporter: cray cronise a former nasa scientist, investigated the effects of temperature on astronauts. >> in environments as mild as 60 degrees, some of these people saw metabolism rates boost by as much as 20%. >> reporter: cronise had been struggling to lose weight with diet and exercise. adding a thermal element, he tripled the rate of weight loss. going from this to this, losing 30 pounds in 6, short weeks. he says smaller actions like turning down the thermostat and drinking ice water can boost the metabolism and are a lot

author tim ferriss says the body has to work overtime to overcome the cold. >> the body wants to maintaina homeostasis. if you make it cold it will do everything it can to get to 98.6. and it has to burn calories to do that. heat equals calories. >> what is going on in your body? >> there's actually a type of fat called brown adipose tissue, b.a.t. cold can trigger this b.a.t., that actually produces heat, and you burn fat tissue. >> reporter: his advice is backed by real science. >> we can use the thermal environment to super-charge our weight loss. >> reporter: ray cronis, former nasa scientist, investigated the effects of temperature on astronauts. >> in environments as mild as 60 degrees, some of these people saw metabolism rates boost by as much as 20%. >> reporter: he'd been struggling to lose weight with diet and exercise. adding a thermal element he tripled the rate of weight loss, going from this to this, losing 30 pounds in six short weeks. but ice baths and shiver walks aren't for everyone, and there's a risk of doing more harm than good. he says always carry a coat and start o