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[Admin Note: This is a series of posts originally on another thread that started on the topic of how cold exposure can have beneficial effects for health and longevity despite increasing calorie expenditure. I debated where to move them, since they seem to fit General Health & Longevity, CR Practice, and CR Science. I finally opted for CR Science, since you'll see if you haven't been reading them already, they bear directly on CR and CR mimetics. If anyone feels strongly this was the wrong choice, I'll be happy to move the thread to another forum. --Dean] Rodney, Whenever I see someone use the word "surely", I figure the writer isn't very sure about, or doesn't have real evidence to support, what they are about to say. I'm guilty of it sometimes myself. People's appetites differ for a lot of reasons, many of them without negative health implications. Genetics is one example that can alter metabolic rate and therefore hunger (remember the ob/ob mice who ate more but didn't live shorter lives). Exercise or exposure to cold (and extra brown fat that cold exposure can create/promote) will increase calorie expenditure without detrimental effects. In fact, perhaps my favorite study of all time (except for the suffering of the animals involved) was the famous "rats with cold feet" study  by John Holloszy. Holloszy found that rats who lived their lives standing in a cold puddle of water ate 44% more than normally-housed rats, but nonetheless stayed thin and didn't live any shorter lives than the normally-housed rats. In fact they lived slightly longer and got less cancer. Our friend Josh Mitteldorf did a whole blog post about the hormetic benefits of cold exposure, and how it casts serious doubt (if not debunks) the popular "rate of living" theory of aging. --Dean (who composed this post while pedalling shirtless and wearing just bike shorts on his stationary bike in his 59 degF basement to maximize hormesis... ) --------  J Appl Physiol (1985). 1986 Nov;61(5):1656-60. Longevity of cold-exposed rats: a reevaluation of the "rate-of-living theory". Holloszy JO, Smith EK. It has been postulated that increased energy expenditure results in shortened survival. To test this "rate-of-living theory" we examined the effect of raising energy expenditure by means of cold exposure on the longevity of rats. Male 6-mo-old SPF Long-Evans rats were gradually accustomed to immersion in cool water (23 degrees C). After 3 mo they were standing in the cool water for 4 h/day, 5 days/wk. They were maintained on this program until age 32 mo. The cold exposure resulted in a 44% increase in food intake (P less than 0.001). Despite their greater food intake, the cold-exposed rats' body weights were significantly lower than those of control animals from age 11 to 32 mo. The average age at death of the cold-exposed rats was 968 +/- 141 days compared with 923 +/- 159 days for the controls. The cold exposure appeared to protect against neoplasia, particularly sarcomas; only 24% of the necropsied cold-exposed rats had malignancies compared with 57% for the controls. The results of this study provide no support for the concept that increased energy expenditure decreases longevity. PMID: 3781978 [PubMed - indexed for MEDLINE]