The operation of metabolism determines species longevity, and in short-lived species this link tends to be highly variable in response to circumstances: exercise, diet, and consequences such as amounts and types of muscle and fat tissue. Longer lived species such as our own are, if anything, remarkable for the comparative lack of variation in life span across large differences in diet and the configuration of muscle and fat in our bodies. As researchers continue to map the interaction of metabolism and aging in laboratory mice, one interesting theme that has emerged is the importance of brown adipose tissue. In the open access paper noted here, the authors report that increasing the proportion of fat tissue that is brown rather than white can produce a 10-15% increase in mouse life span. They suggest this is mediated by SIRT3 activity and downstream effects on mitochondrial function.

The results here might be compared with a very intriguing study published last year in which researchers described what happens to metabolism and fat tissue in mice if their sense of smell is disabled. That resulted in healthier, metabolically superior mice characterized by a greater proportion of brown fat tissue. It built upon a range of past research suggesting that sense of smell plays a sizable role in the metabolic reaction to food. Unfortunately, for these and all other similar metabolic manipulations, we can't expect sizable results to transfer to humans and other long-lived mammals. For those interventions wherein researchers can directly compare mice and humans, the outcome on human life spans is much smaller, and supporting evidence strongly suggests that this holds up across the spectrum of everything involving diet, fat, and metabolism. The health benefits - distinct from effects on the pace of aging - may still be worth pursuing, if the costs are reasonable, however. Consider calorie restriction, for example.

There is also the point that a 10% life span effect in short-lived species is somewhere in the margin of error, and may well be hard to replicate. Looking back at the past few decades, 10% effects come and go in mice. One of the challenges is that an intervention may make mice choose to eat less for any number of reasons. The effects of calorie restriction are so large that they can swamp whatever else is going on in the study. The researchers here report carefully on the details of their many measures of metabolism, but one always has to read those details in order to understand whether they rule out a calorie restriction effect. That may not be the case here, for all that various aspects of the biochemistry under study match up well with what is presently known.

Enhanced longevity and metabolism by brown adipose tissue with disruption of the regulator of G protein signaling 14