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Old Mon, Aug-05-19, 06:19
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teaser teaser is offline
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Posts: 14,041
Plan: mostly milkfat
Stats: 190/152.4/154 Male 67inches
Progress: 104%
Location: Ontario

Probably talking about the David Ludwig studies where already reduced weight people had higher metabolic rates on a low carb versus a high carb diet.

I'm not sure about hummingbirds.. but

Metabolism is a defining feature of all living organisms, with the metabolic process resulting in the production of free radicals that can cause permanent damage to DNA and other molecules. Surprisingly, birds, bats and other organisms with high metabolic rates have some of the slowest rates of senescence begging the question whether species with high metabolic rates also have evolved mechanisms to cope with damage induced by metabolism. To test whether species with the highest metabolic rates also lived the longest I determined the relationship between relative longevity (maximum lifespan), after adjusting for annual adult survival rate, body mass and sampling effort, and mass‐specific field metabolic rate (FMR) in 35 species of birds. There was a strongly positive relationship between relative longevity and FMR, consistent with the hypothesis. This conclusion was robust to statistical control for effects of potentially confounding variables such as age at first reproduction, latitude and migration distance, and similarity in phenotype among species because of common phylogenetic descent. Therefore, species of birds with high metabolic rates senesce more slowly than species with low metabolic rates.

With their small size and high metabolism, the hummingbird lifespan is generally only a few years, but the life expectancy of a hummingbird is variable and some have survived for more than a decade. The oldest known wild hummingbird lived to 12 years and 2 months. In captive environments such as zoos, with proper feeding and nutrition, hummingbirds can live up to 14 years. In the wild, they spend their lives in a fast-paced migratory search for food.

I would guess the main problem for wild hummingbird longevity is probably that they're bite-sized.

Only one study on ketogenic diet and longevity, in mice.

A ketogenic diet extends longevity and healthspan in adult mice

Metabolic rate doesn't seem to be addressed directly--but on equal calories, the mice had a lower body weight and lower body fat than control mice--so either a higher metabolic rate, or decreased calorie (fat) absorption or ketone wasting or something. I'd guess they were just burning more fat. They also had higher muscle mass and did better in the gym (hanging time, grip strength, time to complete a run).

Whoops--metabolic rate is addressed in the supplemental material. 2 kJ per hour for ketogenic versus 1.88 per hour for the control mice.

But 'add a lot of fat?' I'd rather say replace a lot of calories (especially carbohydrate) with fat. Instead of, rather than in addition to, is what makes a diet ketogenic.
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