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[A1CR]

MR reigns in...

A CRONie wrote:

> From: MR

>> The only real problem is the mistaken use of one's PRESENT body weight
>> maintenance requirements, and thus BMR, using a simplified
>> Harris-Benedict equation, to calculate "%CR" -- a mistake that is
>> unfortunately promulgated on the [CR Society] List, too.

> Just as unfortunately, despite requests for such from
> the promulgator(s), alternatives have rarely been offered.

That's because there are no valid ways of doing it in humans,
unfortunately. In mice, %CR is determined by taking a highly
genetically
homogeneous cohort of mice, monitoring their literally ad
libitum food
intake of a completely consistent diet, and cutting this
back by 10-20%
to avoid the confounding effects of obesity -- this
restricted food
intake is stipulated as "AL." CR is then determined by a
cutback from
that level.

You can't do the same thing in humans, because we don't have a
genetically homogeneous stock from which to work, the
individuals reach
their adult body weights and the compartmentalization of
same quite
differently, and the diets consumed by different people vary
significantly much (we know that different diets with the same
ostensible Caloric content contain differing amounts of
actual available
energy).

"during dietary restriction (DR) for [mouse] females eating
60% ad
libitum (AL)[,] 5 cohorts across 81 different strains (22
strains tested
twice)[,] ... Weight loss exhibited highly significant genetic
variation, with DR body weights ranging from approximately
60 to
approximately 85% of AL body weight. This variation was not
explained by
the strain differences in absolute food intake, feces
calorie content,
motor activity, or AL body fat."

Thus, to go by maintenance requirements of weights thus
established,
thru' BMR via Harris-Benedict, and set that as %CR is to
engage in a
petitio principii.

It's hard to see what that benefit of having this data would
be even if
we knew it. We don't yet even know if CR works in humans,
for goodness'
sake; how directly the rodent results will extrapolate to
humans as a
given %CR is an even remoter question.

Suppose that you knew your %CR. How would your behavior be
changed? I am
quite confident that no one is as CRed as would provide
MAXIMUM life
extension benefits, since from rodent evidence the benefits
extend
linearly as an inverse proportion of Caloric intake right
down to the
point of starvation; I don't believe that anyone would be
able to
tolerate the fullest extent of survivable CR on a voluntary
basis (cf
rodent females cannibalizing their young, eg).

If you're already doing as much CR as you find tolerable,
knowing that
you're "only" 30% CRed is not going to force anyone further.
If you
could find more CR tolerable, then tautologically you aren't
as CRed as
you could be, and if LE is your goal you would be looking at
more CR
IAC, whether you're at 10% or 40% CR.

In short, it's an operational impossibility and a practical
irrelevance
to put forward a number; people should stop wasting their
efforts in
worrying about it, and get on with weighing their broccoli and
monitoring their zinc-to-copper ratios.

-MR [reposted on behalf of MR]