Optimal percentage restriction?

[Guest DaveL]

Curious what the literature suggests the optimal % restriction is for humans starting CR in adulthood (to maximize general health and longevity). I've done some searching but haven't found anything definitive or even a strong suggestion. I've read that you shouldn't go above 16% restriction on the CR calculator webpage, but wasn't sure the extent to which that's supported by research - also, that seems very low. Also came across a study that used 25% restriction but it seemed arbitrary.

 

Thanks, Dave

[Michael R]

I've read that you shouldn't go above 16% restriction on the CR calculator webpage

Can you cite and quote this directly? It seems unreasonable ...

 

Also came across a study that used 25% restriction but it seemed arbitrary.

... as it would be. More importantly, here 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."(1)

 

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 thae 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.

 

-Michael

 

Reference

1: Rikke BA, Battaglia ME, Allison DB, Johnson TE. Murine weight loss exhibits significant genetic variation during dietary restriction. Physiol Genomics. 2006 Oct 11;27(2):122-30. Epub 2006 Jul 18. PubMed PMID: 16849633.

[Guest David_K]

Thanks, very informative.

 

That 16% figure I read here:

 

http://www.scientificpsychic.com/health/cron1.html

 

That page has a number of references but didn't see a cite for that figure.

 

I do remember reading at some point that you get maximum health and longevity when using more conservative restriction when starting CR in adulthood, but have no memory of the reference. Additionally even if you're maximizing longevity, you're of course not maximizing health if you're severely restricting calories to the point where you have muscle atrophy etc. - which is why I'm trying to optimize both, and not maximize longevity to the expense of my health.