BMI and longevity revisited

[Guest guest]

I thought the older epidemiological studies

showing a BMI of about 23 as correlated with

longevity were flawed because the low end was

polluted by those that choose to smoke in order

to lose weight? Was not the optimal BMI lower

than 23 when only non-smokers were considered?

Does anyone have this info? I cannot remember

where I read that a while back.

[Guest guest]

You will forgive me if I sound impatient but this is in our files. The folder " CRON SCIENCE " lists a file called " Extreme CRON vs Moderate CRON " . In that extensive file are posts that discuss BMI. One of those points to this post by Jeff:

/message/14089

in which smoking and other risks were factored into the results.

on 10/5/2006 6:19 PM, orb85750 at sudarsky@... wrote:

I thought the older epidemiological studies

showing a BMI of about 23 as correlated with

longevity were flawed because the low end was

polluted by those that choose to smoke in order

to lose weight? Was not the optimal BMI lower

than 23 when only non-smokers were considered?

Does anyone have this info? I cannot remember

where I read that a while back.

[Guest guest]

Hi Orb:

I don't believe the final unequivocal study has been done yet that

definitively decided this issue. Of course this is true of so many

aspects of health research.

There are many reasons why a study might find that the people with a

lower BMI might live less long, none of which would detract from the

desirability of CRON. A few that immediately come to mind are listed

below. Doubtless there are others.

1. Smoking, as you point out.

2. Anorexia.

3. Having a low appetite because of a subclinical illness, which may

not produce overt symptoms for years.

4. Eating a small number of calories, not paying attention to *ON*

and suffering life-long nutrient deficiencies.

5. The 'can-eat-all-they-want-and-never-put-on-weight' syndrome, the

only logical explanation I can think of for which is serious

intestinal absorption problems (or sleep-running marathons without any

recollection of it?) also resulting in nutrient deficiencies, and

probably other problems as well.

There is an additional, very fundamental, and important difference

which may largely explain why the studies in humans may sometimes seem

to give different results from those in mice and monkeys. In the case

of animal experiments the subjects themselves do not choose whether to

be restricted. They are randomly allocated at the outset either to

the control group or the experimental group with the intention that

the two groups start out as nearly as possible identical.

But in SURVEYS of lean and overweight people it is as if they looked

at 1000 mice, did nothing at the outset to randomize them, and then

looked at the lifespan of them according to whether they

are 'naturally' (perhaps often for reasons that are far from natural,

and unhealthy) slim or overweight. The people unknowingly in effect

selected themselves based often on whether they have a large or poor

appetite. So there is no control group, which, clearly, is a pretty

major deficiency by the standards of serious research these days. And

people with a poor appetite may be less healthy, imo.

So that study was not a study of caloric restriction, but of an

altogether different phenomenon - the lifespans of 'naturally' slim or

higher weight individuals.

In the WUSTL study the subjects also selected themselves. But they

didn't select themselves based on what their final weight might be if

they didn't restrict. They had selected themselves because of a

determination to preserve their health.

I believe the study you may be thinking of found people with a BMI of

27 had the longest life expectancy! These I submit are people who

have a good appetite and were able to restrict themslves enough to not

become obese. Comparatively healthy people. But they would have

lived a lot longer if they had restricted their calories a lot more.

We do know what happens to the biomarkers of people when they restrict

their calories despite the fact they would much prefer to eat more,

and pay close attention to food quality. It doesn't seem likely that

the CRON biomarkers would be so good but the outcome worse.

Hope this helps.

Rodney.

>

> I thought the older epidemiological studies

> showing a BMI of about 23 as correlated with

> longevity were flawed because the low end was

> polluted by those that choose to smoke in order

> to lose weight? Was not the optimal BMI lower

> than 23 when only non-smokers were considered?

> Does anyone have this info? I cannot remember

> where I read that a while back.

>