Weight loss stalled

[Sibiriak]

So a condition where an high BMI is not due to adiposity but to muscle mass cannot be part of the conceptual framework, since BMI is no more a proxy for adiposity, rather becomes a proxy for muscle mass.

 

Bottom line, the observation that the nadir of mortality hazard lies in an area of 22-25 BMI (depending on follow up times) is, according to logic reasoning, not applicable to individuals with well developed muscle mass.

 

 

That would be strictly true only if it is adiposity alone and not calories  (as well) which is the causal link between BMI and mortality.   No?

[mccoy]

Sibiriak,

 

So a condition where an high BMI is not due to adiposity but to muscle mass cannot be part of the conceptual framework, since BMI is no more a proxy for adiposity, rather becomes a proxy for muscle mass.

 

Bottom line, the observation that the nadir of mortality hazard lies in an area of 22-25 BMI (depending on follow up times) is, according to logic reasoning, not applicable to individuals with well developed muscle mass.

 

 

That would be strictly true only if it is adiposity alone and not calories  (as well) which is the causal link between BMI and mortality.   No?

It is not exactly the same. Adiposity is a result, a systemic state observed after the metabolic processes. Whereas ingested calories is energy which is transformed according to metabolism.it can become fat, muscle bone or excreta. Where cr and exercise are concerned I take it we have data on lab rats but not on humans.

Bottom line, researchers seem to correlate bmi to adiposity and not to calories. The latter would bring about a greater variability and uncertainty in the results since calories are not always turned to fat.

[Sibiriak]

since calories are not always turned to fat.

 

That's the point.   How do we know that it is excess fat entirely (one particular result of excess calories),  and not excess calories per se (as well),  that is the causal link between BMI and mortality?

 

It could be that higher calorie intake in and of itself (regardless of whether it is turned to fat or muscle, is burned off through exercise etc.) has a negative impact on longevity.

 

is, according to logic reasoning, not applicable

 

My point is that I'm not sure  you can draw the "not applicable" conclusion strictly by logic.   There's no purely logical reason that excess calories in and of themselves could not have at least some negative impact on longevity (even if adiposity is the main culprit.)   That would seem to be an empirical question.

 

Turning excess calories into muscle may be much preferable to turning them into fat,  but it may still not be ideal.

[mccoy]

 

since calories are not always turned to fat.

 

That's the point.   How do we know that it is excess fat entirely (one particular result of excess calories),  and not excess calories per se (as well),  that is the causal link between BMI and mortality?

 

We should ask that to the BMI researchers. They would maybe answer that usually excess calories are turned into fat so the two things are positively correlated, calories being the cause and adiposity being the effect.

 

 

My point is that I'm not sure  you can draw the "not applicable" conclusion strictly by logic.   There's no purely logical reason that excess calories in and of themselves could not have at least some negative impact on longevity (even if adiposity is the main culprit.)   That would seem to be an empirical question.

 

Turning excess calories into muscle may be much preferable to turning them into fat,  but it may still not be ideal.

 

That's a CR issue. Again, it seems that we have no data on humans. On lab rats, according to the literature cited by Michael Rae, exercise does not increase longevity. In larger mammals, like monkeys, we don't even know for sure that CR has beneficial effects on lifespan. On humans, still worse, we don't have long term controlled trials of CR versus lifespan, nor there are data on the multiple correlation among CR, lifespan and exercise.

[mccoy]

Yet another article which suggests that adiposity is viewed as the cause of higher mortality in the higher BMI regions and that an high BMI in athletes may not be a good predictor of mortlity.

 

DEXA or BMI: Clinical Considerations for Evaluating Obesity in Collegiate Division I-A American Football Athletes

[mccoy]

This is a good plot on the correlation between total adiposity and BMI. Men are blue, women are red.

The correlation is pretty good, although there is some variability. a 22.5 BMI may mean an adiposity ranging from 10% to 18%.

 

 

Edit: the above data are referred to a korean population. Korean males tend to be more adipose than westerners 

[mccoy]

Yet another study on BMI, interesting though. Here bodyfat and BMI are used as distinct variables in the model, and BMI becomes a proxy for lean body mass.

When BMI is used as a proxy for lean body mass the hazard ratio decreases with increased BMI.

 

Relationship Among Body Fat Percentage, Body Mass Index, and All-Cause Mortality

 

 

Bottom line: is the overall mortality governed by lean body mass or adiposity? So far, we can observe these effects:

 

1. More adiposity means more mortality (except very low adiposity suggestive of malnutrition)
2. More lean mass means less mortality (except the freakishly huge, suggestive of drug abuse)

So, if we build a two-variables function, mortality as a function of adiposity and lean body mass, we should be able to underline the minimum, or a significant minimum of the function, where an optimum condition of bodyfat and lean bodymass is visible. I don't know if anything has been done, I couldn't find any function-of-2-variables plots.

 

In the above article, and in similar articles, in not young populations more bodyfat seems to improve the survival odds, even as more lean body mass. This apparent contradiction with the previous analyses is called 'the obesity paradox'.

30% bodyfat and BMI 26 kgm-2 seems to be the optimum. 

 

Yet no specific data on athletes

 

Values below only for the men subset

[Todd Allen]

With respect to 30% body fat being optimal for mortality I wonder if there are any confounders involved such as some percent of people of lower body fat %s also having poor nutrition and/or health issues that contribute to leanness, for example many people with cancer become quite lean without getting healthy.  If we studied what percent of body fat correlated with optimal mortality in a healthy population with little obesity would we come up with a different result?

 

For men, 30% bodyfat is typically considered obese.  If 30% is truly optimal for human mortality across all populations it seems like the obesity threshhold ought to be higher.

[AlPater]

C'mon, cannot you see that the lows of the curves are about 33 for the BMI and less than 15% for the fat mass percent?

[mccoy]

C'mon, cannot you see that the lows of the curves are about 33 for the BMI and less than 15% for the fat mass percent?

 

Right, sorry for the confusion and thanks for pointing out!

Lower bodyfat means less mortality is the known research. Barring extreme emaciation.

Whereas the obesity paradox would be explained by the BMI being a proxy for lean mass rather than adiposity.

Still the sample would need to be examined more thoroughly, since it appears that it's made of 40 and more aged people, with some backbone and hip problems. Ostensibly no weightlifters and bodybuilders in their prime.

 

 

Study Design We performed a population-based cohort study of all eligible residents of Manitoba, Canada, who were aged 40 years or older and who had initial dual-energy x-ray absorptiometry (DXA) of the spine and hip for bone mineral density (BMD) testing between 1999 and 2013.