Travis, thank you posing such an interesting question. I'm not a fellow, but, here are a few thoughts: :)

The ideal body fat for optimal health depends, at least, on one's sex, age, genetic make-up, health history/parameters, type of physique (for lack of a better description), professional demands, and one's goals in life.

I have read studies about lean body mass and weight in older people, and some predictions for longevity, but those studies were all based on the SAD and the controls were not ones based on a Paleo approach to eating. The blog articles I have seen, all quote these studies based on the SAD, which makes any conclusions questionable.

I don't count on many future, sound, relevant, clinical trials based on a Paleo diet, because there isn't much money for the multi-national, pharmaceutical conglomerates if studies based on real foods prove that people live longer and healthier lives on real food, and, therefore, use very few medicines. The conclusions of studies based on real food could expose the misdeeds and ignorance of the politicians who have used propaganda to push agricultural products, by-products and waste. The emperor doesn't wish anyone to know he wears no clothes.

Dr. Jan Kwasniewski, author of the Optimal Diet, uses one's height in centimeters minus 100, plus or minus ten percent, as a gauge for ideal weight for health and longevity.

Example: If a person is 190 cm tall minus 100 = 90 Kg, plus or minus ten percent.

The book states the same formula for women and men. (I don't know if people in Poland need to weigh more.)

Dr. Kurt Harris and Peter Dobromylskyj, each, have written some about Dr. Kwasniewski's views.

Here is the link to Dr. Kwasniewski's site, translated into English by Google translator:

http://translate.google.com/translate?hl=en&ie=UTF-8&sl=pl&tl=en&u=http://dr-kwasniewski.pl/%3Fid%3D2%26news%3D80&prev=_t&rurl=translate.google.com

and a site in English, out of Australia:

http://homodiet.netfirms.com/index.html

Peter Dobromylskyj, who writes the blog, Hyperlipid, has written about the question of weight, with his usual honesty and astuteness.

At the end of this blog article:

http://high-fat-nutrition.blogspot.com/2008/05/weight-loss-when-its-hard.html

Also the final thought must be: What is the healthiest weight, personal preferences aside? I don't think we know.

As is often the case, there are many gems of his in the comments, as well as in his blog articles.

If I should find any abstracts or full texts on ideal body fat for longevity which I think worth noting, I will post them here.

The question of ideal amount of lean body mass and fat for one's own health and lifespan are very much a present question.

I look forward to reading others' posts.

I don't know about optimal body fat for health and longevity, but I know my goal was to get under 25% and now that I've been eating Paleo for a few months I'm hovering around 20-22%. It is absolutely perfect FOR ME. I like the way my body looks here. I like my strength. I am eating more than I have in 6 years, but less carbs and more protein. It's perfection for me.

I get tempted sometimes to push it lower, but I actually don't want to lose my breasts and that's what happens when I get around the 20% mark. I'll take the extra junk in the trunk to keep the rest of the me where I want it.

I agree with coach Charles Poliquin, an ideal bf for a male (in terms of balancing performance and longevity) is between 6 and 10%. How do you know if you're under 10? You can see your lower abs.

Interestingly, Martin Berkhan uses the same formula as Dr. Jan Kwasniewski for ideal weight, ht in cm - 100 = ideal weight in kg.

His standards are a bit different, however. He argues this is your max muscular bodyweight for a "contest-ready" bodybuilder. Meaning around 5-6% bf and slightly dehydrated. So their walk-around weight would be ht minus 95-97= max bodyweight.

This is an interesting question, but there is one aspect to consider. Hunter-gatherers were just that. Even if they were skilled at acquiring food and tribal knowledge was extensive, surely there were times when the hunt was bad, the fish didn't run or roots & berries were scarce, etc. In these situations it would have been a disaster to be sitting at 6-8% body fat; bad hunting for 2 weeks and you'd be gone. Also, the image of beauty itself probably would have included some fat as sign of plenty and wealth. So lean but not ripped/shredded probably the norm.

Our society is obviously a totally different matter. Though some people on SAD may be starving for nutrients, there is little real starvation due to scarcity (ie, food just not around and not enough calories to sustain life). Food is pretty much everywhere and if you really needed some calories to survive you can get them. Most of us considering this question may skip a meal or two sometimes or even frequently, but if we wanted to eat we can eat. So it is much less threatening to be at 8% body fat in this situation.

HGs I see pictures of don't sit at 10-12%...The active healthy (male) ones all have abs.

I think its a matter of set point, once you get down to 8% it's prettyeasy to hold there... It's working down your setpoint that's the fight.

Edit: to be clear, I think the # is in the 8-10% range for active individuals.

I don't think you hit danger are till 6% or less.

I feel the need to add further opinion. I dont think Bodyfat is at all important for Health and Longevity, other than too much visceral fat will harm both. subcutaneous is likely to be fine...

Muscle on the other hand is strongly correlative to longevity.

In cold climates having a little extra bodyfat is healthy i think. We had the coldest and longest winter for ages last year and i felt cold as hell. I have been leaner in the past when i was doing 400kms a week with road cycling and always freeezing during winters. Ofcourse it is great to be lean in very warm and humid climates. This is always very personal thing, and best way to know is to get to know your body! For some 8-10% is great, for others maybe 15% might be healthier?

I think the idea that the best % BF for mortality is sub 10% or even sub 20% is not supported by observation. See this: http://intranet.santa.lt/thesaurus/no_crawl/BENDRI/Impact%20of%20obesity%20on%20total%20and%20cardiovascular%20mortality%E2%80%94fat%20or%20fiction.pdf

From figure 1 of the reference, for both all cause mortality and cardiac mortality the lowest relative risk is achieved with BMI's between 25-30. Now before you go off about how crappy BMI is as a measurement, hear me out.

Figure 2 of the reference shows the statstical variation in body fat% among men and women who have a BMI of 25, the lower end of the lowest mortality risk group. Fig 2 clearly shows that there are very few individuals with a BMI of 25 that have BF% below 15%. The vast majority of men with BMIs of 25 have BF% between 18% and 32%.

If you believe these statistics have been accurately gathered and presented, then you might conlcude that the lowest relative risk for mortality is in men with around 18-32% body fat and women with around 28-40%.

I don't consider this to be definitive in the sense that we want to be in those BF% ranges. But I do consider this to argue strongly against the idea that men should be 8-12% body fat for best longevity.

The reference does conclude that it might be far more accurate to take into account body composition as well as body fat in determining mortality.

Here's an anecdotal longevity perspective based on interviews of 30 US centenarians described in the book "Extraordinary Centenarians in America: Their Secrets to Living a Long Vibrant Life".

None of them had exercise routines, but they were all active in a more conventional way, as compared to HG. They ate home cooked meals, were not "health conscious" per say, but real food based.

I was surprised to find that most had siblings who died <70 from disease, implying genetics is less of a factor than I would normally think.

They were not obese, but were also not going out of their way to reduce body fat, making me tend to believe they didn't have ab-revealing BF%.

on my guesstimate, minimally appropriate level of bf would be one at which you are able to pull yourself up hanging from a precipice, and climb on it; the ideal would be one at which you're able to do the same but holding an additional load the same as your own weight

You guys claiming 6 to 8 percent crack me up. You're all full of it and aren't honest enough to admit it.

whether 8% or 15% - doesn't matter for health and longevity, as long as it doesn't cause (or is caused by) chronic inflammation and derangement of metabolism or appetite control. i'd say it's perfectly possible to be fit and 100% healthy at 15%, and even live as long (or even longer) than the next hobby bodybuilder at 8%. higher BF is not per se detrimental to health - but carrying it mainly as visceral fat and being sedentary probably is. so, fat deposition/distribution, overall health and fitness is at least as important as total BF%.

Show me a single instance of someone with a lot of muscle living a long life.