What is a reasonable ad libitum calorie allowance for humans? I MAY have a (possible) answer.

[GenGenimney]

I've been gone because I forgot my password and was too lazy to reset, and I'm still quite skeptical (perhaps MORE skeptical, honestly) of the benefits of extreme CR in humans.  (Sorry/not sorry.)  Buuutttt since my target weight is a lean 17-19 BMI, and since I want to keep doing ON regardless, I guess I'm a non-CRONie CRONie or something.

 

I've been puzzling over "What IS CR?" off and on for months, and then suddenly I remembered an article I read a few years ago that might have an answer:  "Constrained Total Energy Expenditure and Metabolic Adaptation to Physical Activity in Adult Humans."  http://www.cell.com/current-biology/fulltext/S0960-9822(15)01577-8

 

For some reason, my screen capture plugin doesn't work on the site, but anyway, researchers found that "calories out"/TDEE doesn't vary a whole lot among different populations, even with very different lifestyles.  Their basic model came up with a figure of 2309+/-38.4 calories, when controlled for a number of things.

 

I'm not sure how to use this, fully, as many of the things that are controlled for (like fat mass/fat free mass) are obviously altered by intake.  I think we can probably say that around a BMI of 25 is probably an honest ab libitum number, without food shortage and with normal levels of activity.  (Looking at worldwide average BMIs:  http://visual.ly/weight-world) Then you could plug in that weight into the typical age- and sex-specific body fat percentage to get the rest of the info you need to calculate a baseline TDEE:  http://halls.md/body-fat-percentage-formula/

 

That would give a woman my height (5'6") a baseline of 2007 cal/day, with no physical activity.  The minutes per day of physical activity threshold is 200, so plugging in 200 (assuming this give you the body's happiest level of activity), I end up with 2288 calories as the ad libitum value with a steady weight (though I should probably add a tiny bit to that for "better" foods being less efficiently processed...).  200 minutes per day of light activity is another 280 calories for my size, which is above light but under moderate exercise. 

 

A 10% CR would be 2050 calories TDEE, which would be, interestingly enough, a BMI of 18 with heavy exercise or 21 with moderate exercise or 27 with light exercise.  A 20% CR would be 1830 calories, or a BMI of 13 (aka dead) with heavy exercise, about 17 with moderate exercise, and 22.5 with light exercise.  A 30% CR would be 1600 calories, or a BMI of 11.5 (aka dead) moderately active, 16.5 lightly active,  and 22.5 sedentary.  (Add on a little for inefficiencies of digestion.)

 

 

We know that caloric restriction that extends life does NOT reduce daily activity in mice.  It seems reasonable to assume that the maximum human caloric restriction would be less than that requires to maintain somewhere between a light and moderate activity level, possibly a fully moderate activity level.  This in turn means that no more than a 30% CR would be safe for humans, and that the baseline TDEEs are probably higher than what we've previously assumed.  

 

A 10-25% CR from the "free-living" ad libitum values for typical healthy human populations with light to moderate activity would be a level that most people wouldn't feel the need to conserve energy, which would be contrary to the animals who have benefited from CR in the past.  I think we DO see that in the mortality curves of healthy people with low-normal/high-low BMIs, and I think we hit a TDEE wall above a CR of about 25%.  People tend to maintain their weights and intakes less scientifically than researchers do for mice, so the curve might be a bit more generous if you are stricter about it, but that's all.

 

These figures do bring up the suggestion that CR really does happen fairly frequently "in the wild" among humans, which would bolster my contention that there probably is pretty limited benefit, a benefit we already see not too infrequently today, of no more than a 2-10% lifespan increase.  In humans, this would be dwarfed by other factors (like the ON side of things!!!).  We don't see that people who sit on their butts and stay at a BMI of 17 live a lot longer than people who workout and have a BMI of 20, for instance, much less that people with a BMI of 18 who work out die younger than people with a BMI of 18 who don't.  If people were like mice in this way, they should!  Even if we assume a baseline BMI is 22 (which we don't really have evidence for), we still should be able to see some level of trends with that.

 

Anyhow, this is a bit babbly, but anyway, a few things to chew on.

[Michael R]

It is operationally impossible to measure "%CR" in individual, free-living humans consuming self-selected diets and with self-selected activity levels.

 

However, it is simply not plausible that any but a very small percentage of the general population are on anything resembling CR. By definition, CR involves feeding an organism less than it ostensibly "needs" to meet its normal metabolic requirements. In properly-done CR studies, researchers take a colony of (usually) genetically homogeneous animals living under identical conditions, with identical opportunity for exercise (and, usually, genetic disposition to take advantage of those opportunities) and eating identical diets, and first determine how many Calories to which they default. This is the condition of nearly everyone in the general population in industrialized countries, and large numbers of people in developing ones.

 

The "ad libitum" controls then get fed 10-15% less than this default amount in order to avoid the confounding effects of obesity. Only a small percentage of the human population is even willing to discipline itself to this small degree of restriction.

 

The CR group is then restricted by 30-40% below that, often starting at weaning, and are kept that way day in and day out for most or all of their lives. Their entire metabolic apparatus undergoes radical reorientation to adapt. CR females cease estrus; CR males have extremely low sperm counts. No one is "spontaneously" doing anything like this; really, no one is even doing what the "ad libitum" rodents do as their default. It all requires a level of self- or environmentally-imposed restriction of food intake.

[sirtuin]

A 10% CR would be 2050 calories TDEE, which would be, interestingly enough, a BMI of 18 with heavy exercise or 21 with moderate exercise or 27 with light exercise.  A 20% CR would be 1830 calories, or a BMI of 13 (aka dead) with heavy exercise, about 17 with moderate exercise, and 22.5 with light exercise.  A 30% CR would be 1600 calories, or a BMI of 11.5 (aka dead) moderately active, 16.5 lightly active,  and 22.5 sedentary.  (Add on a little for inefficiencies of digestion.)

I've been playing with CRONometer for a year or so, tracking most of my daily food intake usually with a food scale (CJ4000).  My exercise is usually <30 minutes in a day (olympic lifting / calisthenics / occasional light jogging), sometimes this exercise is just 5-10m or so (HIIT), and I take at least 2 days off from exercising throughout the week where I'm otherwise working at a desk for most of the day with an occasional walk around the block (~5,000-15,000 steps per day.)  My Nutrition Report for Jan 1 through March 1 puts me at an average of 2358 kcal/d (upwards of 2700kcal some days),  where I'm 139lb at 5'10" with a BMI < 20.  In the past, I was tracking closer to 2,000-2,200 where I seem to be eating more food lately or weighing things heavier.

 

I'm guessing that I'm greatly overestimating caloric intake (although I stuff myself at most meals and often use a food scale) ?  By volume, I'm easily eating twice the amount of food as my guests.  Perhaps I'm greatly underestimating exercise and NEAT?  Or there's some averaging effect of large gaps spent fasting with a low caloric intake and blips of higher caloric intakes around higher amounts of activity.  It seems like I'm somewhere between -30%CR by caloric intake and +30% by low-activity BMI.   Taking my blood pressure today, I was 94/54 which seems fairly consistent with caloric restriction (or maybe I just need to substantially up my sodium intake.)

 

This is an interesting list of countries by caloric intake:

https://en.wikipedia.org/wiki/List_of_countries_by_food_energy_intake

 

Apparently a 1,700kcal diet is 2,000kcal less than a typical american diet.

 

Quantifying the % level of CR seems fairly difficult in practice.

[Michael R]

Quantifying the % level of CR seems fairly difficult in practice.

I say again: it is operationally impossible to measure "%CR" in individual, free-living humans consuming self-selected diets and with self-selected activity levels.