muscle loss and calorie deficits

As I understand it, there is also a genetic component to calorie partitioning or where the energy deficit comes from (or alternatively where the surplus goes when in a surplus situation). I was just reading on Body Recomposition (is that Lyle Macdonald?) about this. He calls it P-ratio. Some people are genetically predisposed to crappy partitioning where they put on, say 50%fat and 50%muscle in a surplus and then lose 1/3 muscle and 2/3 fat in a deficit. Any deficit.

^The primary predictor of P ratio is starting bf% (Lyle McDonald, Initial Body Fat and Body Composition Changes). From my understanding, a leaner individual will lose more LBM during a deficit, and gain more LBM on a bulk. Subsequently, the fatter you are, the more fat you will lose in a cut, and the more fat you will gain in a bulk. However, there is also a monkey-wrench - dieted down lean vs naturally lean. Hormonal and metabolic adaptations will also play a role in LBM lost or gained in naturally lean vs dieted down individuals.

Basically, the human body is much smarter than we are. Unfortunately, we can't "manually" partition our calories and decide where we experience weight gain or loss.

It matters because fat can only be "burned" (converted and used) at a rate of roughly 31.4 calories per pound per day, so even if you are doing other things right if the deficit can't be serviced fast enough using fat then the body has to use other things.

I'm oversimplifying here, I know... but I need something more tangible to help me understand...

Say I have 30lbs of fat. 30lbs * 31.4 calories per day = 942 calories. That means that my fat mass can account (make up for?) a maximum deficit of 942 calories.

Again, oversimplified I'm sure, but for the sake of conversation/understanding...

Not over simplified; correct AFAIK. I have seen an article that number comes from. Someone linked to it in another post and I think it was on NIH. As hotly as some things get debated, that one seems pretty widely accepted. That does not mean that the body will provide the 942 calories though. It just means it can and based on other studies and experience my opinion is that if you were to have a 942 calories deficit, it would more likely get less than 800 of that from fat. I am not sure why, but there almost always seems to be LBM loss even when people are doing what seems like the right things. Based on BF% before and after my loss of 55 pounds, I think I lost over 75% fat. I am good with that. I would rather be where I am now.

Nice timing on the thread. I've been thinking over the past few days about how to determine absolute rock-bottom safe limit on calorie intake.

To scope this down I'm going to assume my standard dieter, a 250 pound male with 35% body fat.

Protein -> 1g/LBM pound -> 160g/day -> 640 calories/day
Fat -> 0.35 g/LBM pound -> 56g/day -> 511 calories/day
Carbs -> 0.75 * Protein -> 120g/day -> 480 calories/day

Totals to 1631 calories. A person of this size with a decent activity level should be burning at least 3200 calories/day. So a daily deficit of 1600 calories, which is certainly within the limits of what the fat stores can provide (2000 calorie/day, conservatively).

The implications of this, if close to correct, are interesting. Namely, even someone carrying an extra 50 pounds of fat is going to have issues retaining lean body mass if they want to lose at a rate of 2 pounds/week. Really, the only way to get there would be to jack up the carb intake so you can jack up the cardio so you can create a same-percentage deficit off of a bigger TDEE. But then we're no longer talking about "rock bottom calorie intake".

Dug up an article that refers to the source for the 31.4 calculation and has some other interesting details:

http://baye.com/calculating-the-daily-calorie-deficit-for-maximum-fat-loss/

One thing it has is an example very similar to what was mentioned earlier, though the author rounds to 30 cals:

For example, a 200 pound man at 15% body fat would have 30 pounds of fat, enough to provide about 940 calories of energy over the course of a day. Assuming he reduced his calories intake to 940 below maintenance for a day, by the end of the day he would have lost about a quarter pound of fat, which would require the deficit to be reduced by about eight calories the next day.

Someone else said they thought 2000 a day from fat was conservative. For an obese person, it may be. It is odd that the author used 15% BF as an example.

The actual study is:
Alpert SS. A limit on the energy transfer rate from the human fat store in hypophagia. J Theor Biol. 2005 Mar 7;233(1):1-13.

Dug up an article that refers to the source for the 31.4 calculation and has some other interesting details:

http://baye.com/calculating-the-daily-calorie-deficit-for-maximum-fat-loss/

The actual study is:
Alpert SS. A limit on the energy transfer rate from the human fat store in hypophagia. J Theor Biol. 2005 Mar 7;233(1):1-13.

Thanks mate

I think this is a key point.

Keep in mind the specific foods and macronutrient ratios consumed by the subjects were far from optimal for fat loss, and that “moderate activity levels” is not the same as regular, high intensity strength training. The maximum rate is most likely higher for someone eating adequate protein and not overdoing carbohydrate intake and strength training would also contributes to maintenance of lean body mass when calorie intake is below maintenance level.

For optimal LBM retention, increased protein intake and resistance training would be done unlike in the Minnesota starvation experiment. How much difference that makes???

True. It's not like our bodies work in exact 24hr cycles like we use for recording. It's also unlikely that any appreciable amount of LBM gains could even happen in 24hrs of being in a surplus.

Someone else said they thought 2000 a day from fat was conservative. For an obese person, it may be. It is odd that the author used 15% BF as an example.

I'm the "2000 is conservative" poster. It was specifically for the case of a 250 pound male with 35% body fat (Ie, obese, or nearly so).

Taking it a step further, let's add in some running for cardio. 60 minutes, 6 miles, 10 min/mile.

Net calorie burn per mile is 0.63 * bodyweight -> 157 cal/mile -> 945 calories/hour running. In that same hour, fat stores provide around 1 calorie/pound of fat store, or right around 100 calories during that hour of running. This leaves a deficit of over 800 calories that cannot be filled from fat stores, so it has to come from a combination of glycogen stores and digested calories. So you can see right away that the protein guideline falls apart if you do cardio, because you are going to be burning protein for fuel before it gets a chance to "build muscle".

So you need carbs if you're going to do cardio and want to save the protein for LBM maintenance - unless you're go to something like a 2g/LBM guideline, but then we have to consider the limits on how fast protein can actually be metabolized for fuel. Whatever that rate is, it's slower than it is for turning carbs into fuel. Much slower. My understanding is even the high performance gels, taken with perfect timing, do not prevent glycogen depletion in endurance racers, which means relying on protein metabolism will inevitably fry your glycogen stores.

Whew!

You can actually lay this stuff out in a spreadsheet, showing where calories enter the body, where they enter "the system", where they come out for specific exercise, etc. It's a neat exercise, pretty eye opening, as it forces realization that the body does things a little bit at a time, all the time.

From my personal experience, readings and discussions, if you train well for a half marathon you will not suffer glycogen depletion even if you take nothing during the run. I have not run a full marathon, but my understanding is that nearly everyone but the elite distance runners will suffer glycogen depletion during a marathon even if they take energy beans/gels during the run. The elite runners may dodge it by a combination of large reserves and efficiency.