Numerical models for determining Max TDEE deficits

Mr_Knight

I've been trying to formalize the relationships between all the various energy stores in the body (glycogen, adipose fat, intramuscular triglycerides), energy sources (ingested food), and calorie burns (BMR, non-exercise, exercise). So I have this spreadsheet laid out where I map the rates of all these processes on an hour by hour basis. IE, at 0300h, the body is sleeping and burning at the BMR rate. At 0900h, it is burning BMR + non-exercise + resistance training, and digesting a pre-workout meal of 20% of the daily intake of carbs/protein/fat.

From the literature, I pulled a number of rates that are used in all this:
- Fat stores metabolize at 30 calories/day/pound of fat
- Intramuscular triglycerides metabolize at 80% of fat store metabolism
- Glycogen stores are tapped when instantaneous burn is greater than fat stores and ingestion can provide
- Glycogen stores are replenished when the opposite is true
- Carbs/Protein/Fat are metabolized at 60g/8g/5g per hour
- Resistance training co-opts 75% of protein for rebuilding if there is enough energy from other sources

So now I get to play with the numbers. I can create a body that weighs X pounds with Y% body fat, with whatever exercise burn pattern I like over a 24 hour period, and find the lower limit on sustainable TDEE deficit by seeing when glycogen stores are no longer able to replenish. Obviously the numbers are totally dependent on the quality of assumptions around metabolic rates.

This is a sampling of what I see - with a *daily* routine of one hour resistance training (300 calories) in the morning and one hour of intense cardio (1000 calories) in the afternoon...

A person with 30% body fat can support a TDEE deficit of 50%
A person with 20% body fat can support a TDEE deficit of 25%
A person with 15% body fat can support a TDEE deficit of 10%
A person with 10% body fat can't support a TDEE deficit at all

By "support" I mean the body starts with glycogen stores that do not deplete over the 24H cycle, allowing the exact same activity to be performed the next day. Taking days off will obviously increase the size of the supportable deficit. This does not take into account nutrients at all - that's just too complex for me to model at this point.

There is a crapload of interesting relationships that pop up - IE, resistance training reduces size of the max possible deficit at any given body fat %age (that's a Good Thing!) and if you don't fuel with carbs while lifting, there won't be any protein available for muscle building because fat stores can't provide energy fast enough.

Anyway, it's entirely possible I've completely screwed this up. The results look kinda reasonable, so far, but I'd be very curious is anybody else has gone through an exercise like this, or knows of a paper/article that ties all these rates and factors together into a numerical model.

yarwell

I haven't seen any "during the day" modelling, http://www2.niddk.nih.gov/NIDDKLabs/IntramuralFaculty/HallKevin.htm does longer term models and does have body fat and macro considerations in there, so that may go somewhere.

Does the model take account of the different substrate utilisation at different heart rates, and the effect of diet on the mix ? I've observed in the literature that high carbohydrate eaters use a lot more carbs at rest than low carb dieters do.

If you look at an African marathon runner during a marathon does it hold up OK ?

ETA: 1000 calories/hour of cardio is 200 litres/h of O2 or 3333 ml/min. A 220 lb / 100 kg person would have an aerobic level of 33.3 ml/min/kg at that, which is above my VO2max and that of quite a few other people.

Mr_Knight

There are some nice looking publications at that link - thank you!

I started building this model (which is still a work in progress) mostly to understand if the standard MFP story - that macros and meal timing/composition don't matter, only calories do - was true. At this point, I believe it is only true under certain conditions - relatively light exercise loads and "mixed" meals (ie, plenty of carbs + protein in each meal). And I'm not convinced right now that it holds for anything other strict weight loss - if body recomposition is important, it appears macros and timing do appear to matter.

Next step is to move it from a spreadsheet model to actual software. That will make it easier to account for issues like the one you mentioned re: V02max (good catch, thanks for that!)

I have some solid reading to do - thanks again for the link!