Concerns with Ambiguous TDEE Calculation (Link Inside)

Ploogy

Finally, I found someone else who shares my concern with these so called "activity factors" and how amorphous they are. Hopefully this helps out some others in how they go about calculating TDEE (and the resulting caloric defict to follow).

http://calorieline.com/tools/tdee#clinebmr

An excerpt:

Unlike most TDEE calculators online, this is the only use we make of so-called 'activity factors' (see below). For the TDEEs of more active persons, we use the TDEE of a sedentary person as a baseline, and then add the calories burned by the physical activity in each scenario using this equation:
Calorie Burned = Weight (kilograms) * Time (minutes) * MET
The MET values are taken from Compendium of Physical Activities: an update of activity codes and MET intensities

A premise of Calorie Line's weight, exercise, and calorie trackers is that the best way to figure out your TDEE is to measure how many calories you eat (as best you can), how much exercise you get, and what your weight is on a regular basis. Then, you can simply see how caloric intake and exercise effect your weight by looking at your graphs. But if you are just starting out at tracking your calories, then using our TDEE estimator can provide a guideline for coming up with goals for caloric intake and exercise.

How Everyone Else Estimates TDEE
Note that most TDEE calculators online make their estimation by multiplying your BMR (the calories you burn at rest) by an activity factor [FOR REFERENCE -- WE DO NOT USE THESE!]:

Sedentary = BMR X 1.2 (little or no exercise, desk job)
Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk)
Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)
Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)
Extr. active = BMR X 1.9 (hard daily exercise/sports & physical job or
2X day training, i.e. marathon, contest etc.)

Just about every TDEE calculator on the web uses the above classifications, called 'activity multipliers' or 'activity factors,' and multiplies them by estimated REE or BMR to estimate TDEE. These factors have found their way into books, online calculators, university lecture notes, and on and on. (See them for yourself)

So why are we the only ones that won't use them? Well, the first clue is that just about nobody bothers to say where these activity factors come from. It turns out they come from 'Energy and protein requirements: Report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series No. 724', a report released in 1985 by the world health organization (WHO). Even the WHO's own 2001 expert group doesn't sound too keen on these classifications anymore:

The report from the 1985 FAO/WHO/UNU Expert Consultation used a set of equations derived mostly from studies in western Europe and North America. Almost one half of the data used to generate the equations for adults were from studies done in the late 1930’s and early 1940’s on Italian men with relatively high BMR values, and questions have been raised about the universal applicability of those equations.
- INTERIM REPORT: FAO/WHO/UNU Expert Consultation Report on Human Energy Requirements (see section 5.2) (PDF LINK)

That is why we don't use the same TDEE formula as everyone else. We believe that what passed for 'lightly active' for an Italian man during the Great Depression and WWII may not pass for 'lightly active' today.

Our own skepticism towards the 'activity factors' originated from seeing discrepancies between the TDEE numbers that come from using the activity factors vs. the numbers we would expect from using the more recent MET values from the 'Compendium of Physical Activities: an update of activity codes and MET intensities' (see references below). For example, the activity multiplier technique predicts that a 43 year old, 6 foot, 200 pound male who is 'lightly active' (does sports 1-3 times per week) needs to average about 2535 calories daily to maintain his weight after multiplying his estimated REE of 1843 by 1.375. If we multiply the REE times 1.2, we get 2211, the number of calories that a very sedentary, but not bed-ridden 200 pound man burns per day. That same man then has to burn another 323 calories per day on average through physical activity for an overall TDEE of 2535. To put that amount into perspective, that same 200 pound man would have to jog (assume MET of 7 from the Compendium) for 70 minutes 3 times per week to burn that many of calories. Sure, it's doable, but it doesn't sound much like 'lightly active, sports 1-3 days/week' either, it sounds more like 'kind of sporty, physical activity 2-4 days/week,' which is not currently a category.