"Starvation mode", exercise calories, dillema?

What do you mean by underfeeding? Are you saying that people who chronically eat below their TDEE experience adverse health effects? Or when you say underfeeding are you speaking of below BMR?

Also, I really don't understand what you're saying in the last paragraph I quoted. If I go to webMD and use their metabolism calculator to find my TDEE, then why do I need to multiply by 25%?

to answer your first question. Underfeeding is any time you eat below TDEE yes, but as I stated, in order to begin and continue in the process of starvation mode, you must underfeed enough to not be able to maintain the deficit. think of it like this:

if Calories consumed + energy from storage (fat, protein...etc) =TDEE
then
You can maintain the deficit and lose fat.

BUT
If Calories consumed + energy from storage is LESS than TDEE then eventually, your body will continue to use glycogen at a greater rate then it can be created, eventually the body will require a means to balance out, this means adusting the energy burning portions of the body (muscles organs, autonomic functions, heat, immune system...etc)
This is a long slow process, but eventually it can become dangerous.

AND
The more fat you have, the larger the amount of energy the body can pull to make the equation above equal out.
But the body can only use so much fat, because it can't pull fat from unexposed areas (think of a melting ice cube, you can't melt the middle until the top is melted). So there's a finite amount of energy that the body can pull from fat at any one point in time.

as to your second question. I probably should have been clearer on that. WebMD is a TDEE calculator, so no need to multiply by your activity level. If you're using a BMR or RMR calculator then you would, but not if it already asks for your activity level.

Abstract
A limit on the maximum energy transfer rate from the human fat store in hypophagia is deduced from experimental data of underfed subjects maintaining moderate activity levels and is found to have a value of (290+/-25) kJ/kgd. A dietary restriction which exceeds the limited capability of the fat store to compensate for the energy deficiency results in an immediate decrease in the fat free mass (FFM). In cases of a less severe dietary deficiency, the FFM will not be depleted. The transition between these two dietary regions is developed and a criterion to distinguish the regions is defined. An exact mathematical solution for the decrease of the FFM is derived for the case where the fat mass (FM) is in its limited energy transfer mode. The solution shows a steady-state term which is in agreement with conventional ideas, a term indicating a slow decrease of much of the FFM moderated by the limited energy transferred from the fat store, and a final term showing an unprotected rapid decrease of the remaining part of the FFM. The average resting metabolic rate of subjects undergoing hypophagia is shown to decrease linearly as a function of the FFM with a slope of (249+/-25) kJ/kgd. This value disagrees with the results of other observers who have measured metabolic rates of diverse groups. The disagreement is explained in terms of individual metabolic properties as opposed to those of the larger population.

What do you mean by underfeeding? Are you saying that people who chronically eat below their TDEE experience adverse health effects? Or when you say underfeeding are you speaking of below BMR?

Also, I really don't understand what you're saying in the last paragraph I quoted. If I go to webMD and use their metabolism calculator to find my TDEE, then why do I need to multiply by 25%?

to answer your first question. Underfeeding is any time you eat below TDEE yes, but as I stated, in order to begin and continue in the process of starvation mode, you must underfeed enough to not be able to maintain the deficit. think of it like this:

if Calories consumed + energy from storage (fat, protein...etc) =TDEE
then
You can maintain the deficit and lose fat.

BUT
If Calories consumed + energy from storage is LESS than TDEE then eventually, your body will continue to use glycogen at a greater rate then it can be created, eventually the body will require a means to balance out, this means adusting the energy burning portions of the body (muscles organs, autonomic functions, heat, immune system...etc)
This is a long slow process, but eventually it can become dangerous.

AND
The more fat you have, the larger the amount of energy the body can pull to make the equation above equal out.
But the body can only use so much fat, because it can't pull fat from unexposed areas (think of a melting ice cube, you can't melt the middle until the top is melted). So there's a finite amount of energy that the body can pull from fat at any one point in time.

as to your second question. I probably should have been clearer on that. WebMD is a TDEE calculator, so no need to multiply by your activity level. If you're using a BMR or RMR calculator then you would, but not if it already asks for your activity level.

Just to add a little piece of data that I found very useful for calculating calorie deficits:
http://www.ncbi.nlm.nih.gov/pubmed/15615615

Abstract
A limit on the maximum energy transfer rate from the human fat store in hypophagia is deduced from experimental data of underfed subjects maintaining moderate activity levels and is found to have a value of (290+/-25) kJ/kgd. A dietary restriction which exceeds the limited capability of the fat store to compensate for the energy deficiency results in an immediate decrease in the fat free mass (FFM). In cases of a less severe dietary deficiency, the FFM will not be depleted. The transition between these two dietary regions is developed and a criterion to distinguish the regions is defined. An exact mathematical solution for the decrease of the FFM is derived for the case where the fat mass (FM) is in its limited energy transfer mode. The solution shows a steady-state term which is in agreement with conventional ideas, a term indicating a slow decrease of much of the FFM moderated by the limited energy transferred from the fat store, and a final term showing an unprotected rapid decrease of the remaining part of the FFM. The average resting metabolic rate of subjects undergoing hypophagia is shown to decrease linearly as a function of the FFM with a slope of (249+/-25) kJ/kgd. This value disagrees with the results of other observers who have measured metabolic rates of diverse groups. The disagreement is explained in terms of individual metabolic properties as opposed to those of the larger population.

Basically, the maximum amount of energy that can be extracted from fat stores per day is ~290KJ per kg of body fat, or 31 calories / pound of fat. Anything over that deficit will have to come from other reserves and contributes to underfeeding.

ooh, that's a great post. Thanks kaervaak! I've been looking for something like this for a while.