Eating back for Exercise vs Activity

I'm curious too. I've been using the MFP method, and as long as I'm honest with myself in my logging, it's been fairly accurate.

I think you made one mistake in your assumption.
For the teacher person you assumed for fat loosing she has to have 1000 cal deficit to lose 1lb/wk whereas this is for double that.With 1200 net cal you calculated TDEE - almost 50%
The teachers net target in fact would be 2200-500 so 1700 and not 1200. This is the error you`ve made according to me.
The desk job person has a basis with 500 cal deficit at 1200.
So the teacher person in fact is going to lose twice as fast with the calories you wrote down.

I'm not exactly sure where the idea of eating back exercise calories came from. I usually don't. MFP will add them in, but you only get the "starvation" warning if you eat fewer than 1200 calories in a day. I see it as an option if I'm hungry/special occasion or something, but I don't think it's a requirement.

It`s not MFP that came up with the idea of eating back calories. You can find it in many diet related publicatios.

It is related to the "save weight loosing speed" that requires a deficit of 500 cal not more otherwhise you enter "starvation mode" and your metabolism is slowed down by the body to survive (your ability to lose weight at same callorie level drops).

On MFP, we usually input our daily activities which it'll estimate as the calories we burn WITHOUT exercising. At most, it'll go down to 1200 calories depending on how much you exercise. But then it's also appears to be a tradition/requirement that we eat our exercise calories as well.

Thus, if person A's job is say, a teacher, and she burns 2000 calories daily WITHOUT exercise, and 2200 calories with exercise, and she wants to lose weight as fast as possible, MFP will suggest her to eat 1200+exercise calories = 1400 calories because she saw on the forum that since she's pretty near normal weight, it's only sensible to lose 1lb/wk.

However, let's say person B (who has the same height and weight as person A) has an office job (so she sits on her bum most of the time) so her daily TDEE WITHOUT exercise is 1700, but let's say when she does exercise, she ends up burning 500 calories for a grand TDEE total of 2200 calories. For her, MFP requires her to eat 1200+exercise calories = 1700 calories.

In this case, we see that both women end up with the same TDEE, but MFP suggests one to eat 300 calories more daily just because of her daily activities.

So why is it okay to eat less if it's our daily activity that's burning the calories, but we're required to eat back our exercise calories? (Also, I know this problem becomes irrelevant when we're only doing TDEE - %, but let's put that aside for now as I've seen many people simply take the approach of eating what MFP suggests plus exercise calories instead of TDEE - 20%.)

If person A or B were to do both methods they would probably find, provided they input their info accurately, that the MFP number + exercise and the TDEE-% to lose the same amount of weight per week are fairly close...at least they are in my case.

1) MFP isn't "allowing" anybody to lose weight faster than others.
2) They are both netting 1200 calories. If you didn't eat the calories back, you'd be under 1200 for the day.
3) Person A would theoretically lose at a higher rate because the deficit is larger.

If that doesn't answer your question, is your real question: "why can't we eat less than 1200?".. because if it is. I'm done here.

If it helps, I can use my own statistics.

If say I input myself as sedentary, anything above 1640 gets added to my calorie intake as exercise calories.

If say I input myself as very active though, it becomes 2040 calories. That means anything above that gets added to my calorie intake as exercise calories.

And let's say I input myself to lose 2lb/week, which MFP will put me at the baseline of 1200 calories.

Well, why does it matter whether I'm sedentary or very active? If I exercise when I'm "sedentary," and not when I'm "very active" I could technically end up with the same TDEE, but MFP will suggest me to eat more if I'm sedentary...which doesn't make a whole lot of sense....

Based on those numbers, there is no way you should be setting your goal at 2lb/week. You obviously don't have that much to lose. Try the same thing but with a more sensible loss. You will see that there will be a difference.

ETA: Furthermore, if "sedentary you" decides to work out for 400 calories everyday, both "sedentary you" and "very active you" would eat 2040 calories (by eating back the exercise calories). Making it the same amount of food and the same deficit.

On MFP, we usually input our daily activities which it'll estimate as the calories we burn WITHOUT exercising. At most, it'll go down to 1200 calories depending on how much you exercise. But then it's also appears to be a tradition/requirement that we eat our exercise calories as well.

Thus, if person A's job is say, a teacher, and she burns 2000 calories daily WITHOUT exercise, and 2200 calories with exercise, and she wants to lose weight as fast as possible, MFP will suggest her to eat 1200+exercise calories = 1400 calories.

However, let's say person B (who has the same height and weight as person A) has an office job (so she sits on her bum most of the time) so her daily TDEE WITHOUT exercise is 1700, but let's say when she does exercise, she ends up burning 500 calories for a grand TDEE total of 2200 calories. For her, MFP requires her to eat 1200+exercise calories = 1700 calories.

In this case, we see that both women end up with the same TDEE, but MFP suggests one to eat 300 calories more daily just because of her daily activities.

So why is it okay to eat less if it's our daily activity that's burning the calories, but we're required to eat back our exercise calories? (Also, I know this problem becomes irrelevant when we're only doing TDEE - %, but let's put that aside for now as I've seen many people simply take the approach of eating what MFP suggests plus exercise calories instead of TDEE - 20%.)

Edit: And I know that both works...but one would end up losing weight faster while the other slightly slower...and 1400 seems a reasonable daily amount so why wait longer for her dream body?

I don't think your numbers are quite right, which would explain the confusion. For person A, if she is getting 2200 TDEE and wants to lose 1lb/ week, MFP would give her 1700 calories (2200-500). If she adds her 200 calories exercise, she gets 1900 caloreis to eat. If person B is the same height and weight but has a sedentary job and her TDEE is 1700. MFP will give her 1200 calories (1700-500) and if she eats back her exercise calories she gets 1400 calories for the day.
So, person A expends 500 more calories per day for daily activities, so she gets to eat 500 more. They are both trying to lose 1lb/ week, so they both are eating 500 calories less than their total avaialble for the day, which is TDEE + exercise (2400 for person A and 1900 for person .

To answer your question, let's look at another example.
We're going to use your people from above -- Person A is the teacher, Person B is the office worker, same height, same weight.
We've already established that in order to meet daily energy needs (TDEE) and lose 1lb/ week, Person A would eat 1700 calories/day and Person B would eat 1200 calories/ day. Now let's look at exercise. If both Person A and Person B work out and burn 200 calories, but Person A eats her exercise calories and Person B does not, we now see a difference in their calorie deficit for the day. Person A has earned a total of 2400 calories for the day (TDEE + exercise) and has eaten 1900, which means that she is right on target for a 500 calorie (1lb) deficit. However Person B has earned a total of 1900 calories for the day (TDEE + exercise), but has now only eaten 1200 calories. So she is eating now eating a 700 calorie deficit, which is actually equal to a 1.4lb loss per week. Maybe that doesn't seem so bad. But let's take it to an extreme. Now both of our people are working out and burning 1000 calories per day. Person A is earning 3200 calories per day (2200 TDEE + 1000 exercise) and is eating back her exercise calories at a total of 2700 calories per day eaten. She is still running a 500 calorie (1lb deficit). In the meantime, Person B has earned 2700 calories for the day (1700 TDEE + 1000 exercise), but is not eating back her exercise calories. She is still only eating the 1200 calories that MFP gave her, so she is eating at a 1500 calorie deficit (which amounts to 3lb/ loss per week and is not in any way healthy).

Short version: MFP is looking at a set level of how many calories it takes to run the body of a person of your height, weight, and activity level on a daily basis and then subtracting a set amount to make you be in a deficit. If you don't significantly change your activity level, the deficit will always be the same. If you do exercise and don't eat the calories, you are adding onto the deficit that MFP has already calculated and, if you exercise a lot, you will keep running the deficit up to an unsafe level. The risk is that you will eventually force your body to try to compensate for all of the calories that it is not getting and your metabolism will slow down. And you will probably be burning muscle as much as fat, which also doesn't help anything.

I hope this helps.

TDEE + exercise

TDEE means total daily energy expenditure. This includes what our body needs to survive on, all activity and all exercise. There is no "TDEE plus exercise".

MFP is NOT a TDEE calculator. It calculates the amount you need to survive on (BMR) then it adds a modifier when you choose your lifestyle not including exercise.

This is why you add extra calories for exercise, they were not included in MFP's calculations. But they would be calculated if you used a TDEE calculator.

I'm not exactly sure where the idea of eating back exercise calories came from. I usually don't. MFP will add them in, but you only get the "starvation" warning if you eat fewer than 1200 calories in a day. I see it as an option if I'm hungry/special occasion or something, but I don't think it's a requirement.

That's something I don't get as well, the 1200 calories thing. Why is it that number? I'm somehow can't imagine our body thinking, "System consuming less than 1200 calories, error error...commence metabolic slowdown..." I mean, wouldn't a person who's burning 2500 calories daily, even if she eats 1200-1300 calories, staring experiencing metabolic slowdown or "starvation"?

It's actually based on scientific research. The current evidence suggests that below the 1200 calorie mark, the average person's body starts to have to compensate for not having enough calorie intake (energy) to perform basic daily functions. This results in a metabolic slowdown which will only hinder your weight loss in the end. If you are interested in reading the biochemistry of how this happens, check out:
http://www.metaboliceffect.com/metabolic-damage/