Why Eating Exercise Calories is so important.

I love this information and it makes a lot of sense to me, I usually eat back over half of my exercise calories.
One question though,
When I complete my diary for the day and mfp says "If every day were like today... You'd weigh ..... kg in 5 weeks
I have noticed that on days when I have eaten them back, the projected weight loss can be up to 1 kg LESS, than say, the day before when I did not eat them back.
This little prediction tool has kept me confused regarding whether or not I should really be eating them back all the time or not, is the predicted weight by mfp accurate or something to ignore?
Thanks

I often hear people asking why eating your exercise calories is a good thing?
These people think 'That's extra calories burned, so that will speed up my weight loss.'
Well, yes and no.

The thing is, your body needs fuel.
Your metabolism, typically around between 1200 and 1800 calories, are the calories that your body will burn, during the day, every day. Even if you sat around on the sofa, or slept, or were in a coma. You would need this to allow natural processes like hair/nail growth, skin replenishment, organ function, etc to continue.
That's why it's very dangerous to eat anything under 1200 calories!

So, lets take the average 1500 calorie metabolism.
- If you live a sedentary lifestyle (desk job or no exercise), you would probably only burn 300 - 500 calories in a day by moving around. So you need 1800 - 2000 calories to maintain.
A significant amount of the population leads a sedentary lifestyle, so most doctors recommend 2000 calories a day is good.
- If you live a lightly active lifestyle (job involving some walking or some exercise (1/2 days) then you'd burn around 500 - 700 by moving around. So you need 2000 - 2200 to maintain.
- If you are quite active (some manual labour or exercise 3 - 5 days/week) then that's probably 700 - 900. Thus, you need 2200 - 2400 calories to maintain.
- And if you are very active (manual job or exercise 6 - 7 days/week) then you're burning around 1000. So, you need about 2500 calories to maintain.

This is your Total Daily Energy Expenditure (or TDEE)

MFP will set your deficit at what you want 0.5/1/1.5/2 lbs/week or -250/-500/-750/-1000 calories below your TDEE.

Simples, right?

Well, ish. Let's take an average scenario:

--

Meet Jane. She weighs 200lbs, and wants to lose 50lbs.
Jane has a metabolism of 1500. She leads a sedentary lifestyle, so she burns about 2000 calories per day.
Jane wants to lose 1lbs/week

MFP calculates Jane's calorie intake and deducts 500 calories. She will require 1500 calories to lose 1lbs/week.

But Jane decides she will start running.
Jane burns 400 calories when she runs for 30 minutes.
She does not eat back those 400 calories.

Jane is now NETTING 1100 calories.

*NET = Calories Consumed - Calories Burned from Exercise
You're NET should equal your CALORIE GOAL to achieve weightloss.

Because of the extra activity, 400/1500 of the calories consumed have been burnt by Jane. That means the body must function on only 1100 calories per day to allow natural processes like hair/nail growth, skin replenishment, organ function to continue.

THUS, Jane's metabolism drops* to meet her NET calories (1100).
NB* This may take several weeks and will not respond to occasionally high deficits.
Over the same period of time, Jane's body will respond to the huge caloric defecit and try to preserve the body, by burning Jane's muscle rather than her fat. The number on the scale drops, but Jane does not seem to get any skinnier.

Now she burns 1600 calories on sedentary days, and 2000 calories on exercise days.

When Jane has lost 50lbs and returns to normal eating, she can only eat 1600 calories on sedentary days or she will gain weight again.

HOWEVER. If Jane decides to eat back the 400 calories:

She continues to lose 1lbs/week
Her metabolism will increase because (a) she is exercising (which increases the metabolism) and (b) because she is eating 1900 calories (the more calories she eats, the more her metabolism is raised.)
However, her NET calories remain at 1500, so she achieves ideal weightloss.
When Jane reaches her goal of 150lbs, her metabolism will be faster so she is able to eat more than 2000 calories to maintain her weight.

--

Do you see? But eating back her exercise calories, Jane is able to continue her weightloss without damaging her metabolism for the future.

Exercising and then eating back your calories is just about the best thing you could do for your weightloss. It raises your metabolism, allows you to eat more, and helps to tone/build muscle rather than burn it so you don't get that flabby look of loose skin.

I really hope this helps someone.

OP is my new best friend.