Reasoning about a maximum 1000 calorie deficit.........

I was wondering if anyone knew the reasoning behind why you shouldn't have a calorie deficit of more than a 1000 calories... I'm not trying to dispute it or argue with anyone because I am really starting to put alot of faith into what some people on this site tells you (note: eating more and lifting weights actually works! YAY!!), I just find it easier to stick to something that I know the reasoning behind.

So again, anyone know the reason why you shouldn't have more than a 1000 calorie deficit in one day?

i don't know, but if i were to speculate, i'd say it's just unsustainable.  you have to eat a lot and exercise a lot to have more than 1000 cal deficit and remain healthy, and unless that exercise is part of your regular work day, at some point you're probably going to falter on the exercise.  then you've created a habit of over-eating.

A 1000-calorie deficit will give generally give you a weight loss rate of 2 lbs per week, which the accepted standard as the maximum amount that is safe to lose per week. I believe that is the magic number because more than that draws disproportionately from muscle mass--but I don't know the science behind that--perhaps someone with more knowledge could tackle that. I agree with pgeorgian, though, that more than that would probably not be sustainable over the long haul.

It has the same effect as not eating enough calories--our bodies are simply not built to run on so much less than what they need. I mean, I doubt that '1000' is that big number that works for everyone (for me I'm much more comfortable at a 500-600 calorie deficit), but it's a good benchmark for the point where your body stops losing weight and instead holds onto fat in starvation mode, because you are simply using so much more than what you're giving your body.

To understand it you have to think about someone who, say, needs 1900 cals to maintain their weight.  If they ate a 1000+ cal deficit they'd be taking in <900.   It's easy to see how someone on that kind of diet would soon struggle with feeling unwell, unhappy, hungry, lacking in basic nutrition, tired all the time or just running out of energy.   If someone needs 3000 cals to maintain their weight because they're particularly heavy or because they do a lot of exercise, they are going to feel exactly as bad as the <900 person if they take in <2000 cals. 

So basic health & nutrition is one reason.  Another reason is that if a body needs 2000 cals it expects 2000 cals.  If it's only given 900 to work with it will conserve energy (fat stores) as best it can by slowing down the metabolism.  That's the 'famine response' or 'starvation mode' everyone mentions and it's a natural, evolved reaction to a shortage of food.   When food becomes available again, the slow metabolism ensures that the extra is quickly converted to fat to replenish the stores.    Anyone trying to lose weight can find they effectively 'diet themselves fat'

So it's pretty much the same as not eating enough calories, your body will go into starvation mode. Well, I guess that makes sense. Thanks!

resurrecting an older post here because I'm curious to know.  I'm 225lbs, 5'5, and I am nursing a baby full-time.  I also do light to moderate exercise 5-6 days per week.  CC says that I burn (on average) abouit 3400 calories per day.  My BMR is a little over 1800 per day.  So in my case, a 1000 calorie deficit would put me at 2400 per day and so I'm thinking theoretically I could do a 1400 deficit and stll be OK?  Since I do have that much leeway.  Granted of course no way will I eat so little as to lose my milk but I guess I'm having a hard time wrapping my head around the idea of eatin 2400+ calories per day.  So, if I understand correctly, even if I ate 1900 calories per day, which would be a 1500 deficit at this point, I wouldn't go into starvation mode?  I imagine I'd probably lose my milk though...  What I'm trying to shoot for is about 2200 per day at this point which gives me anywhere from 1000-1300 deficit depending on how much activity for the day.  Is this safe?  SO basically my question is - is it OK to do a larger than 1000 cal deficit if it doesn't put you below your BMR?

Your body can only burn so many calories-worth of fat in a day.  If your deficit is more than this many calories, it'll burn muscle instead.  The exact number varies for everyone (depending on height, weight and body fat percentage) but keeping your deficit below 1000 should keep most people from crossing over into muscle-burning territory.

If you're having a hard time imagining eating 2400 cals/day, try drinking some of your calories - milk and 100% fruit juice are great ways to up calories in a healthy way.

OK, that makes sense.  I think the hard time imagining eating that much isn't so much not knowing HOW to eat so much but it's the old standby "eat less to lose" thought process and even though I know I burn a lot of calories every day it still goes against the grain for me to eat that much.  I do it, though.  And it's been working so far - 11 lbs lost since 10/19...