Not eating enough

MFP is set up so you lose your goal amount of weight wether you workout or not. So if you don't workout and eat 1200 cals you will lose your goal amount. This is the same as eating 1600 and burning 400 from working out it nets 1200 (1600-400 is the same as 1200-0) So you must eat the exercise calories in order to reach your goal. Otherwise you may burn more or less, but not you goal.

1200 calories a day is not very much and if you are exercising sufficiently (this depends on your body type and fitness) you could be getting as little as 600 kcal net/day. Think about your body as an engine. If you put 5L of gas in and then drive until it until you are running on fumes... eventually the car will stop. Now imagine that those fumes are all of your nice new muscles! Your body will consume muscle and convert it into fat if it does not have enough energy. Calories are converted into heat. No calories, no heat, no energy.

Use exercise to build fitness, stick to your 1200kcal (net) diet plan and see where it takes you.

MFP calculates your daily goal after taking into account the deficit required to lose a certain amount of weight a week. You should be aiming for 1200 a day...no lower than this. Your body needs food, nutrients and vitamins to psychologically and physiologically function. When you withdraw these calories your body notice this. Eating less than 1200 for a long period of time may also cause your body to hold onto excess weight in fear that you are going into a period of starvation.

Many people do not lose weight eating less than 1200 and find that weight loss begins when calories are increased.

You can choose whether to eat your exercise calories back or not.

There are sticky threads in some of the forums if you still needs things clarified.

That's a misconception that a lot of us has had until we started the process ourselves. Just remeber: YOU HAVE TO EAT TO LOSE WEIGHT!! In doing research on this question, I've read that if you starve yourself, you won't lose weight because the body is going to think that it's not going to get fed and hold on to the fat that you are trying to lose. You have to eat fat to burn fat. It sounds funny, but this has been said on the Biggest Loser, Celebrity Fit Club, and any other weight loss shows that I've seen. You can't starve yourself!

when u set ur goals on mfp, it already gives u a calorie defecit, which when u exercise increases to an 'unhealthier' level therefore, u shud eat bak at least 1/2 - 2/3 of ur exercise cals to compensate.

generally if u wana stay under ur total cals for the day leave around 150-200 which wont give u the 'starvation mode' warning

hope this helps
best wishes
Kirstie xx

Do a search for eating back your exercise calories - it's a subject that has been beaten to death, debated, re debated, and talked about to debate again. The bottom line IMHO - if Yes it's the right thing to do, No you aren't ever going to convince some people that they should, no it's not necessary, yes you may slow your progress or go into the dreaded "starvation" mode, etc etc etc.

Also be aware of what cw454 is saying. When you don't put enough calories in, your body holds on to what it has even harder to increase survivability. Eating healthy instead of sparingly can make the difference between weight loss and sitting at that wall for a while.

Edit: Lol, it's weird refreshing the page and seeing 60 new posts before yours.

Yes. If you only eat 1200 and burn 600 would be like eating 600 and not working out. MFP gave you 1200 NET to reach your goal loss/week. so if you burn 600 you would have to eat 1800 to net 1200 (1800-600)