Gain weight while working out and eating healthy?

This has always boggled me. A few months ago, when I was slacking and didn't work out for about a month, I was down to 103 (I'm only 5'1"). Now I'm back into my routine, training for a half marathon, strength training every other day AND eating healthy, I'm up to 107. I'm confused. Now people always tell me not to pay attention to what the scale says, and to go off how I look and feel, but the fact that I'm gaining weight is annoying me. Is anyone else having this problem?

EDIT: You could just be replacing "fluffy" fat with lean muscle, so if your measurements are getting smaller I wouldn't worry (muscle fits into a smaller "container" than the same amount of fat), but, if you are actually gaining weight, getting bigger, it could be because you're not eating enough.
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Oh yes, I had that problem! I gained a "mystery" 15 lbs. over 18 months, and I work out 6 days a week. The more I gained, the more I restricted food. And I gained more. People didn't even believe me. They thought I was binging in secret or insisted I must have some mysterious illness. What gives?

Starving your body, slowing down the metabolism, failing to provide fuel (food) for workouts on top of basic functions (living) is like an energy company not having enough electricity for the whole city -- they have to do rolling brownouts. Something's gotta give, so it's your metabolism.

Keep doing this for too long and then every time you have a little something extra -- even just 1 special dinner out -BOOM! the scale goes up. And it doesn't go back down.

Interestingly (and to add to the confusion), I would occasionally have a trip where I couldn't workout, or some short period of time without working out. I would instantly lose weight. Why? I was so confused!

Here is a post of mine from another similar thread; I hope it helps:

OK. I'm gonna give this a shot. I am an avid lifelong athlete. I have never been overweight, however, I used to eat too few calories (without knowing it), and a couple years ago, I actually GAINED weight bc of having slowed my metabolism to the point that every little extra treat I ate caused a weight gain, even though overall my calories were too low. THIS DOES HAPPEN.

It is also the reason so many fat people stay fat. They restrict their calories so low, slow their metabolisms, binge (even a little), gain weight, restrict more . . . . and so on and so on. But they are still fat.

It is also the reason most people can't lose that last 10-20 lbs. For real.

1. MFP has a deficit built in. Let's say you're trying to lose 1 lb/ week. That is a 500/day deficit from your BMR (the amount of calories your body needs to complete basic functions.

2. You exercise and burn 500 calories. Now you are at a 1000 deficit. If you eat back those 500 exercise calories, you refuel your body and you still have a 500 deficit for that 1 lb loss. If you DON'T eat back those calories, you have too little fuel. This is bad. This is too much of a deficit for basic functions. If you do this for a long time, you will STOP LOSING WEIGHT. Why? bc your metabolism will slow down -- it's like a brownout--not quite enough electricity to make the whole city (your body) run, so it has to slow down some things. You will probably start being tired a lot, your skin and hair might start to look worse, and you might even gain weight. But you might NOT be hungry -- your body is getting used to fewer calories. That's bad.


That's when you start to gain weight. Let's say you're running along, eating 1200 calories a day, and exercising 400 calories a day, so net is 800. You're losing, you think this is great. You keep doing it, but after a while you stop losing. hmmmmm. One weekend you go out to a special event and have a slice of pizza and a beer. 1 slice of pizza and 1 beer. So you ate maybe 2000 calories that day and exercised off 400, so net 1600. BOOM! You gain 3 lbs! What?!

Next, you freak out and restrict yourself down to 1000 calories a day and work out extra hard, burning 500 calories. Great, netting 500 now. You don't lose any weight, but you sure feel tired. Better get some red bull.

Are you getting the picture?

EDIT: When you work out, you need fuel. Food is fuel. If you don't eat back those exercise calories, you will not only have a big calorie deficit, you will have an ENERGY deficit. Remember, the calorie deficit for weight loss is built in when you use MFP. Exercising basically earns you more calories because you must refuel.
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There are many people who will tell you not to eat exercise calories. Before you take their advice, you might want to see whether they are at goal, have EVER been at goal, or have ever been able to maintain at goal. If anyone says to you 'THE LAST TIME I LOST WEIGHT", just stop listening right there.

Ask some athletes whether or not they replenish their bodies with food equal to the calories they burn. Ask people who are fit and have achieved and maintained a healthy weight for some years. Don't ask people who count walking across a parking lot as exercise.

Here's an interesting case study about how to stay fat while consuming only 700 calories a day. Take a moment, you'll be glad you did:

http://www.myfitnesspal.com/topics/show/3047-700-calories-a-day-and-not-losing

blessings.