Do people literally run themself thin?

Combined with a decent diet, yes, many people have done this.  I'm sure you'll hear lots of stories here about folks who lost umpteen pounds by training and eating right.

Many can lose some weight by just eaing better, or by just exercising more, but the two in combination are more than the su of the parts.

Briefly:  weight loss isn't brought on so much the calories that you consume while running -- most of us replenish those pretty quickly.  Rather, the weight-loss benefit from exercise seems to come from the fact that the exercise keeps your metabolism boosted.  Without it, your body will tend to suppress metabolism when your caloric intake goes down -- its way preparing for what seem to it to be impending lean times, so to speak.

Warning:  it is difficult to have absolutely top quality workouts while you are losing weight, because the caloric deficit tends to make you tired.  This doesn't mean you can't run; it just means you might not be able to do that 6x1200 LT intervals workout as strongly as you hoped...

It is just like anything else.

More calories out then calories in = weight loss.  It may not be the fastest way to lose weight, but it is easy to do over a long stretch.

I went from 230-ish in '04 when I finally got back onto a bike and road around 1,300 miles that year.  Then the next year I pretty much only ran and trained for a marathon.  By the end of '05 I was back down to the mid 180's.  So 50 pounds in a bit less than 2 years by just cycling and running.

Now at peak events when I'm training hard I can see as low as 169 or so.  My ideal is 175.  All done only by S/B/R.  I do not do any weights or any other alternative training.  And I eat like crap most of the time (like my 1,200 calorie Fajita Burrito from Chipotle I had for lunch today). 

I know my question sounds crazy. But I intially started thinking about it after I heard a colleague say it. Now it's been stuck in my head.

I guess I really don't know how to explain it...

i think it was Rick/Daremo  that already said it but it's all about calories, I gained weight training for marathons since I thought I could eat more. So until I started stepping on the scale I was running myself fat, 

It doesn't mean you need to starve yourself but it you burn more than you take in you will lose weight, and over a period of time, (seconds.minutes) you will lose weight

A bit off topic, but I talked to a coach who coached a number of couples training for IM. They trained together and ate mostly the same food. In this coach's experience the men lost weight and women actually gained weight.

I followed the training of lots of BT women this past year that were training for their first IM, I wouldn't say any of them easily lost weight..most struggled and wanted to drop a few pounds but most didn't get to where they hoped to be.

Yes, I have done this but it takes more running than most people do. I didn't see the effect at all until I was consistently running 50+ mile/week. Over the course of about 6 months I lost 20 pounds without changing my eating habits at all. It works out to just less than a pound a week, so it's not rapid weight loss, but weight loss was not really a goal of mine - it was just a byproduct of what I was doing.

I don't know if there would have been a point where the weight loss stopped because I stopped running so much for a few months and gained some back. In recent months I have once again ramped up the mileage and the weight is decreasing once again. I now have a (hopefully) short term injury, but should be able to resume my higher mileage running in a few weeks.

Last year through the consistent higher mielage running I was able to get through the entire holiday season without gaining any weight - in fact I lost weight despite not changing my eating.

However, if you're looking to lose a large amount of weight quickly this approach may not be the best - especially since running this much would be very difficult for a very overweight person. I would suggest utilizing the bike primarily until enough weight has been lost for higher mileage running to even be attempted. About 8 years ago that's what I did and I lost 50 pounds in 4 months. However that still required a substantial committment to both biking and dieting as I biked about 150+ miles/weekly, and combined it with a lower calorie diet.

I'm a weird case...when I train I crave healthy foods, and when I don't train I crave weird junk stuff.  So, for me to loose weight I have to train (run, bike or swim). 

x2 - I have to keep up a very busy regime of working out OR ELSE....Flaming Hot Cheetohs with Lime start looking really good!!!!

PennState - 2008-11-25 5:46 PM Using my example (of running close to 200 miles a month) I put 12 lbs on from my IM weight, so it is possible to run yourself NOT-thin

Damn Fred, what the hell are you eating???

At the peak of marathon training is when my wife starts to get REALLY upset with my training because I'm so thin .......

PennState - 2008-11-25 5:46 PM Using my example (of running close to 200 miles a month) I put 12 lbs on from my IM weight, so it is possible to run yourself NOT-thin

And this was exactly my point to her. I've been at this too long and know too many "runners" who typically gain weight especially when training for marathons. (we were talking about my running).

 I tried to "discuss" her theory, but you know those people who just don't hear you.

 personally, my body is responding to the running yes. But I'm no fool. I know I have to watch my food intake and add in some other activity to finish with my weightloss.

She just made me so mad. First, commenting on me...then by not hearing me out.

I went from a size 10 to a 4 in 8 weeks, most will say too fast, but it worked for me.  I'm stiill at the same 4 over a year later.  Probably 90% of my fat loss came from following a nutrition plan to the letter, not from the exercise.  However a$$ whooping workouts made me WANT to stick to that nutrition plan.  Each day I had a little less weight to carry.  I just kept thinking about 10 lbs. being close to the weight of a gallon of milk.  I do not even want to run 1 mile carrying a gallon of milk, let along 5 or 6 miles.  Hence, motivation to keep my nutrition tight and keep it off!

You're doing great!  All about finding out what works for you....then stick with it! 

Agree with most of the posts above. Especially in that running boost your baseline metabolism if you train enough - you will tend to naturally eat the same amount of calories you burn otherwise.

In the NOVA PBS special, 12 non-runners were trained over 6 months to run the Boston marathon. In a midcycle test, all of them had nearly doubled their baseline VO2, lactate threshold, and other measures of physical performance. But almost everyone's weight was stable, except for the one large lady who was actively dieting on top. 

Ironically, it may be easier to lose weight faster by not training and dieting hard. (This is almost definitely not healthier though, and not a preferred method for good health.)