Official MapMyRun.com Community Group: Why am I not loosing weight?

If you are eating exactly the same amount of calories, healthy food or not, you should lose some weight because you are burning more calories if you are exercising more than you used to.  A 3 - 4 mile run burns approximately 300 to 400 calories depending on your weight.  The heavier you are (the more muscle you have) the more calories you burn.  A plain bagel with nothing on it is about 300 calories so if you are eating an extra bagel or extra food after you run, you could be just breaking even.  They say it takes about 6 weeks after starting a new exercise program for beginners to start building muscle.  Their bodies are just becoming neurologically more efficient when they first begin muscle building exercises.  I think my advice would be to give it more time and make sure that you're not eating too many extra calories because of your runs.  Don't give up, it only gets better.  Good luck!

So I have gained and lost 50lbs 3 times in my life.  I'm on the thin side now and am 38 so I'm kinda hoping to stay thin this time.  Anyway,  The only way I have ever been able to lose weight is to count calories.  There are several free tools that will help calculate your required calories to maintain your weight.  Once you know that number, you have to to eat less than that.  1 lb = 3500 calories, so if you want to lose a pound a week you need make sure your weekly calorie intake is 3500 calories less than you need.  Eating high fiber low fat foods and spreading your daily calories out evenly through your waking hours will help speed your metabolism keep your body from going into "storage mode" a.k.a. making fat.  You should add some weight training to your running (2 days week for 30 minutes is enough) to make sure your not losing muscle.  The more muscle you have the more calories you use in a day, if you lose muscle you will have to reduce your calorie intake to keep losing weight. Actually you need to reduce calorie intake if you plan on losing more than a little weight.  I found that number for me is about 100 calories per 10 pounds of fat.

Hope this helps, good luck and keep running!