Being slim does not equal to being fit
But, if you want your physical activities to reach performance level, being slim and trim is a by-product

I was a runner for a few years, starting from competing 5k to marathons
Although I put in honest effort to train, my weight always stopped at a certain point and just would not drop anymore
From all the races I had attended, I noticed that people in the front of the pack (the fast runners) were almost always very slim and lean (both men and women), especially long distance runners
Sprinters and 5K runners some may be muscular but never half marathon, marathon, ultra, and long distance trail runners who are in the front

The further back you are in the line of runners, the more body fat you see
I would not call most of them fat, especially marathon participants, because without training, one can't do a marathon comfortably (doesn't matter if you are 18 with a body not abused).

Based on my weight and experience, I could not figure out why I wasn't able to look more like those lean runners

After 9 months since I started hiking, I finally realized why my weight as a runner got stuck
I was simply eating too much, eating the wrong kind of food, and eating at the wrong time

The body is like a car, a machine that runs all day, even during sleep
If you bought an expensive car that the instruction menu says to use premium fuel, you would not try to save a few bucks by pumping the cheapest gas you can find and often leave the tank empty, right?
The same theory goes into fueling the body, which is a fine and precious machine.
If you put junk into it, not feeding it when its empty, you can't expect it to perform at top form.

I did not understand this when I ran therefore my weight got stuck and my performance never improved after a certain point.

From hiking and having time to listen to my body and start in earnest to revamp my diet, I was finally able to drop the weight (ever since 12, I have never weighted this low) and able to hike with ease (carrying extra weight while climbing a peak is NOT fun)

Now I enjoy clean and healthy fuel
Not once I crave sugar, fried food, or salt since I started cooking my own meals
My taste naturally gravitates towards food that provides nutrition and energy my body needs
Even when I  did hard/long hikes or backpacking (carrying 30 to 35lb) I never once used the exursions as excuses to eat junk

After Rim 2 Rim on Saturday, I swore I lost 3lb from the deficient calories and sweating!
My pants got looser in the waist and my feet shrunk!
However, after I got back to my camp site and pitched the tent, as hungry and tired as I was, I still managed to cook up a pot of oatmeal mixed with dried pork and diced pickled turnip root as my post workout fuel/dinner (complex carb, protein, and electrolyte)

Not eating is not an option after the workout
Not eating healthy is not even a choice

If you have been working out but not losing weight/fat, start a food diary and you will see why
Only by exercising and eating healthy (right food at the right time; not one big meal a day) can a person lose the weight successfully and keep it off permanantly

After losing 40lb since December, I am a living testimony.