Here's my story.....
For the majority of my life I have been extremely physically active... swimming, cycling, springboard diving, and I even taught Step Aeorbics in my early 20s. During my entire age span of 25 - 35 I weighed 165 lbs and had a 30" waist. I am 5' 11" male, so I consider this very healthy.
At 36 I got a job where I spent a lot of time sitting at a desk at work and I started to put on weight. I also drove total 2.5 hrs every day to get to and from work... plus started eating more then I ever had before and exercised less.... then I was laid off work and as a result had a bout of depression... and became extremely inactive because I couldn't afford my gym membership.... pants got tighter... shirts stopped fitting.... so over the next 3 years I gained weight and ended up a painful 205 lbs (owww, my knees).
At 38 I figured enough was enough. That age is a danger zone for many men especially if they gain extra weight since it is more difficult to get rid of once we hit 40. Even though it took a lot of budgeting, I purchased a gym membership, walked into Les Mills classes, and the rest is history.
I started first by reading "Body For Life" by Bill Phillips to fine-tune my diet (I didn't like too much junk food/ fast food/ fried food/ prepackaged foods anyway, I just had to figure out better ways to eat and how to minimize calories). Also the book gave me a great insight to exercising techniques and effective methods to increase results. So my diet was already pretty good, I just needed to kick my butt into gear to regain my health by giving a little effort.
It began with two BodyPump classes a week. Then I added on an RPM class. Then I added on one BodyFlow class to increase my flexibility. Within my first three months the pounds literally flew off... I had lost 20 lbs and weighed 185 lbs... I couldn't believe the change... and as I said, my diet was already tuned up so this was all due to effort alone.
ALSO MAKE A NOTE that I really, REALLY worked in Pump and RPM. Once I got the technique down I LOADED UP MY BAR until by the end of each track, I was literally exhausted. Same with RPM- I was a pool of sweat and open-mouthed breathing by the end of the mountain climb. I knew that only one person was going to get the results for me... and that was ME.
After another 3 more months (6 in total now) I was back down to 175 lbs and a 32" waist. Then I was approached by one of my LMI trainers who was impressed with my efforts and asked if I would be interested in instructing the classes.... and here I am.
It's hard to believe I actually had to drag my butt out to the gym to make just two BP classes per week... that seemed like such an effort at the time. Now I instruct 5 regular classes per week (3 BP, 2 RPM) without batting an eyelash and usually add on one more sub class to cover someone's class, or just do a BodyStep class because I want a little more cardio.
Although I weigh 185 lbs now I am back into 31" pants and I have completely reshaped my body, especially in the arms and chest, which I know is due to BodyPump because LMI programs are all I do in the line of regular exercise these days. I am also mistaken for being in my mid-30s a lot 
Hope my story helps to inspire you and give you a little insight onto one person's journey. 
I really like that previous quote... "Body By Les Mills".... that's what I'm sporting too!
Changing the shape of the world one class at a time.