It was a combination of mainly a LOT of cardio (meaning DAILY) with a committed diet. I don't say strict because I was eating wisely, not starving myself. It is about retraining and habits, and that "takes" in about a month and will stick long term if you let it. As with any weight loss, when you cheat you only cheat yourself. I was motivated to stick to it because I wanted to transition quickly, and I knew that I wanted a new body and to make the best of it that I could. What I will describe is what I did for me, but everyone is different.
With my body changing as much as it was, and rebuilding, I felt it was unwise to distort my diet nutritionally one way or another, but I did cut back calories and lowered any fat intake (though it's unwise to eliminate it). I concentrated on making the most of what I allowed myself. Some of that is just eating properly, meaning dropping empty calories (or comparatively empty) such as sweets, baked goods, and simple carbs, and switching to "packed" calories. Pasta went out as did most breads, rices, pizza, fries, potatoes and all. No chips of any sort (carbs, fats, sugars, and salt). I cut out all added sugars (even in tea), and read all the label of anything I did buy that was packaged. Not 100%, as I did go out or did take away. I'd have a part of a pizza once in a while for example. I could eat a little cake or whatever once in a while. You can't feel deprived, or you will resent the diet. I just removed these from my house and my daily diet, and eventually I forgot about them. I went for lean proteins, like chicken, very lean red meat once in a while, a lot of eggs or egg whites (which ended up as omlettes and types of meatless and low cheese frittatas). I would have fish once in a while, grilled salmon, but I am not a big fish fan. I cut back on full cheeses (not 100% eliminated, but in small amounts). I also used a lot of plain non or low fat greek yoghurt, which is high in protein and also calcium. I used olive oil in small quantities. Dark leafy veggies (tons of spinach), peppers, onions, garlic, tomatoes. No beer (but that wasn't hard as I don't really drink it, and I grew up around good beer). I did drink wine, but generally only on weekends (I come from a wine drinking family, and it was a cultural fixture), and my rule was one bottle in the course of a week.
I decided not to skip any meals, just to control what I ate and try to make it appealing and filling. Breakfast was along the lines of: one serving of oatmeal (and actually it was steel cut or whole oats 1/4 to a cup of water. That's a little gruelish for most, but it was a calorie count and oatmeal is very filling as is oat bran) with about the two eggs worth of egg whites in a omelet (which would be full of veggies, such as onions, peppers, spinach etc). Sometimes it was just a bowl of GoLean. I happen to like berries, so it was always a bowl of blueberries or strawberries or a mix. I generally did wraps at lunch using a whole grain wrap no more than 80 cals, with turkey, chicken, lean ham, or egg whites (I added yogurt and oat bran sometimes), then seasoned various ways, with tomato, onion, and spinach leaf. Sometimes I did a grilled chicken salad. Dinner was lean meats or omelets, with veggies. If I needed a snack, it might be a handful of almonds or a slice of turkey and ham, or a slice of herbed chicken etc. I allowed myself a small amount or dark chocolate, 60% or so. I ended up using dark choc chips, and just a few. I had to be careful because, well, it was chocolate.
Some of what I did was also to make sure I ate good food, in modest portions. I have always cooked, so I knew how to make something I would want to eat. That's important, because if you don't enjoy the food you allow yourself during a diet you won't keep to it. Still, I kept it very simple, lots of chicken (but prepared a dozen easy ways using spices, not pastas and creams sauces etc.) I found it was a good time to get creative in the kitchen -- besides, it a great skill to have, it's cheaper than eating out and it impresses the guys...
Another aspect was portion control/serving. Know what you are really eating and what's in it. The first time you make something, measure and calculate what a portion or serving size is, don't guess. You really only have to do it once. I have an eye for measurements after so many years cooking, but I never cut that corner as it helped keep tabs on my calorie intake.
Also: not all calories are equal in the sense of where they come from. Your body uses more energy to burn proteins than carbs for example. I could safely increase lean protein calories if I needed, as they tended to have less effect on my body than carbs do. You can do some research on all that and figure out what works for you. Much of this is about individual metabolism, and how you can influence it. It takes some item to reprogram it, but you can. Supposedly your body changes metabolism in the course of a seven year cycle anyway, you are just playing with that! That's also true about exercise. Cardio isn't necessarily burning more than strength training, but if you want to cut muscle bulk, don't do much training until your muscles stop shrinking. You do want to tone, but you can do that isometrically as well.
