There is no one answer for "everyone." However, MOST people who have lost a substantial amount of weight and kept it off over the long term do so through both diet and exercise. It is possible to lose quite a bit through diet alone, but there comes a point where you have to start exercising to get past a certain point and still be able to eat a healthy, nourishing amount of food. The more you exercise, the more you can eat. Also, activity keeps your metabolism revved, and strength training will build muscle and make you leaner for your weight. Still, a lot of people start with diet and ease into exercise, so there's no need to go full-bore all at once.
For some good tips on permanent weight loss and maintenance, check out the Maintainer's Forum, both the Living section and the Library.
I have lost weight on both ways: 1) Just diet, but cutting back as I got closer to goal and 2) Diet and excercise
1) I personally found not so great. I found that the closer I got to my goal, I was really only eating rabit food just to see a small loss, and my skin and body looked gaunt.
2) This was much better for me. As previously posted, you can eat a lot more, and it also tones your body (if you use weights). When you build up muscle, you increase your metabolism (ideally turning your body into a fat burning machine) and you find you can eat so much more.
I think I'm about 60% diet and 40% exercise. I've only noticed this because in the weeks I've lost a lower amount of weight it's because I hadn't exercised. I still lost, but when I up the exercise the weightloss is always a little higher.
I was exercising for a couple of months but since my back has gotten worse I have not been doing anything. All though I should be doing something. Anyhow I have lost all my weight with the exception of time above by diet. 1800 calories a day. I am still losing with diet only and plan on making it to goal by diet since I have surgery next month and won't be able to exercise. I know I should exercise but I truly hate it. I am hoping that after surgery I will be able to walk longer periods again. Right now I can only go for a few minutes without sitting. So if I can go walking again I will probably do that for exercise. I'm not much for the idea of going and weight lifting and all that. I just want to get some cardio in so my heart is healthy.
To me the big pluses by adding exercise are that 1.) your metabolism is sped up even after your workout, speeding your losses, 2.) the faster loss helps keep your motivation higher, 3.) your good cholesterol is improved.
Don't forget that lots of water really helps. Not only does it clear toxins, and make the body healthier, but I found that it is true that for years I'd mistaken thirst for hunger. Because of finally learning to drink enough water, I don't feel the need to eat as much.
Personally I'd say 65% exercise, 35% diet. My diet has improved, but it's nowhere near as controlled as some peoples. I often see people looking in amazement at the amount I've lost and the amount I eat. But that's because I eat decent amounts of healthy stuff, and I burn a lot of it off through exercise.
I just started about 2 and a half weeks ago but have lost 4 pounds in that time. What's helped me is definately the exercise and drinking loads of water. I haven't really been counting calories although I do keep track of them and what I eat. I have cut out all the really bad junk foods and soda and kool aid I used to drink. Definately to add to all that is support! I don't think I could have done all this and have been keeping with my plan without my family supporting me and getting excited over my little losses, my diet buddies, and everyone here on the forums!!
Wow.. that last bit sounded like I was accepting an award or something! haha
I am the same as YP1 (again!) - I am about 65% exercise, 35% diet. I've lost 53lb since Jan 1st. I know I could have lost more if I'd been alot stricter with my diet, but I am happy with my loss so far and will tighten up my eating as I get nearer to goal. Obviously, I am dieting and try to stick to 1600 cals a day, but I am not that strict and find that I'd rather workout hard at the gym 5-6 days a week than watch every single calorie here and there!
Dieting alone is okay, but exercise will completely change your shape and fitness.
I'm with YP1 and Amanda Panda with about 70% diet, 30% exercise. I started opposite most other people by exercising first and not making many changes to my diet, but I quickly realized that I would lose, but it would be at a snail's pace. Once I changed my diet the pounds started coming off really quickly.
I definitely know people who have lost without exercise, but since I'm in this to be healthy in addition to looking fabulous, I definitely wanted to incorporate some daily exercise into my routine. Turns out I thought I hated it but now I love love love working out, especially weightlifting.
Plus, most people (well, especially women -- you're lucky, Howie!) really do have to cut back their calories in a draconian way to lose if theydon't exercise. I love food to much for that.