I find this topic very interesting: Does food or exercise most influence fat and weight loss? Can it be either/or? Do they work together differently, and how so?
I don't think that there is a single answer for every person, but I know that managing my food intake is the 98% for me. This has been proven time and again during the years that I have lost almost 150 pounds (and regained and lost some of those over and over again). If I want to see a signifcant reduction in my weight, I need to make sure that my food intake supports that goal. Whether it is Weight Watchers or calorie counting or a strict food plan like the 17 Day Diet that I am currently following, food determines if I lose weight or not.
But exercise is not unimportant to me. Not only does it enhance fat loss for me as I build muscle, but it reinforces my commitment to my food plan. After a 30 minute run, I find myself unwilling to trade the effort for junk food or other treats. It makes me more aware of the trade offs of my energy expenditure, and also provides me with energy (after the initial adjustment period, of course) and a sense of pride and satisfaction that keep me focused on my goals.
I have seen many people I know refuse to change the eating habits that made them obese in lieu of embarking on a very demanding exercise program. They may experience some results in the early stages of the changes, but I have then heard the complaints that they are not losing weight as they had hoped. Yes, muscle is being built and they are becoming fitter and healthier in the process... all wonderful and healthy changes... but the obesity persists. People can run marathons while obese because they have built endurance and fitness, and they can be quite healthy despite extra pounds. It all depends on the goals of the individual, but weight loss is not guaranteed from a change in activity alone.
I am sure that there are anecdotal stories of people who state that they lost massive quantities of weight while eating anything and everything they want in massive quantities with only the addition of exercise, just as people lose massive amounts of weight with no exercise. I do not personally know any of the former type of people... at least not any that have maintained the body composition change in the long term. Most of the people I know use them both synergistically, but the changes in diet lead the way to major changes in their body weight and composition.
Interestingly enough, I was watching WGN News yesterday morning and saw Matthew Mcconaughey discuss losing 40 pounds for his recent role. His experience was that exercise was only 2% of the contributing factor for it. Once he cut his food intake down to approximately 1800 calories of healthy proteins, green vegetables, and fats, he saw the results that he desired, even without exercise due to an injury. And this is from a man who was fit at the start of the process.
For me, I need to include both food control and exercise in my weight reduction and body composition endeavors, especially to set the groundwork for maintenance once the weight is gone. But there is always something to learn when it come to this because I think it is an art instead of a science due to our individual bodies and their differences (spoken by a woman with no large intestine!).