What is the best way for me to lose body fat? Just excercise? Just diet? Both? Which exercises? What has worked for you?

I am in construction, 40, have a 29–30 inch waist, and am in pretty decent shape. I do have some body fat, which I am sure is mostly due to diet, and, or age. I walk an average of 15,000 steps a day at work (pedometer), and am fairly active even after work. I eat a fairly healthy breakfast and dinner, but lunch is usually fast food, mostly because everyone I work with goes out every work day for a fast lunch. I can’t really run because of past broken ankles, but I can do other activities just fine. I am not “fat”, but I miss the days when I was 7% body fat. What have any of you tried tht worked well? Thanks!