Losing weight

I'm in a contest to lose weight over the summer (June 1 to Aug. 31) and am competing against an unknown number of others around the country. It's through my workplace O'Reilly's Auto Parts and the winners are determined by % of weight lost, not total pounds lost-so I guess a lighter person could lose fewer pounds than a heavier person and still win, just as long as their % is greater. I started at 316 pounds and hope to lose about five pounds/week to end up at around 250 pounds by the end of the contest. If I could do this, I would have lost about 20% of my body weight, which is a pretty good effort. My strategy so far is to walk for about 30-40 minutes in mornings and evenings, eat as little fat as possible (no fast food), mostly eating things like soups, lots of veggies/fruits. I think that I'm on track so far as my weight after 1 week is 310. So I've lost about 6 pounds after the 1st week.