[JudoSam]

you have to remember the two basic rules of health.

1. you cannot out exercise a bad diet
2. you cannot out diet a lack of exercise

yes, you can lose a few pounds with just diet or just exercise, but it will be short lived. most likely, you will gain it back, and then some. also, you aren't losing 20 pounds and then going back to doing what you were doing before. you have to view this as a lifestyle change. once you get to your goal, you're looking at about 50-75% of the effort it took to get there to maintain it.

as far as your diet goes, kill the junk food and get the bulk of your carbs from fresh fruits, vegetables, and nuts. keep your protein intake high, but avoid "protein enriched" junk. fish, chicken, lean red meat are where you get your proteins.

as for exercise, if you aren't sweating and out of breath, you aren't exercising. a good 30 minute exercise routine will make you feel like you need a shower. cardio is great, but you have to build muscle mass. you build muscle mass with lifting weights and body weight exercises (push ups, pull ups, squats, etc). don't worry, unless you're in the market for anabolic steroids, you aren't going to get big and bulky. what will happen, though, is that you will gain some muscle mass that will burn calories while you are sleeping, and keep weight off while you are in the maintenance phase after reaching your goal. you should be doing cardio 3 times a week, and lifting weights 2 times a week.

finally, keep your goals realistic. i have cut 20 pounds in under a week for wrestling and judo tournaments, but it goes right back on the day after weigh ins. lasting weight loss happens at the rate of 2-5 pounds per week, depending on your weight. anything more, and you are either just cutting water weight, or you are losing muscle mass.

source: i've been an athlete/trainer for my entire life.