1. Program your brain.
Write out a goal statement and read it out loud at least twice a day. Spend at least 5-10 minutes a day visualizing yourself having lost 20 pounds. Feel the incredible sense of accomplishment and pleasure that comes from achieving a big goal.
Do the above for at least 21 days and it will become a habit that will build unstoppable momentum!
Note: The main goal here is to build a burning desire to lose the 20 pounds fast. Try to think about your weight loss goal constantly. Surround yourself with photos of people with great-looking, fit bodies. Watch motivational videos on Youtube every day. Don't discount this stuff... it works and you need to do it!
2. Do a fat-loss jump start.
Do a 1 or 2 day juice fast and/or raw diet. For a 24 hour period consume nothing but spring water with fresh-squeezed lemon or lime juice (preferably organic). The next 24 hours you can continue the juice fast OR you can do a 1-day raw diet. For 24 hours consume nothing but raw fruits, vegetables, nuts, seeds, and spring water.
This "jump start" diet will help to flush toxins out of your body, "reset" your metabolism, and boost your energy. You will also likely lose a couple of pounds. Obviously this works best when you can stay home, such as a work-free weekend.
Note: During this time you may want to take a half hour and clean out your kitchen. Put all the junk foods, candy, sodas, etc. in boxes and bring them to a local charity.
3. Eat a paleo-style diet.
Base your diet around the foods the human body is designed to thrive on: meat, fish and seafood, eggs, fresh vegetables and fruits, nuts and seeds, and good fats (virgin olive and coconut oils, natural nut butters, avocado, etc.). Limit your intake of starches (especially grain products, white rice, and white potatoes) and dairy products (except for low-sugar yogurts and kefir).
After a couple of weeks you can begin to rotate/cycle your intake of starchy carbs in a way that keeps your metabolism off-balance and burning fat.
Avoid almost all processed foods, especially refined sugars, flours, and fats!
4. Do short, intense, metabolism-stimulating workouts.
Focus on doing 20-40 minute workouts that involve short bursts of high-intensity exercise followed by periods of active recovery. High-intensity interval training (HIIT) is one of the best examples of this type of exercise. Another is full-body strength training involving several "circuits" made up of sets of "compound" exercises (e.g. squats, pullups, pushups, situps, etc.).
This type of "burst" exercise is a proven fat-burner and metabolism-stimulator. Besides burning tons of calories, it causes your body to product powerful steroid-like hormones (such as human growth hormone/HGH) that burn fat while protecting vital muscle tissue and maintaining a healthy metabolism.
Try to exercise 4-5 days a week, with at least 2 days of rest. Creatively change your workouts constantly to keep your body from adapting. Routine and boredom are your great enemies!
Note: One day a week your workout should be 40-60 minutes of playing your favorite heart-pumping sport or activity. Bike riding, swimming, rowing, playing basketball, tennis, soccer, or volleyball, hiking, and climbing are all good examples of great fat-burning activities that many people really enjoy. If you don't currently do any of these things, now's a great time to learn at your local fitness or community center!
5. Take the BIG 3 diet supplements.
Whey protein powder, omega 3 fats, and a quality multivitamin. If you're eating the kind of natural, healthy diet explained above those 3 supplements are the only ones you should take... mainly because they'll help you recover from intense exercise faster. The whey protein, especially, is an extremely useful "wonder food" that does all kinds of good things for your body and health. The omega 3's and multivitamin will ensure that all your nutritional "bases" are covered.
Well... that's it: the steps to take to lose 20 pounds very fast. Do them all at the same time and you'll lose pounds of fat within just a few weeks.
Good luck... now get going! :-)