How to lose weight fast as possible for 20 year old?

Not too fast! To lose weight insure that calories burned > calories consumed. Drink at least 8 - 8 oz glasses of water per day. Aim for at least 5 servings of vegetables ; 4 servings of fruit per day. Use whole grain when possible. Avoid sodas, alcohol ; junk carbohydrates. Get in a good mix of aerobic ; weight lifting exercises.