Originally Answered: Who can give me good advice on how to lose weight fast?
Losing weight by the summer should be no problem, provided you have a few things.
1. You actually have weight to lose. A lot of people are not overweight but they think they are, so they try to lose weight they don't have. This leads them to fail at losing weight and a vicious cycle ensues. Check your BMI at http://www.nhlbisupport.com/bmi/. If your BMI is over 25, you may actually have some weight to lose.
2. You're ready (I mean truly ready to the depths of your soul) to change whatever behaviors are causing you to be overweight. If your problem is that you don't get enough exercise, but you're not ready to start an exercise program, you're setting yourself up for failure; in which case a vicious cycle will ensue.
3. You'll need supportive family (parents, most likely, since you're 15 years old) and friends. They should support your new behaviors by encouraging you to keep going. Danger: Rewards in the form of chocolate cake are not supportive.
4. You'll need will power. After about 4 weeks you'll start to think, "I've been really good lately. I can slack off for a few days". Enter the aforementioned vicious cycle.
5. Change the way you eat and exercise. The two most important factors for most people to lose weight are their eating and exercise habits. If you start substituting steamed or raw veggies and fruits for chips and other snacks, that will probably take care of the diet. Also, exchange any red meat for chicken or fish and exchange sugary beverages (soda and fruit juices) for good ol' H-2-0 (water).
Finally, you'll want to get ~30 minutes of cardiovascular exercise each day. The government guidelines for exercise to maintain weight say 30 minutes of moderate intensity exercise 5 times a week. If you do this every day for the next 5-6 months, you'll shape up very nicely. That means simply walking at a brisk pace for 30 minutes. If you can stand it, jogging for 20 minute is better. But you'll want to vary this a little bit so you don't get bored with your routine. Combine biking, walking, jogging, jumping rope, elliptical machines, and anything else you enjoy doing that gets your heart rate up and your forehead sweating.
I could go on, but this is long enough. If you can do these small changes one at a time and sustain them until May, you'll be ready to face the summer with a slimmer you...provided the current you isn't slim enough already.