Not if you do chest toning exercises while losing weight. You don't want to lose weight without toning up your body as you go, anyways. Doing so would only cause you to have saggy skin and stretch marks all over your body. Make sure you are toning up! Also, spend the extra money to make sure A. you have a really good supportive everyday bra and B. you have a good, supportive exercise bra. As far as exercise goes, I recommend weight training every other day and cardio on the off days.
Unfortunately, losing weight quickly will lead to saggy skin. But you're also young, which means your skin is likely to bounce back.
Try to lose slowly. This is not only healthier, but it'll also reduce the saggy skin effect.
Weight-training will definitely help. Many people think that weight-training will make them bulk up or look like body builders. This isn't true. It'll actually make you look leaner, plus help with weight loss, since sore muscles use up a lot of calories to repair themselves.
You can look up a bunch of different weight-training exercises that can be done with as little as 5 lb weights. But to make it effective, you must work to the point of muscle failure. This means you lift until you can't lift anymore, until the muscles fails. It can be a challenge, because that's usually long after it has become somewhat painful. :)
But if feels great afterwards.
Aim for compound moves, the kind that work the most muscles at once, such as squats. Leg muscles are your biggest muscles, so building those up will give you a little boost with weight loss.
Also, for cardio (and some muscle-building), walking is great. Low intensity exercises help burn fat, while high intensity help build and strengthen the heart.
Good luck and keep it up!
I like the couch to 5k program, I downloaded an app for it on my iphone and i LOVE it. I will be starting week 3 today. I also started out at 240 and am down to 200. I also have exercise tv on demand and there are countless workouts I can do. I have my favorites, but they have some biggest loser workouts on there as well as kickboxing, zumba, etc. If you have it you can try out different kinds to see what you like or don't like. And I find that since I have been exercising/toning up while I have been losing weight, I haven't really noticed any saggy skin effect, I've lost the 40 pounds since October 2010 so I think I'm going at a good healthy pace. But my stomach is pretty saggy, but I contribute that to the 2 kids I have, especially since one of them is only 9 months old. Good luck with your weight loss!