|The 800 product has 160 calories per serving and the 500 has 100 calories per serving. So you would save about 240 calories per day by switching. In one weeks time that would be a calorie savings of 1,680 or 1/2 pound.
Keep in mind that for some people the 800 keeps them fuller longer because it does have more calories and is richer.
As long as you are eating entrees with it, and hopefully some fruits and veggies, you should be fine with either product.
I hope all is going well with your weight loss efforts. Best of luck!