Nutrisystem's doctors and dietitians have designed the program's meal plan in such a way that you get the most nutrients for the lowest possible amount of calories. Without knowing the number of calories your body burns, there is no way you can know how much food you are allowed to eat each day in order to reach your weight loss goal. Consuming the right amount of calories is one part of a successful weight loss regime. Losing weight is first and foremost an issue of eating the right amount of calories energy. This doesn't mean that you get to eat nuts, oatmeal and dry chicken. This is why before starting a weight loss program, doctors and dietitians will always calculate your metabolic rate--the energy you expend throughout the day.
All brands will contain some amount of the extract from the actual fruit, but the amount of the active substance can vary a lot. There are plenty of fly-by-night products around(pretty much all of the ones in local stores) that only offer a very subpar purity.
Often times such supplements(like ones sold at WalMart) only contain 20 or less HCA- even when they are marked as higher(this was the conclusion of a recent study). Such low-grade products(like the ones from GNC usually) are basically scams, replete with fillers and additives and dont do much to give you the true benefits of the natural extract.