Hi Weepete,
A word of caution about 'sugar-free' labelling - it can be seriously misleading. It ought really to be rephrased 'sucrose-free' because it only really relates to the amount of that particular sugar in the food. The jam, for example, still has 56g of carbohydrate per 100g, most of which will still be sugar. This is probably fructose, a fruit sugar, which raises blood glucose a little more slowly, but just as much as sucrose for many people. Look at the labelling for any ingredient ending in -ose or -ol, all of which are sugars.
As for the low-carb diets out there, there are quite a few. The very first diet book ever published was written by William Banting in 1862 and entitled 'Letters on Corpulence'. Catchy, eh? These days there are a few more to chose from, such as Protein Power, South Beach, Atkins and Richard Bernstein. They all work on much the same principle, that insulin is the key to weight gain, and weight loss is a consequence of lower insulin levels - hence low carbohydrate diets are the most effective and nutritionally complete.
All the best,
fergus