The glycemic index (GI) is a ranking system for carbohydrates based on their effect on blood glucose levels. The higher the GI, the faster and bigger the corresponding insulin spike and thus potential weight gain.
Granular Splenda has 24 carbs per cup. I know that the label says "less than 1 g" but that is assuming a 1 teaspoon serving size. Sucralose is what makes Splenda sweet and it has virtually no carbs. The carbs from Splenda come from a filler called maltodextrin. This is used to give Splenda equal measure to sugar. The danger is that maltodextrin has an extremely high glycemic index of 105. This is 5 points higher than glucose which is 100. And, it is almost double that of table sugar which is around 59.
Don't get me wrong. Sugar has more than 8 times the carbohydrates of granulated Splenda. So, you are still better off eating granular Splenda. But carb-for-carb sugar is perhaps less unhealthy.
Splenda Quick Packs however are a special type of Splenda designed to quickly dissolve in liquids. Typically it is available in the KoolAide section of grocery stores. Splenda Quick Packs have less maltodextrin and only 4 net carbs per pack which is the equiv. to one cup of sugar. Therefore, if you are making a dessert that calls for one cup equiv. of sugar, using a quick pack instead of granular splenda spares you 20 carbs that would have had a high GI.
An even better alternative is Sweetzfree. Sweetzfree is a highly concentrated solution of sucralose in water. It has no filler other than the water and therefore has no measurable carbohydrates and no glycemic impact. This is what I use most often in my own kitchen. The price sounds high, $18.00 for a one ounce bottle. But keep in mind that this is the equivelent to 24 cups of sugar. It comes in a little dropper bottle. One drop equals a teaspoon of sugar. 1/4 teaspoon equals an entire cup of sugar. My wife sometimes keeps a small bottle of this in her purse. A single drop instantly turns tea into sweet tea. The downside is that Sweetzfree is only available online and due to limited supplies is only sold on certain days of the month. I'd love to see this product available in stores.
I wonder how long it will be before Splenda wisens up and sells concentrated sucralose? It seems that they are taking the other direction, combining granular splenda with regular forms of sugar marketed toward good tasting baked goods rather than the lowest carb diet baked goods. I would suspect that if they'd sell little dropper bottles that there'd be one heck of a market.