They're not too many calories each, and I definitely burn off more than I take in at the rate I take them, but they're a good quick hit of sugar. Dextrose gets into your bloodstream very quickly, so it's fast acting.
I've only got half a packet in my bag - they're 364 calories per 100g, 91g of carbs of which 81g is dextrose (out of 82g of sugar). The ones I have also have vitamin C, but that doesn't help my energy on the run. I don't know how much each tablet weighs, I've not got the half of the pack that has the weight on so I can work it out... But I can't see the packet being much more than 50g (if that), and I rarely get through a full packet, even on a 20 miler, so calorifically it's not a big problem. I only use them if I'm running more than about 13.
SW - 260, Original GW - 160 - achieved 21 March 2006, CW erm... I'll get back to you on that
4 sub-4 hour marathons! (PB 3:44:05)!