Drinking sports drinks while playing live

[Frond]

This morning I went to my chiropractor(who I haven't seen in a while)for a treatment on my back and neck. I just happened to mention to him that I play live poker about 3 times a week for about 3-5 hours at a stretch. He started to tell me about how he had read somewhere that when chess players play for like 3 hours at a time that they actually burn way more calories than one would think from the intense concentration and focus etc. He recommended to me that I drink plenty of sports drinks in addition to obvious high amounts of water for hydration. But particularly the sports type drinks. I know that after a live session I to fell fatigued at times but had no idea that I may be burning as many calories as I thought I was merely from intesnse mental concentration. I eat and drink plenty of water when I play. Anyone have any info on this possible caloric burning at all? I guess it is possible but not sure.