If you compare gram for gram calories, it is probably about the same as other protein powders. It is easy to change the number of calories per scoop by simply changing the scoop size.
Right now, I'm using a protein that has 200 calories per 44g. scoop. It does have more calories than most, but it also has a lot more fiber than most.
the sugars probably come from the lactose as most chocolate proteins use unsweetened cocoa powder to flavor it and then some sort of artificial sweetener to sweeten it (mine uses sucralose).
If you're unacceptably low on calories, is 100 calories really going to do the trick? You could mix it with other things to fill in the gap more - 1 T. of almond butter adds another 100 calories.
100 lbs. down plus a carrot for every 5 more