The sf jello may be sweetened with aspartame. Aspartame causes stalls in some people, that is why aspartame is not encouraged on Atkins. What you could do instead of aspartame-sweetened jello is to either purchase readymade jello that has been sweetened w/Splenda (brand is Jolly Rancher) or to make your own Splenda Jello (following Skamito's/Angela's recipe):

2 packets of Knox unflavored gelatin
1 packet of Kool-Aid flavoring (unsweetened)
8-10 packets (16-20 teaspoons granulated) Splenda to taste
1 cup hot water
1 cup cold water

You can use a variety of flavors because of the amount of Kool-Aid flavors. Happy LCing!