Is it OK to feed RES turtles.....?

whipped cream? I got curious and put a bit in some water for them and they devoured it! I was surprised they liked it so much. I know this one time won't really do any harm, but since they liked it so much, I was wondering if it is OK to treat my Red-Eared Sliders every once in a while with some whipped cream? If it helps any, it's fat free...haha! They're such good little turtles , I just want them to be happy!