What Causes Grey Discoloration On The Skin After Eating Sweets?

My daughter { foster} craves sweet foods constantly she can eat anything sweet from she walks in the morning until she goes to sleep, if she eats too much sweets her skin goes grey like she looks tired and her moods are terrible. when she is supported to eat healthy foods her skin and mood become a lot better, then after dinner I give her a packet of wine gums about 30 minutes to 45 minutes later her moods become terrible again . I heard it could be a lake of iron is this correct