Gastroparesis is a neuropathy of the stomach (also called stomach paralysis) that is directly related to prolonged, elevated blood glucose levels and that can be part of the overall package of "things that will improve in a major way" once those levels have been brought under better control. There are medications that can help in the meantime by stimulating motility in the gastro-intestinal (GI) tract.
This is also a complication for some people with type 1 and type 2 diabetes. Another name for this condition is delayed gastric emptying. When nerves (vagus nerve in particular) to the stomach are not working properly, the stomach and intestines don't either; movement of food is either slowed or stopped. The vagus nerve controls digestive tract movement.
Gastroparesis is one of the vicious circles, complicating blood glucose regulation. When food is delayed in passing from the stomach to the intestine (where food absorption begins), blood glucose levels rise--the post-prandial bg increase.
Since the emptying of the stomach can't be predicted, it also makes bg's difficult to predict and control, as post-prandial has no average or normal expected time with gastroparesis.
For diabetic dogs and people without gastroparesis, post-prandial rise begins about 2 hours after eating. Post-prandial rise for people and pets with gastroparesis begins whenever the stomach empties the eaten food into the intestine.
Changing meal patterns may also help; switching to 4 small meals instead of 2 large ones means less enters the stomach at one time, alleviating some of the overly full problem. 
- Gastrointestinal Motility Disorders of Dogs and Cats (Gastric Emptying) Washabau, Robert J., 2005, WSAVA
- G.I. Motility Disorders: Pathogenesis, Diagnosis, and Therapy-page 100 Washabau, Robert J., March, 2010, 110th Penn Annual Conference
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