There is a link between digestion and metabolism, but then every system is interlinked. It is possible to have a slow digestion and a normal metabolism, for example if your digestive system lacks a particular enzyme, has slow peristalsis, etc.
Here's a link to several articles that discuss various aspects of your question:
[url="http://www.nlm.nih.gov/medlineplus/foodnutritionandmetabolism.html"]http://www.nlm.nih.gov/medlineplus/foodnutritionandmetabolism.html[/url]
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question about digestion... 
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