Well as he is an outdoor boy he might be carrying a parasite load from the wildlife he eats or from fleas he may have picked up and groomed off himself.
He might also have an infection of some sort, or be diabetic, or have a thyroid issue.
Toxoplasmosis, feline infectious peritonitis and other diseases all can present with weight loss and shedding due to nutritional changes as one of the symptoms.
Your best bet is to bring him into the vet as the symptoms you list are ones that could be indicators of a serious problem - catch is which serious problem it is is hard to determine over the net!
Hope this helps!
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