Unexplained weight loss

Question
My lab/spaniel mix has been losing fat and muscle.  Her stool sample was negative, and so were blood tests and urinalysis.  Except for the weight loss, and being extremely hungry all the time, she doesn't have any other symptoms.  She seems happy and alert, normal stool, no vomiting.  Her vet will be taking x-rays and doing a cleansing enema next.  Is there anything else I should ask him to look at?  His best guess at this point is a digestive maladsorption problem or cancer.  
Her normal weight hovers around 50 pounds.  She is now down to 39 pounds.  She is an 8-yr-old spayed female.  Her only health problem in the past has been mild hip dysplasia, but it doesn't bother her unless she gets overweight.

Thanks.

Answer
I would check a TLI to see if there is pancreatic insufficiency as well as a B12 and Folate level to check for maldigestion and bacterial overgrowth.

I would recommend a high quality diet that is all-natural and free of dyes, preservatives, by-products such as those made by Prairie (I feed my cats this and they love it--very high quality food), Flint River Ranch, Nutro Natural (our beagles eat this), Innova, Eagle Pack, Natural Balance, Precise...

I would also add digestive enzymes to her diet such as Dancing Paws Shake 'N'Zyme (I add this to my cat's food since one of them has inflam. bowel disease), Prozyme or Viokase.

There is also a recipe for SATIN BALLS which can be used for weight gain and you could supplement her diet with these as well.

INGREDIENTS:
10 pounds of hamburger meat

1 large box of Total cereal

1 large box of oatmeal (uncooked)

1 jar of wheat germ

10 eggs

1-1/4 c. vegetable oil

1-1/4 c. unflavoured molasses

10 small packages of unflavored gelatin

pinch of salt

DIRECTIONS:

Mix all ingredients together well, much like a meatloaf

Put into separate freezer bags and freeze, thawing out as needed.

Make little meatballs and place them on top of the food  

It puts weight on in a very short time not to mention adding gloss the coat.  Use it every day when showing -- does not  produce diarrhea.  It can be fed alone or, to save money, with their regular food.  If you are unable to obtain all the ingredients (i.e.-the molasses and the unflavoured gelatin), it will still work wonders on your dog.