Dogs don't eat, super skinny

Hi,
Currently, I'm babysitting two dogs for my friend while she's away for the weekend, which I do frequently. The dogs are brother and sister, both mutts, (one's pretty tall, a bit bigger than lab size, the other's a little smaller, I have no idea what they are, but I guess you could say that have the "body-ish look of a lab"). Anyways, ever since I've known them (the dogs are about 3-4 years old), they've been underweight, like very obviously, since you can count each one of their ribs. They constantly have dishes full of food, which they BARELY ever eat (clearly). The thing is, they readily accept table scraps, but don't readily eat dog treats. The weirdest thing about their non eating is that when I babysit them, I bring them over to my house, and I feed them my dog's food. They gobble it up, drink a ton of water, (they'll eat as much as 6 cups of food in one standing!). So, I recommended the food that I feed my dog to them, and they changed to that same stuff, but the dogs STILL don't eat when it's at their house! It's also really weird because they seem to have TONS of energy all the time, and I believe they go for runs a few times a week. My friend (who owns the dogs) has said that they've taken them to the vet and that everything's okay aparently, but I don't know, they just seem so skinny.
My question is, what might be the cause of this, and is it easily fixed? It doesn't seem to affect them much, though they can be quite skiddish...if that has anything to do with it.
PS- they have a personal trainer for the dogs, so I'd guess if there were any obvious health problems then they'd know?

Have they been checked for worms?

It may be the breed/s in them. Northern breeds like huskies will often save their food, going for long periods of time without eating, and still maintain a great deal of energy.

It sounds as if they are free-fed. Some dogs who are free-fed develop the habit of not eating because they know that food will always be there. If they are fed meals, and have the food taken away after 15 minutes, they may start realising that they only have one chance to eat so they'd better do it. Alot of dogs are also in tune to what they are allergic to and will refuse to eat a food they know they are allergic to.

I had a huge problem putting weight on Visa when I fed kibble. I tried plenty of foods, and she would eventually stop eating most of them. The ones she didn't stop eating I wasn't satisfied with because they didn't help with other things, like dandruff or bad breath. So I switched to a raw diet, and things have been spectacular since.

Try looking up the recipe for Satin Balls. :)

There's a better than even chance that if the owners panics when they do not eat dog food, and proceed to feed them table scraps, then the dogs are holding out for table scraps. In another words they have trained their owner well. Then you come along and give them the option of eating dog food or dog food. Their choice is sort of easy at that point- eat dog food or go hungry.

The fact the dogs have high energy eliminates a multitudes of possible health problems. You might suggest to the owners that they wait the dogs out. No table scraps period. The chances are after a couple days of hunger strikes the dogs would cave in, and start eating the dog food.

The dogs are smart. Table scraps are often way healthier for dogs than processed food (unless the owner eats a lot of junk food). I agree that they probably have the owner well trained. Being skinny isn't a bad thing though.

Thanks for the information.
Since they've gotten the trainer, they have stopped feeding the dogs table scraps. I'm not sure how long the dogs have been off eating table scraps, but they're still skinny. I guess it's nothing huge to worry about though, since their food is always there, and if they eat it only periodically, wouldn't that be considered grazing? If so, I guess that's only normal, since lots of dogs eat like that...

My boss's dog, Rocky is the same way. He's a golden retriever and as skinny as he can be. Yet tons of energy. I agree with what wolfsoul said:
Alot of dogs are also in tune to what they are allergic to and will refuse to eat a food they know they are allergic to. I think Rocky's got an allergy to corn. When I tell my boss this, he just laughs. Some people just think dogs are meant to eat kibble, period. But it's gotten to the point that he has to feed the dog something else b/c the dog just won't eat the kibble.
That is strange that the dogs won't eat the same food at their own house that they will eat at yours. :confused:
But as long as their energy holds up, that's the main thing. :)