Greetings,
I had the opposite problem with my ailing Yorkie in the last few months of her life. She took forever to eat her food & I had to supplement it with canned food. That's where the problem with the other two began. They stole food & ate alongside her more than I thought they did.
Samma had never been lightweight... But she didn't look fat --you could feel her ribs still. But she had really short legs, a big butt, and she hid all of the weight in her chest between her front legs.
The vet kept telling me she was ok... but after having to put Pepper to sleep, I began to notice that she just wasn't moving right. She weighed 22 pounds!!! Chienne wasn't much better at 21 pounds. Her waist wasn't as nipped in & her hip area was broad. Again, I could still feel ribs.
Samma would do the same thing that your overweight puppy does... whine & nag for food. I had to cut her down gradually... no overnight crash diets. Exercising went up, gradually too. I was concerned about her back & legs being strained.
Two hours walking at a time with a bad leg is not good for your dog. Splitting the time in the morning & evening will help. It will also inhibit the appetite, just like in humans. Even though your dog walker is "reputable" getting out with your dog will help to bond & see how he's doing physically. This will take time.
You don't say how much he weighs & what ideal weight you're aiming for. But figure that the first couple of weeks, he'll lose inches & gain muscle ---if he's been a couch potato most of the time. Slow & gradual is the best way for him to lose his weight. Once he does lose it, you have to keep him conditioned --- just like a human, he'll gain it back if you don't watch him.
Both dogs lost the weight in about 4-5 months in 1998 and have kept it off ever since. I have to watch Samma like a hawk though. Chienne remains around a normal weight of 17 pounds. Samma slightly pudges & gets soft in the winter. Walking & running when I'm just walking, just doesn't keep her in tone..but she muscles up quickly when spring hits....
They're in shape now after 2 weeks of gradual conditioning running alongside my bike. Samma's looking nice and sleek at 15 pounds. I have a picture of her at 22lbs. She looked like a long blonde haired slug. 7 pounds is a big deal for such a small dog. Yes, her skin is loose in places if I pull gently on it. When we start going long distances again (over a mile & half) I have a bike trailor that they both fit into when they get tired.
My best suggestion is when your dog starts nagging.... send him to "his" bed. Somewhere in the living/family room....not where he sleeps, but where he rests during the day. When you eat...he goes there. If he sits next to the fridge... move him to his bed. He stays there for as long as you decide. You'll have to move him there several times.. but he'll get the message that the "Kitchen is closed." If you feed him, you're only giving into his demands.
good luck,
toodles