A gene, also present in humans, makes those Labs insatiably hungry. No matter how much or how recently they’ve eaten, they always want more.
I used to think all dogs were that way until we got Minnie. We free-feed her. She eats just enough to maintain her weight, and leaves some uneaten food in her bowl. We put out food for her twice a day, and she almost always skips the morning meal.
This Is Why So Many Labrador Retrievers Are So Very Fat – Melissa Dahl, The New Yorker