My summary using English
Think of receptors as doors in your brain. And Dopamine as your brain's happy chemical, sauntering around. Gorging on yummy fatty food will close Dopamine doors in your brain. Shutting out the happy! So you will have to eat more food, to get just as happy. And in our society, more is readily available.
My summary using science-y jargon
Drug addiction and obesity are based on the same underlying neurobiological mechanisms. Overconsumption of high-calorie palatable food triggers addiction-like responses in your noggin. [ © 2010 by Christine Gary] Namely, downregulation of Dopamine receptors which means you effectively raise your brain stimulation reward threshold. Low levels of dopamine are found in both obese and druggies.
Weeee're doomed. Hah! I'm kidding. There's hope. Now that they've confirmed the similarity between food/drugs reward systems, they can target obesity treatment more effectively, by modeling obesity medication after prescriptions that treat drug addiction. And another beam of hope is that this downregulation (closing dopamine doors) is reversible.
The article states, "Notably, it is unclear whether deficits in reward processing are constitutive and precede obesity, or whether excessive consumption of palatable food can drive reward dysfunction and thereby contribute to diet-induced obesity." My guess is that it's like diabetes. You can be born with type I diabetes and have it from birth. But you can also induce type II diabetes by overloading your system. Similarly, I would think there are individuals born with a lower density of striatal D2 receptors, but that doesn't sentence them to be obese. They can learn to seek reward elsewhere (no, not drugs...don't become a druggie and then tell the cops it's so you can watch your figure).