Make something salty, and sweet, and starchy, and fatty, then add in some extra flavors and scents, appealing colors and a pleasing mouthfeel for good measure, and you have something that’s been scientifically engineered for us to over-eat. We naturally love and seek out these things. Evolution has equipped us for it. If you love so-called “junk food”, and feel like you can’t stop eating it, you’re not alone, bad, or weird. Your brain is doing its job to keep you alive. For example, high-fat foods are energy dense. Good news if you’re a hunter-gatherer and nutrients are scarce. A sweet taste can tell us food is safe to eat. Bitter-tasting foods could be poisonous.

Yet our ancestors weren’t exactly dialing in for delivery. They had to bust their butts with daily activity such as stalking, gathering, and digging, even for minor rewards like a meal of turtle and tubers. Today, of course, high-fat foods aren’t nutrient-rich animal organs or blubber that we had to work nine hours to get; they’re Frappucinos and bacon double cheeseburgers that we bought while seated in our car.  This is your brain on processed food.
Our brains love processed foods. But our bodies don’t. These enchanting and semi-addictive foods aren’t usually very nutritious. They have more energy than we need, with fewer nutrients (i.e. vitamins, minerals, phytonutrients, essential fatty acids, etc.) and fiber.