Because food scientists have engineered them to be that way. Here's is an excerpt about Doritos, a food that is widely considered among food scientists to be perfect, in an awful way. As you read this I encourage you to think about McNuggets, and all the similarities they share. >They’ve been engineered so you never feel like you’ve had enough. Here’s why: >The chips have the powerful savory flavor known as umami, and also what Mr. Witherly calls “long hang-time flavors” like garlic that create a lingering smell that stimulates memories. >The recipe balances these powerful tastes so well that no single flavor overpowers and lingers in the mind after you’ve eaten a chip. This avoids what scientists call “sensory specific satiety” or the feeling of fullness caused by a dominant flavor. >You wouldn’t eat a whole bag of rosemary chips, would you? But you keep coming back for more and more nacho cheese Doritos. >Two acids – lactic and citric, get the saliva flowing – which triggers the impulse to eat. Another ingredient, buttermilk, delivers even more lactic acid. >Dorito dust has even more impact if you lick it right from your fingertips without the chip to dilute it. >To maximize the pleasure, half of the calories in Doritos come from fat. With that ratio, it feels like the chip melts on your mouth and your brain is tricked into thinking the calories have vanished too. This is called “vanishing caloric density” and it comes with cotton candy too, for example. >To boot, there’s the three artificial colorings which research shows consumers are attracted to. >And the blend of ingredients is ground so finely (one of the finest grinds in food processing in fact) that the powder fills every nook and cranny of your mouth. This type of palate manipulation is now used in many, many different highly processed foods. Stay away from Doritos.