This is very true, scientifically proven, and it is the basis for the so-called "Okinawa diet". Human digestive system isn't very good at detecting the amount of calories in the food, so it relies substantially on quantity measures. Veggies have low energy density, and, if you eat a lot of them, your body is fooled into thinking that it's full. Chips and cookies are a lot more energy-dense (up to 20 times more calories per ounce) and they put you at risk of overeating.

There was a study where people were fed seemingly identical meals and left free to choose how much they ate, but some of them got low-calorie meals and others had their meals covertly "padded" with generous amounts of oil. Oil has 9 calories/gram and you don't need much of it to skew the energy density. Sure enough, all subjects ended up eating identical quantities of food, and subjects with largest quantities of fat in the diet averaged 1000 more calories/day than those on the basic low-fat diet.