NEW YORK (AP) ? Chips, soda and frozen pizzas tend to be full of salt, sugar and fat, but now scientists are trying to understand if there's something else about such processed foods that might be bad for us. Already, the spread of cheap, packaged foods has been linked to rising obesity rates around the world. Yet advice to limit processed foods can seem unhelpful, given how convenient they are and the growing array of products that fall into the category. While three recent studies offer more clues on how our increasingly industrialized food supply may be affecting our health, they also underscore how difficult nutrition science and advice can be. Here's what they say.