Want to fight depression? A new study suggests to stay away from processed and fatty foods.  Researchers at University College London say a diet loaded with fish, fresh veggies and fruit can prevent people from getting depressed, while people who have lots of fats and processed foods on the menu could be in trouble.  Doctors say it's because fruits and vegetables are packed with protective antioxidants, and fish contains polyunsaturated fatty acids that stimulate brain activity.