The way we look at food has changed drastically, primarily because more and more people are looking to get fit, drop a few pounds, and attempt to improve their health. Because of this food is looked at as either protein, carbs, or fat, which is then further classified into good or bad.
Certain food groups, often times carbs but sometimes fats, are demonized in regards to diets specifically aimed at fat loss. No specific group of foods produce weightloss and no specific group of foods produce weight gain. It is all dependent upon the amount of calories consumed versus the amount of calories expended for that day, week, month, etc. It is possible for an individual to lose weight eating only donuts. It is also possible for an individual to gain weight eating only plain chicken.
I believe food should be looked at in two lights. One observing the macronutrients of the food (protein, carbs, and fats) and the other observing the micronutrients of the food (vitamins, minerals, fatty acids, etc). Having your macronutrients portioned out in a balanced manner while also adhering to the caloric load for your metabolism and goal will ensure you are progressing towards that goal and maintaining a healthy body composition.
To go along with that, comprising most of your meals with foods that are dense in micronutrients will ensure that you are also healthy and able to perform at your best. A chicken and rice diet may help you achieve your fitness goals but you will be severely deficient in many essential nutrients which will wreak havoc on your body and mind.
The best diet is a balanced diet consisting of nutrient dense protein sources, carb sources, and fat sources portioned out specifically for you and your specific goals. This way if your calories are set for the day and the bulk of your day has consisted of nutritious food and you choose to have a treat, as long as you can fit it within your macros and total calories for the day you will still be progressing towards your goal while feeling better than ever.