All foods have three types of calories. Fat calories, Carbohydrate calories and Protein calories.
If a person is trying to lose weight then they should try to stay away from foods that are high in fat calories. If they are consumed in to much excess they are stored in the body.
There are some people that weight issue is to gain weight (lucky them), they should consume foods that are high in fat calories as they will stick to the ribs.
Carbohydrate calorie foods are OK as long as they are not consumed in large amount
Foods that are high in protein calories are excellent diet food as they are not stored in the body, they get used right away.
Protein calorie food are string beans, okra, fish products.
Fish products are good diet food as long as it is not breaded and no mayonnaise has been added, such as tune salad.