For people trying to lose weight fiber can give you a satisfied feeling for a longer period of time then high sugar, high carb, low fiber food. Thus, with a high fiber diet you typically eat less. Calories from fat are the easiest to store, thus using little in the way of calories to store as fat on your body.
Calories from protein are the most difficult to convert to fat, using the most calories in the process, making them less of a calorie than calories from fat or sugar. High fiber food can make the digestive process easier, whereas high fat food does the opposite, increasing the likelihood of constipation. Sugar is so enjoyable to eat for most people that food manufacturers add it to most foods to make it taste better. Avoid foods labeled "low-fat" they are often very high in sugar.
Look for single ingredient foods. Like meat, fruits & veggies, skim milk, etc. They are low in the things you don't want, & high in the things you do want.
