Dieters that count Calories may be interested to know that they may be able to subtract fiber Calories from the total Calories in the foods they eat. Fiber is a form of complex carbohydrate that is generally not absorbed nor digested as it passes through the human digestive system. If the nutrient isn't absorbed by the body, then the theory goes: it doesn't have to be included when adding up one's daily Calories! This is often welcome news to the Calorie counter who is trying to lose weight. However, not all types of fiber pass through the digestive system unchanged, therefore some fiber Calories do count. Still, foods rich in fiber are often seen as an important source of Calories among dieters because they satisfy hunger more with fewer Calories.

There are two types of dietary fiber — soluble and insoluble — and for the purposes of counting Calories, it is necessary to distinguish between the two. Soluable fiber refers to the type of fiber that disperses in water, whereas insoluable fiber refers to the type that doesn't. When soluble fiber disperses in water it generally develops into a gel-like substances which slows down digestion. This type of fiber is generally considered to contribute to Caloric intake. Insoluble fiber, on the other hand, doesn't dissolve in water, and because it passes through the body without much change, it's generally not considered to contribute to Caloric intake.

How much energy is in fiber, and therefore how many Calories are in fiber, is still unclear. According to a 2002 report by the Institute of Medicine (IOM) regarding dietary reference intakes, the energy yield of fiber when consumed by humans is somewhere in the range of 1.5 to 2.5 Calories (kCal) per gram (6.3 to 10.5 kilojoules per gram).

Whether fiber Calories are included in food nutrition labels varies among countries. Some countries do not include fiber Calories. In the US, the Food and Drug Administration (FDA) does not require manufacturers to include insoluble fiber in fiber Calorie counts on nutrition labels, usually as a subset of the total carbohydrate count. According to the United States Department of Agriculture (USDA), the general practice within the food industry is not to include insoluble fiber in the total carbohydrate count.

When fiber is listed as a part of a food's total carbohydrate content, it is counted at 4 Calories per gram — just like all other carbs. The reason fiber Calories are counted is because when fiber is processed, the bacteria in the large intestines ferment the fiber, producing chemicals that get absorbed by the body. So, indirectly, fiber contributes Calories.

Some dietitians argue that since the body doesn’t burn fiber, fiber Calories can be subtracted. So, take for example a breakfast cereal that has 130 Calories and 9 grams of fiber per serving. If a Calorie counter is subtracting his or her fiber Calories, she'll be able to mark that meal as 94, instead of 130, Calories. That's because each gram of fiber is estimated to have 4 Calories.

The IOM reports the median daily intakes of fiber to be 16.5 to 17.9 grams per day for men and 12.1 to 13.8 grams per day for women. The FDA 2005 Dietary Guidelines recommends 14 grams of fiber per 1000 calories consumed. US food nutrition labels note the amount fiber in a food as compared to the recommended daily intake. This percent is based on a 25 gram daily intake. Generally, dietitians recommend between 25 to 35 grams of fiber a day but the proper amount can vary among people based on weight, activity levels, and other health considerations. Trainers and nutritionists say people that are counting their Calories in order to lose weight should eat a good amount of fiber.

The best way to obtain dietary fiber is to eat foods such as fresh fruit, vegetables, beans, and whole grains, like oat bran. The benefits go far beyond simply ingesting semi-empty Calories that make one feel full. Fiber helps treat and prevent constipation, hemorrhoids and diverticulosis, and helps decrease blood cholesterol levels.