calories in fiber

How many calories are in fiber?

Pawel Malczewski
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Short summary

In the past, dietary fiber was assigned 4 Cal per gram of energy, which is the same as simple carbohydrates.

However, in the last 10 years, scientists throughout the world have shown that a more accurate measure for dietary fiber is 2 Cal per gram of energy, which has been adopted by most countries as a standard.

Despite strong evidence, the U.S remains one of the few countries that still assigns the previous measure.

Manufacturers are allowed to exclude insoluble fiber from the calorie calculations, but most sources continue to use 4 Cal.

Explanation

In order to understand why dietary fiber cannot be treated the same as simple carbohydrates in energy calculations, it is important to understand how they both produce energy.

How do carbohydrates generate energy?

Carbohydrates from food get broken down into smaller units. Its digestion starts in the mouth, continues in the stomach and is completed in the small intestine, where the majority of the breakdown occurs. In the small intestine, carbohydrates break down completely to form the simplest carbohydrate units (glucose, fructose and galactose), which are then absorbed by the blood. Absorbed glucose is ready to provide energy, while fructose and galactose are first converted to glucose in the liver.

The approximate energy that carbohydrates provide is 4 Cal per gram. (1)Wolever TM, Jenkins DA. Effect of Dietary Fiber and Foods on Carbohydrate Metabolism. In: Spiller GA, ed. CRC Handbook of Dietary Fiber in Human Nutrition. 3rd ed. Boca Raton: CRC Press; 2001:321-360. Available here. (2)Your Digestive System and How It Works. NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. Available here.

How does energy get produced by dietary fiber?

Dietary fiber is a type of carbohydrate that isn’t digested by the body. Instead it passes through the entire digestive system and is excreted from your body relatively unchanged.

However, there is one type of dietary fiber (called fermentable fiber) that is fermented by “good” bacteria living in the colon. The product of this fermentation is short-chain fatty acids and gases. Short chain fatty acids are then absorbed and used to produce energy. It is estimated that on average 70% of fiber in foods are fermentable, but this may vary since some foods may have different ratios. (3)Your Digestive System and How It Works. NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. Available here. (4)Slavin J. Fiber and Prebiotics: Mechanisms and Health Benefits. Nutrients. 2013 Apr; 5(4): 1417–1435. Available here.

Only the part of the fermented dietary fiber that results in the production of energy can be used to calculate calories. Non-fermentable fiber (the majority of insoluble fiber) provides 0 Cal of energy.

The most accurate and up to date average estimate is 2 Cal (8kJ) per gram of fiber, assuming that fibrous foods contain on average of 70% of fermentable fiber. This amount has been adopted by most countries in the last 10 years. (See the table below)

The U.S remains one of the few remaining countries that still assigns 4 kcal per gram of dietary fiber. Please note, however, that manufacturers are allowed to subtract insoluble fiber from calorie calculations since insoluble fiber is mostly non-fermentable. The majority of the online data though (including USDA) (5)Agricultural Research Service. United States Department of Agriculture National Nutrient Database for Standard Reference Release 27. Available here. includes all dietary fiber in the calculations of calories which is incorrect and misleading. Please also note that most nutritional websites use the USDA database for calorie calculations.

Here is a table showing amount of calories assigned to fiber by individual countries. (6)Nutrition Evaluation Division Bureau of Nutritional Sciences Food Directorate Health Canada. Proposed Policy: Definition and Energy Value for Dietary Fibre. Available here. (7)Nutrition Evaluation Division Bureau of Nutritional Sciences Food Directorate Health Canada. February 2012. Policy for Labelling and Advertising of Dietary Fibre-Containing Food Products. Available here. (8)Food Standards Australia New Zealand. Calculation of values for nutrition information panel. DRAFT: 21 February 2014. Available here.

Country / organizationCal/g of fiberSpecial notes
USA4 kcal (17 kJ)Dietary fiber is included in total carbohydrates and therefore in the calculations of calories, but manufacturers can subtract insoluble fiber.
Australia, NZ2 kcal (8 kJ)
Japan2 kcal (8 kJ)
Nordic countries2 kcal (8 kJ)
European Union2 kcal (8 kJ)
Canada2 kcal (8 kJ)Currently in the process of adopting the change to 2 Cal per gram of dietary fiber.
FAO/WHO 2002 Recommendations2 kcal (8kJ)Assumed that 70% of fiber in foods on average is fermentable.

Click here to see the list of the healthiest high fiber foods.

References   [ + ]

1. Wolever TM, Jenkins DA. Effect of Dietary Fiber and Foods on Carbohydrate Metabolism. In: Spiller GA, ed. CRC Handbook of Dietary Fiber in Human Nutrition. 3rd ed. Boca Raton: CRC Press; 2001:321-360. Available here.
2. Your Digestive System and How It Works. NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. Available here.
3. Your Digestive System and How It Works. NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. Available here.
4. Slavin J. Fiber and Prebiotics: Mechanisms and Health Benefits. Nutrients. 2013 Apr; 5(4): 1417–1435. Available here.
5. Agricultural Research Service. United States Department of Agriculture National Nutrient Database for Standard Reference Release 27. Available here.
6. Nutrition Evaluation Division Bureau of Nutritional Sciences Food Directorate Health Canada. Proposed Policy: Definition and Energy Value for Dietary Fibre. Available here.
7. Nutrition Evaluation Division Bureau of Nutritional Sciences Food Directorate Health Canada. February 2012. Policy for Labelling and Advertising of Dietary Fibre-Containing Food Products. Available here.
8. Food Standards Australia New Zealand. Calculation of values for nutrition information panel. DRAFT: 21 February 2014. Available here.

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