Nutrition Myths
How many calories in fiber?

SUMMARY

  • In the past, fiber was assigned 4 Cal per gram of energy, which is the same as simple carbohydrates.
  • It is estimated that there are 2 calories in fiber that is composed of 70% fermentable fiber, 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.
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Calories in fiber are often calculated incorrectly

Many layman online sources claim that fiber has no calories, while some official sources include fiber in “total carbohydrates” to calculate calories in food. The fact is that there are calories in fiber, but not as many as in digestible carbohydrates.

In order to understand why there are less calories in fiber than in digestible carbohydrates such as simple sugars, 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 / gram (1, 2)

MAIN POINTS

  • Digestible carbohydrates are completely digested and absorbed and converted to energy in the body. 

How does energy get produced by fiber?

Calories in fiber are calculated differently to digestible carbohydrates.

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 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, 4)

Only the part of the fermented 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 fiber that is fermentable.

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 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) includes all 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 in fiber used by individual countries. (5, 6, 7)

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.

MAIN POINTS

  • Fiber isn’t digested by the body, but feeds gut bacteria that produces short chain fatty acids that are then absorbed and used to produce energy.
  • It is estimated that there are 2 calories in fiber that is composed of 70% fermentable fiber.

NUTRITION FACTS VS NUTRITION MYTHS

You will find a summary of the most common nutrition myths and evidence-based nutrition facts here.

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