Metabolizable energy in humans in two diets containing different sources of dietary fiber. Calculations and analysis.
Level 3 - non-randomized controlled study
Controlled human metabolic balance study without reported randomization
PubMed 3031253 · doi:10.1093/jn/117.2.267
What was done
Metabolizable energy (ME) from two high-fiber diets (33 to 74 g dietary fiber per day) was calculated using three methods: Atwater general factors (4, 9, and 4 kcal/g for protein, fat, and carbohydrate), Merrill and Watt specific factors, and the British approach (monosaccharide equivalent multiplied by 3.75 kcal/g). These calculations were compared against measured ME from two balance experiments in 20 human subjects consuming Diet A (fiber primarily from cereals) or Diet B (fiber primarily from beans, vegetables, and fruits).
What was found
ME calculated using Merrill and Watt's specific factors agreed more closely with ME measured in balance experiments than calculations using Atwater factors or the British approach. Dietary fiber in Diet A contributed 2.5 ± 1.4 kcal/g to ME, while dietary fiber in Diet B contributed 3.1 ± 1.2 kcal/g.
Why it matters
This study shows that dietary fiber is not non-caloric and provides roughly 2.5 to 3.1 kcal/g of metabolizable energy depending on its food source, supporting the use of specific rather than general Atwater factors for high-fiber diets.
Limits
The sample size was small (n = 20). The abstract does not report participant demographics, baseline characteristics, study duration, or whether diet assignments were randomized.
Cited by
- supports Wilbur Atwater established the caloric conversion values of approximately 4.1 calories per gram of carbohydrate and protein and 9 calories per gram of fat.