Energy requirements: the case for the factorial model

Area of Science:

• Human physiology
• Nutritional science
• Metabolic research

Background:

• Previous methodologies for human energy requirements (ERs) are questioned by the Food and Agriculture Organization and International Atomic Energy Agency (IAEA).
• IAEA proposes predictive equations using doubly labeled water (DLW) data to estimate population ERs, deeming the factorial approach unnecessary.
• Concerns exist that predictive equations may not adequately account for physical activity energy expenditure (PAEE) variations.

Purpose of the Study:

• To re-examine the factorial model for human energy expenditure and requirements.
• To investigate whether total energy expenditure (TEE) is constrained within a narrow physiological range, irrespective of physical activity.
• To analyze interindividual variation in PAEE within different population groups.

Main Methods:

• Re-examination of the factorial model for energy expenditure.
• Derivation of weight-adjusted metrics for physical activity energy expenditure (PAEE).
• Analysis of published energy expenditure data from traditional populations and comparison with a DLW dataset for UK dietary reference values.

Main Results:

• Analysis revealed very high rates of energy expenditure in traditional populations.
• These findings suggest lifestyles with no obvious evidence of energy constraint.
• The results challenge the notion that TEE is a constrained product of physiology and does not increase with physical activity.

Conclusions:

• Any update to human energy requirements must account for interindividual variation in PAEE.
• The factorial model, when properly accounting for PAEE, provides valuable insights into energy expenditure.
• The assumption of a constrained TEE may be inaccurate, particularly for diverse populations with varying activity levels.