Origins and Purpose of the 1918 Equation
Developed by scientists James Arthur Harris and Francis Gano Benedict, the original equations were the result of extensive research published in 1919. Their work aimed to provide a reliable method for calculating a person's basal metabolic rate (BMR), the amount of energy expended while at rest. This was a significant advancement in nutrition science, moving towards a more data-driven approach based on measurements of subjects' energy expenditure over a decade.
The Original Formulas of 1918
The 1918 Harris-Benedict equations established separate formulas for men and women to account for physiological differences. Using kilograms for weight, centimeters for height, and years for age, the formulas are:
- For Men: BMR = 66.4730 + (13.7516 × weight in kg) + (5.0033 × height in cm) − (6.7550 × age in years)
- For Women: BMR = 655.0955 + (9.5634 × weight in kg) + (1.8496 × height in cm) − (4.6756 × age in years)
Applying the Original Equation Today
While foundational, the original equations may overestimate BMR for contemporary populations due to differences in lifestyle and body composition compared to the early 20th century. For a rough estimate, the formulas are still functional. The calculated BMR is often multiplied by an activity factor to determine total daily energy expenditure (TDEE).
Limitations of the Original Formulas
As a historical tool, the 1918 equations have several limitations:
- Population Data: Based on a population different from today's.
- Body Composition: Doesn't account for differences between lean mass and fat mass.
- Activity Levels: Broad activity categories may not fully reflect modern lifestyles.
- Accuracy: Subsequent research found revised equations and indirect calorimetry to be more accurate.
Comparison: 1918 vs. Revised Harris-Benedict (1984)
| Feature | Original Harris-Benedict (1918) | Revised Harris-Benedict (1984) | Mifflin-St Jeor (1990) |
|---|---|---|---|
| Developed By | Harris and Benedict | Roza and Shizgal | Mifflin, St Jeor, et al. |
| Study Population | 239 subjects (16-63 years) | 337 subjects (wider age range) | 498 subjects (19-78 years) |
| Accuracy | Tends to overestimate BMR in modern populations | Improved accuracy over original, but less accurate than Mifflin-St Jeor | Considered more accurate for modern lifestyles |
| Key Equation Differentiator | First major formula, foundational | Updated coefficients for a larger, older population | Re-derived coefficients for a wider age and weight range |
The Lasting Legacy of the 1918 Equation
Despite limitations and newer alternatives, the original Harris-Benedict equation is a crucial part of nutritional history. It was one of the first successful attempts to quantify human energy metabolism with a practical formula. Its significance today is more historical than clinical, demonstrating the evolution of metabolic science. Its legacy is the establishment of a standardized method for energy estimation, paving the way for future predictive metabolic equations and advancements in nutritional therapy and weight management. You can read more about the evolution of the equation here.
Conclusion
The Harris-Benedict equation for 1918 is a historical formula for calculating basal metabolic rate (BMR). While foundational to nutrition science, it is largely superseded by more modern and accurate equations like Mifflin-St Jeor due to changes in population characteristics. The 1918 version reflects early scientific efforts to quantify human energy expenditure and remains a landmark in research, offering insight into the evolution of dietary science and weight management strategies.
