Basal Metabolic Rate (Harris-Benedict, Men)

James Harris and Francis Benedict measured basal metabolism in 239 subjects at the Carnegie Institution and published the original equations in 1919, which makes this the oldest widely used predictive equation in nutrition. The version here is the 1984 revision by Roza and Shizgal, refit to the original data with corrected statistics: $88.362 + 13.397m + 4.799h - 5.677a$, with mass in kilograms, height in centimetres and age in years. An 80 kg man of 180 cm aged 30 gets 1854 kcal/day.

Compare that with the 1780 kcal/day the Mifflin-St Jeor page gives for the same man, and you have the reason Mifflin exists. Harris-Benedict runs about 5 percent high on average and considerably higher in obesity, because the 1919 subjects were leaner than the population using the equation today and the mass coefficient carries that assumption forward. In people with severe obesity the overestimate can reach 10 to 15 percent, which is why most current clinical nutrition guidance prefers Mifflin-St Jeor.

Harris-Benedict survives partly through inertia and partly because an enormous amount of published work uses it, so comparing a new figure against the old literature means computing it the old way. If you are picking one for practical use, Mifflin is the better bet; if you are reading a paper from the 1990s, this is the one it used. Either way the output is a resting rate, not a daily requirement, and both equations carry the same blindness to body composition.