The Physical Rules

of Nutrition, Metabolism, and Exercise Science

Exercise Physiologist Ed Watson Teaching Exercise Science & Nutrition to All Audiences

by Professor Edward Watson

Since 1992

  • Specialized Educational Materials
  • Seminars and Private Consulting


Metabolism of Mice and Men, Birds and Elephants

Birds, mice, and other tiny mammals use much more O2 than humans do (adjusted for body weight).

This greater metabolic rate converts a greater proportion of “Total Energy Out” into “Wasted Heat” and is especially critical for surviving cold temperatures.

In order to sustain a very high rate of metabolic combustion and heat production compared to humans, birds must eat up to 17x or more the quantity of energy than a human, relatively. Despite eating so many calories, tiny animals do not gain mass because they dissipate heat extremely quickly.

This explains why a bird ‘going to bed’ on an empty stomach dies over a cold bitter night… lack of calories reduce heat production.

Conversely, the bodies of huge animals like elephants conserve heat because their size prevents rapid radiation of energy. Hence, the elephants huge ears serve as radiators to dissipate the heat.

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