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In “Are we meat eaters or vegetarians? Part II” (21. September 2009, 22:32 Uhr), Dr. Michael Eades says:

In April 1995 an article appeared in the journal Current Anthropology that was an intellectual tour de force and, in my view, an example of a perfect theoretical paper.  “The  Expensive-Tissue Hypothesis” (ETH) by Leslie Aiello and Peter Wheeler demonstrated by a brilliant thought experiment that our species didn’t evolve to eat meat but evolved because it ate meat.

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In keeping with a great scientific tradition, Aiello and Wheeler were able to see what they saw because they stood on the shoulders of giants who came before them.  In their case the giant was Max Kleiber, an animal physiologist working at the University of California at Davis, who published a groundbreaking paper in 1947 and a scholarly text titled The Fire of Life in 1961.  Kleiber’s work involved the meticulous measurement of the metabolic rates of numerous animals, including humans.  As he plotted the various metabolic rates, he discovered an extremely strong correlation between the mass of an animal and its metabolic rate.  Kleiber found that this relationship held constant across numerous species.  His October 1947 paper in Physiological Reviews simply titled “Body Size and Metabolic Rate” was a classic.  By using the equations Kleiber worked out, the metabolic rate of virtually any animal could be determined simply by knowing the animal’s body size.

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Since all animals measured have conformed to Kleiber’s law, Aiello and Wheeler postulated that animals now extinct – including our human and pre-human predecessors – would have fallen along the same line. Using skeletal remains paleontologists have been able to calculate body sizes of extinct animals along with pre-Homo and early-Homo species.  Then using Kleiber’s law, it is possible to closely estimate the metabolic rates of these creatures.  And here’s where it gets interesting.

According to Kleiber’s law, an australopithecine weighing 80 pounds would have the same metabolic rate as a human weighing 80 pounds despite the disparity in brain size between the two.  The much larger brain of the human would have 4-5 times the metabolic rate of the brain of the australopithecine, yet would have the same overall metabolic rate.  What gives?

The Blog of Michael R. Eades, M.D. © mreades 2009

Read Dr. Eades’ article to find out the answer! And more! It is a fascinating article.

Some of the development and hierarchy of science is made clear in it. But to see where it all came from, we’d have to trace this back to the work to study human metabolism in the first place, to Joule’s work in the mechanical equivalent of heat, to Mayer’s work in the conservation of energy principle, to Harvey applying mathematics to biology. And to the development of the math that made the knowledge possible in the first place.

In a comment to Dr. Michael Eades’ post “Are we meat eaters or vegetarians? Part II” (21. September 2009, 22:32), Gabe says (at 22. September 2009, 20:26):

Thanks for the comments Mike. You know I had to try to check some numbers myself… though not very thoroughly tonight. I did find, however, a couple of references that suggest that muscle metabolic rate is indeed ‘not all that’, and it may be overestimated in most cases. In one reference (Am J Clin Nutr 2006;84:475–82) [http://www.ajcn.org/cgi/reprint/84/3/475], Robert Wolfe suggest that “every 10-kilogram difference in lean mass translates to a difference in energy expenditure of 100 calories per day, assuming a constant rate of protein turnover.” That’s only about 10 cal/kg muscle (or ~5 cal per pound of muscle!). The other reference, a bit older (Obes Res. 2001;9:331-336) [http://www.nature.com/oby/journal/v9/n5/pdf/oby200142a.pdf], the authors propose a classification scheme founded on body composition level (whole-body, tissue-organ, cellular, and molecular) and related components as the resting energy expenditure predictor variables. Rather technical but if some of the equations are applied to muscle, then we find that muscle the daily metabolic rate for muscle is just about 6 calories per pound per day, not very far from Wolfe’s predictions and very low indeed!

I can see how this could lead to the notion of ‘exercising is a waste of time’. While the increase in metabolic rate is modest at best (or right out low…), at least is higher than the metabolic rate of a similar weight of fat, which is about 2 calories per pound per day. Perhaps the lesson is that the right kind of exercise (resistance in this case, and probably more on the heavier side of weight training) improves body composition by burning more calories than fat in the hours after exercise and by preserving lean body mass while dieting for weight loss. In any case, certainly there may not be such thing as three extra pounds of lean muscle burns about 10,000 extra calories a month as I seem to remember from “Power of 10: The Once-a-Week Slow Motion Fitness Revolution”.

The Blog of Michael R. Eades, M.D. © mreades 2009

As in the previous post, we could not grasp these facts without…math!! (And physics. And chemistry. And philosophy.) How ubiquitous math is, but how perplexing it is that people don’t grasp how math useful is.