Environmental Engineering Reference
In-Depth Information
5
H
UMAN
E
NERGETICS
People as Simple Heterotrophs
Nutritional individuality is a characteristic of mankind,
and this is as true of energy intakes and needs as of other
attributes. Studies over the years have shown that individu-
als vary by a factor of two or more in their intakes of energy
from the first year after birth to 75 years and over. The
metabolic differences that must lie behind this are still not
fully understood.
Elsie Widdowson, ''How Much Food Does Man Re-
quire?'' (1983)
movers, a shift that has been largely responsible for
removing human energetics from the core of energy
studies and its relegation to specialized niches of physio-
logical and nutritional interest. This reality has not
changed the fact that no energy conversion is more im-
mediately essential for human existence than the con-
tinuing oxidation of foodstuffs or lipid reserves (and if
need be, protein reserves).
Specialized studies of human energetics have advanced
in many fascinating ways, ranging from the minutiae of
cellular biochemistry to appraisals of the biophysical lim-
its of the human body as a machine. But many funda-
mentals concerning human nutrition remain uncertain
and unknown. After more than a century of study we still
cannot explain large observed differences in energy needs
among individuals of the same body mass and build. Be-
fore looking at some of these uncertainties, particularly in
relation to food energy requirements for basal metabo-
lism, growth, activity, pregnancy, and lactation, I review
Studies of human energy needs, conversions, and expen-
ditures were in the mainstream of the new science of en-
ergy during the pioneering decades of both theoretical
and applied research between 1840 and 1880. The con-
tributions of that time were critical in formulating the
canons of general energetics (see section 1.1). The subse-
quent invention and diffusion of small portable combus-
tion engines and electric motors (see chapters 8 and 9)
marked the beginning of the demise of humans as prime
