Historical perspective
It is known from practical experience, obtained
from the large number of polar expeditions
occurring from the middle of the last century,
that the dietary intake of indigenous people and
their domestic animals (sledge dogs) had a very
high fat content. As early as 1908, August and
Marie Krogh studied the metabolism of the
Greenland Eskimo where food consumption was
calculated, based on observations made by the
Danish explorer Rink in 1855 (Krogh & Krogh
1913). Despite such a fat-rich diet, these indig-
enous people and their dogs seemed to main-
tain normal work capacity and normal body
function.
In the laboratory, several groups of scientists
from the turn of the century have tried to eluci-
date what substrate is oxidized in muscle during
exercise. Short-term dietary changes, mostly
to fat-rich and carbohydrate-rich diets, were
applied. Zuntz et al. (1901) demonstrated that
respiratory quotient (RQ) values during mild
exercise after a fat-rich diet were of a magnitude
that suggested an almost exclusive oxidation
of fat. This was later supported by Krogh and
Lindhard (1920) and Marsh and Murlin (1928).
In the studies by Krogh and Lindhard (1920),
the subjects were asked to describe their food
intake and the perception of daily living chores
and exercise sessions while eating a fat-rich or a
carbohydrate-rich diet for 3–5 days. The subjects
almost uniformly described that exercise was
performed easily after consumption of the carbo-
hydrate diet, while exercise was performed with
severe difficulty after consumption of the fat diet.
Krogh and Lindhard (1920) also demonstrated
that the muscular efficiency, measured on a
Krogh bicycle ergometer positioned within a
Jaquet respiration chamber, was some 10–11%
more effective while carbohydrates were oxi-
dized than while fat was oxidized. These find-
ings were later supported by Hill (1924) and
Marsh and Murlin (1928).
The work by Christensen and Hansen (1939)
revealed a lower respiratory exchange ratio
(RER) during exercise and a shorter endurance
performance time at a submaximal exercise
intensity after 3–5 days’ adaptation to a fat diet
than after 3–5 days’ adaptation to a carbohydrate
diet. Thus, interest in the influence of diet on
work capacity is not new, but during the last 50
years, focus has mainly been on the role of
dietary carbohydrates for enhancing physical
performance. However, because athletes today
participate in physically demanding events of
ever-increasing duration, it has been speculated
whether habitually eating a high-fat diet could
provide some of the adaptations that are pro-
duced by habitual physical exercise and thus
improve physical performance.Endurance performance in rats
In animals, the effect of adaptation to a fat-rich
diet on endurance performance has mostly been
investigated in rodents and less often in dogs and
other animals. Studies in rats adapted to a