tigated whether animals adapted to a prolonged
high-fat diet could tolerate a second bout of exer-
cise following 3 days of recovery consuming a
carbohydrate-rich diet compared with animals
adapted to a prolonged high-carbohydrate diet
after consuming a fat-rich diet. Even though
Conlee and co-workers (1990) found that fat-fed
rats ran equally long as carbohydrate-fed rats,
switching the diet for the last 3 days resulted in
better endurance performance by fat-adapted
animals switched to the carbohydrate diet for 3
days than carbohydrate-fed animals continued
on the carbohydrate diet for 3 more days. Also, in
the study by Lapachet et al. (1996), when training
was combined with diet for 8 weeks, rats ran
approximately 40% longer when the rats, after fat
adaptation, switched to the carbohydrate diet for
3 days than when the rats were fed only a carbo-
hydrate diet. Thus, in rats endurance perfor-
mance time was increased after prolonged fat
adaptation and a subsequent brief exposure to a
carbohydrate-rich diet.
In rats the literature reveals a fairly uniform
positive effect of fat-rich, virtually carbohydrate-
free diet on endurance performance in rats,
whereas there is an apparent discrepancy regard-
ing the effect of dietary fats on endurance perfor-
mance in man.
Endurance performance in man
It is well known from the classic literature that
increasing the dietary fat relative to carbohy-
drates results in increased fat and decreased
carbohydrate utilization during submaximal
exercise (Christensen & Hansen 1939). Thus, it
has been hypothesized that increasing the avail-
ability of fatty acids for oxidation might increase
the oxidation of fat and spare carbohydrate and
furthermore increase performance. Due to this
hypothesis, acute dietary and pharmacological
methods have been used to enhance the avail-
ability of fatty acids for oxidation. In the study by
Griffiths et al. (1996), eight subjects consumed
either a fat-rich meal (65 E% fat, 28 E% carbohy-
drate, 7 E% protein) or a carbohydrate meal (2
E% fat, 80 E% carbohydrate, 18 E% protein) and
194 nutrition and exercise
were followed over the next 6 h, while resting.
Prior to the fat meal the plasma concentration of
free fatty acids (FFAs) amounted to 400mmol · l–1.
One hour after ingestion of the fat meal, the
plasma concentration of FFA had decreased to
200 mmol·l–1, whereafter plasma FFA increased
continuously to 500mmol · l–1at 4 h and approxi-
mately 550mmol·l–1at 6 h. Thus, the intake of
80 g fat, as in this study, was not associated with
any particular increase in circulating fatty acids
during the following 6 h. Studies have estab-
lished that glucose feeding prior to exercise pro-
duces hyperglycaemia, inducing stimulation of
insulin secretion, which in turn depresses the
exercise-induced lipolysis and increases RQ,
indicating an increased participation of carbohy-
drates in the total energy expenditure. The ques-
tion is whether fat feeding prior to exercise
would enhance the oxidation of fat at the
expense of carbohydrate during exercise. This
question was addressed in the study by Satabin
et al. (1987). Nine trained male subjects either
were fasting or ingested a pre-exercise meal
(1.7 MJ, 400 kcal) 1 h prior to a submaximal exer-
cise test (60% of V.
o2max.) to exhaustion. The meals
contained either medium-chain triacylglycerols,
long-chain triacylglycerols or glucose. During
exercise, plasma insulin concentrations were
decreased in all conditions. The FFA concentra-
tions were increased similarly after the two lipid
meals and in the fasting situation and markedly
higher than that in the glucose trial, and RQ
was significantly lower in the lipid trials and in
the fasting condition than in the glucose trial.
Despite the enhanced fat oxidation during ex-
ercise, after the consumption of a fat meal, no
differences in endurance time (approximately
110 min) between any of the four dietary trials
were seen. Also, in studies in which intralipid-
heparin was infused during exercise, the avail-
ability of fatty acids was markedly increased. In
the study by Hargreaves et al. (1991), a sparing of
muscle glycogen during exercise was not seen,
whereas a decreased rate of glycogen degrada-
tion was found in another study (Dyck et al.
1993). Endurance performance was, however,
not measured in any of these studies. Also, the