210 kJ · kg–1· day–1(35–50 kcal · kg–1· day–1) , 1.75 g
protein · kg–1· day–1and the remainder of calories
as two-thirds carbohydrates and one-third fat.
This was followed by 4 weeks of a eucaloric keto-
genic diet (EKD), isocaloric and isonitrogenous
with the EBD diet, but providing fewer than
20 g carbohydrates daily. The subjects continued
their normal training throughout the study.
Endurance time to exhaustion, at 60–65% V
.
o2max.,
was longer in three subjects (57%, 30%, 2%) and
shorter in two (36%, 28%) after 4 weeks’ adapta-
tion to EKD, resulting in no statistical difference
in the mean exercise time after the two dietary
trials (147±13 min for EBD vs. 151±25 min for
EKD). However, the big variability in perfor-
mance time of the subjects makes the results diffi-
cult to interpret. A highly significant decrease in
RQ values during the endurance test was found
and in agreement with this a threefold drop in
glucose oxidation and a fourfold reduction in
muscle glycogen use were demonstrated.
To summarize, so far the literature has pro-
vided a conflicting picture when the effect of
dietary fat on endurance performance is investi-
gated in man. These disparate results could be
explained by the varied research designs used,
making firm conclusions impossible. Moreover,
dietary manipulations for only 4 weeks may not
be long enough to induce adaptations in skeletal
muscle of importance for endurance exercise
capacity. Also, one might speculate whether
training status, as indicated by maximal oxygen
uptake of the subjects, could be of any signifi-
cance. In the study by Helge et al. (1998), the
interaction between training and diet was inves-
tigated. Fifteen initially non-trained male sub-
jects were randomly assigned to consume a fat
diet (62 E% fat, 21 E% carbohydrate, 17 E%
protein) or a carbohydrate diet (20 E% fat, 65 E%
carbohydrate, 15 E% protein) while following a
supervised training programme for 4 weeks.
Training was performed four times weekly and
each training session alternated between short
and long-lasting intervals at 60–85% of V
.
o2max.,
lasting 60 min. After the 4-week intervention
period,V
.
o2max.was similarly increased by 9% in
both dietary groups (P<0.05). Endurance perfor-
198 nutrition and exercise
mance time to exhaustion, measured on a Krogh
bicycle ergometer, at 72% of V.
o2max. (same
absolute power output as in the initial non-
trained trial), was similarly and significantly
increased in both dietary groups both after 2 and
4 weeks of training and dieting (Table 14.1).
Thus, comparing the trained subjects in the fat
group with those in the carbohydrate group after
4 weeks, exercising at the same relative workload
(72% of V.
o2max.), no differences in exercise time to
exhaustion were found between the two dietary
groups (79±8 min in the fat group vs. 79±15 min
in the carbohydrate group). Thus, it appears that
adaptation to a fat diet in combination with train-
ing up to 4 weeks, exercising at a submaximal
intensity (60–70% of V.
o2max.), does not impair
endurance performance (Phinney et al. 1983;
Helgeet al. 1998). However, in the study by Helge
et al. (1996), two groups of non-trained male sub-
jects underwent a 7-week supervised training
programme while consuming either a fat diet (62
E% fat, 21 E% carbohydrate, 17 E% protein) or a
carbohydrate diet (20 E% fat, 65 E% carbohy-
drate, 15 E% protein). Maximal oxygen uptake
increased similarly in the two groups by 11% (P<
0.05). Time to exhaustion, exercising on a Krogh
bicycle ergometer at 82% of pretraining V.
o2max.,
was significantly increased, from initial mean
values for the two groups of 35±4 min to 65±
7 min in the fat group, but significantly more in
the carbohydrate group (102±5 min). Thus, com-
bining these findings it is apparent that theTable 14.1Endurance performance (mean ±SE,
measured in minutes) until exhaustion before and after
2 weeks’ and after 4 weeks’ adaptation to training and
a fat-rich or a carbohydrate-rich diet.After After
Before 2 weeks 4 weeksFat-rich diet 29.5±4.3 47.8±8.1* 78.5±8.2*
Carbohydrate- 31.7±4.3 59.5±10.6* 79.3±15.1*
rich dietFrom Helge et al. (1998).
*P<0.05 compared to before values.