NUTRITION IN SPORT

increased blood insulin response and decreased
blood glucose response with the addition of
protein to a 58 g carbohydrate supplement. The
insulin response was found to be directly pro-
portional and the glucose response inversely
proportional to the protein content of the
carbohydrate–protein supplement. No adverse
side-effects were reported.
We therefore investigated the effects of a car-
bohydrate–protein supplement on muscle glyco-
gen resynthesis after exercise (Zawadzki et al.
1992). The supplements tested consisted of 112 g
carbohydrate or 112 g carbohydrate plus 40.7 g
protein (21% wt/vol mixture). The supplements
were administered immediately after exercise
and 2 h after exercise. It was found that the com-
bination of carbohydrate plus protein resulted in
a synergistic insulin response. In conjunction
with the greater insulin response was a signifi-
cantly lower blood glucose response and a 38%
faster rate of muscle glycogen storage com-
pared with carbohydrate supplementation
alone. Rates of muscle glycogen resynthesis aver-
aged 7.1mmol · g–1wet weight · h–1for the carbo-
hydrate–protein treatment and 5.0mmol · g–1wet
weight · h–1 for the carbohydrate treatment
during the 4-h recovery period (see Fig. 7.5). It
was also found that carbohydrate oxidation rates
and blood lactate concentrations for the carbohy-

106 nutrition and exercise

drate–protein and carbohydrate treatments

were similar. These results suggested that the

increased rate of muscle glycogen resynthesis

during the carbohydrate–protein treatment was

the result of an increased clearance of glucose by

the muscle due to the increased blood insulin

response. Since the carbohydrate–protein sup-

plement was palatable and there were no

unwanted side-effects, it would appear to be a

viable supplement for postexercise glycogen

recovery.

differences in

simple carbohydrates

The effect of supplements composed of predomi-

nately glucose, fructose and sucrose have also

been investigated (Blom et al. 1987). Glucose and

fructose are metabolized differently. They have

different gastric emptying rates and are absorbed

into the blood at different rates. Furthermore, the

insulin response to a glucose supplement is gen-

erally much greater than that of a fructose sup-

plement. Blom et al. (1987) found that ingestion

of glucose or sucrose was twice as effective as

fructose for restoration of muscle glycogen (Fig.

7.6). They suggested that the differences between

the glucose and fructose supplementations were

the result of the way the body metabolized these

Increase in muscle

glycogen concentration

(μ

mol

.kg

–1

wet wt)

40

20

0

0123 45 6

Time (h)

Glucose

Sucrose

Fructose

Fig. 7.6Increases in muscle

glycogen concentration when

glucose, fructose and sucrose are

provided in amounts of 0.7 g · kg–1

body weight immediately after

exercise and at 2-h intervals.

From Blom et al. (1987), with

permission.