NUTRITION IN SPORT

reduce HDL levels and, given the inverse
association between HDL cholesterol and the
risk of CHD, theoretically may diminish the
anticipated beneficial effects of decreased low
density lipoprotein cholesterol. Exercise may be
one way to offset a diet-related fall in HDL cho-
lesterol. Comparison of two different interven-
tions in sedentary overweight men and women,
i.e. a low energy, low fat diet alone with the same
diet plus exercise (brisk walking and jogging)
showed that the addition of exercise to the low
fat diet resulted in more favourable changes in
HDL cholesterol than diet alone; in men, diet
plus exercise provoked in a greater rise in HDL
cholesterol than did diet only; and in women
only the diet-plus-exercise group showed a
favourable change in the ratio of LDL cholesterol
to HDL cholesterol.
It was mentioned above that changes in
lipoproteins tend to be greater when an exercise
regimen is accompanied by weight loss. There is

48 nutrition and exercise

also an effect which is independent of weight

change, which appears to be linked to adapta-

tions in skeletal muscle. During exercise there is a

net efflux of HDL 2 across a trained leg, but not

across the contralateral untrained leg (Kiens &

Lithell 1989). The rate of HDL 2 synthesis is posi-

tively and strongly related to the rate of VLDL

degradation. As the rate-limiting step in VLDL

degradation is LPL activity, this points to skeletal

muscle LPL as an important determinant of the

effects of exercise on lipoprotein metabolism.

Postprandial lipoprotein metabolism

High levels of muscle LPL activity, leading to an

enhanced metabolic capacity for TAG may there-

fore explain the elevated HDL cholesterol levels

in physically active people. Endurance trained

men and women show high levels of plasma and

muscle LPL activity, together with high rates of

TAG clearance (compared with sedentary con-

∆

VO

2max

(ml

.kg

–1.

min

–1

)

6

0

4

2

–2 –6%

–4

+4%

+9%

+16%

Controls Strollers Brisk

walkers

Fast

walkers

(a)

∆

HDL cholesterol (mmol

–1.l

)

0

+1%

+6%

+4%

+6%

Controls Strollers Brisk

walkers

Fast

walkers

(b)

0.12

0.09

0.06

0.03

.

Fig. 3.2Changes in (a) maximal oxygen uptake (V

.
o2 max.) and (b) serum high-density lipoprotein (HDL) cholesterol
concentration in control subjects (n=10/13) and in three groups of previously sedentary women who walked 4.8
km · day–1for 24 weeks. One group walked at 4.8 km · h–1(n=17/18, strollers), one group at 6 km · h–1(n=12, brisk
walkers) and one group at 8 km · h–1(n=13, fast walkers). Adapted from Duncan et al. (1991).