Asia Pacific J Clin
Nutr (1997) 6(1): 60-62
Influence
of palm oil and palm oil fractions on protein utilisation
Christiani Jeyakumar Henry PhD, Amal Ghusain-Choueiri
PhD, Michael I Gurr PhD, FlBiol
School of Biological and Molecular
Sciences, Oxford Brookes University, Gipsy Lane, Oxford
The influence of dietary palm-oil fractions on protein
utilisation has been investigated in the growing rat. At 30 days
of age, 4-6 groups of four animals were offered one of six semi-purified
diets that differed only in the palm-oil fraction. Diets contained
200g casein, 550 g carbohydrate, and 200g fat/kg. The different
palm-oil fractions were: crude palm oil (CPO), refined palm-kernel
oil (PKO), refined palm olein (RPO), refined palm stearin (RPS),
refined palm oil (RPOL). The control groups were given Olive oil
(OO) as the dietary fat source. The conversion efficiency of dietary
protein was assessed as Net Protein Utilisation (NPU), using a 10-day
comparative carcass technique.
Weight gain and food intake were not altered by
the various palm-oil fractions. However, the NPU of rats given RPO
was significantly higher (p<0.05) than that of rats given all
other palm-oil fractions or the OO control. It is concluded that
the RPO has the potential to significantly improve NPU in the rat,
compared to four other palm-oil fractions as well as olive oil.
Introduction
For more than a century, nutritionists have been concerned
with the factors that affect protein utilisation. For example Willcock
and Hopkins1, showed that amino acid composition was a
crucial factor influencing protein utilisation. The importance of
energy intake in altering the efficiency of protein utilisation was
first demonstrated by Rubner2 in 1879. It is now generally
accepted that nitrogen balance is impaired when energy intake is inadequate3,4.
The question of whether the type rather than the amount
of non-protein energy is of any importance in affecting the utilisation
of protein is less well resolved. Munro5, synthesised all
these observations in a comprehensive review entitled ‘Carbohydrate
and Fat Factors in Protein Utilisation and Metabolism’. He concluded:
"Thus nitrogen balance undergoes temporary impairment when fat
is substituted isocalorically for dietary carbohydrate. Carbohydrates
also play a special part in conserving protein of endogenous as well
as of dietary origin, for the feeding of carbohydrate to fasting animal
reduces nitrogen output but the feeding of fat does not have this
effect until the fat stores are exhausted".
With the question of the superiority of carbohydrate
or fat as an energy source for protein metabolism unresolved, another
matter of interest was the impact of the type or nature of fat in
particular on protein metabolism. Deuel and co-workers6
reported no difference in growth in rats fed butter-, maize-, cotton
seed-, olive-, groundnut-, or soy oil. Whereas Thomasson7,
who investigated 20 different oils, concluded that there was a difference
in growth of rats fed various oils and noted that some oils in particular
(rapeseed, kapokseed) produced extremely poor growth. similarly Naismith
and Qureshi8 reported poor growth in animals fed mustard
oil. Such reports, however, are difficult to interpret in terms of
protein metabolism. While poor growth (weight gain) almost always
indicates a reduced nitrogen balance, the poor weight gain can also
result from changes in food intake, with the efficiency of nitrogen
utilisation being unimpaired. Another cause for poor growth may be
an increased energy expenditure, or a fall in food intake such that
although the efficiency of nitrogen utilisation is reduced it is a
secondary effect to energy restriction9-11.
Despite the conflicting reports and possible influence
of fat on growth, the general consensus among researchers has been
to accept that the chief function of fat is as an energy source and
thereby only influence the protein:energy ratio of the diet. However,
a preliminary study by our group has indicated that the efficiency
of protein utilisation (NPU) may indeed be influenced by the fat source.
Palm oil was observed to give a higher NPU value than butter-, sunflower-,
soy-, or olive oils12. The purpose of this study is thus,
to investigate the influence of dietary fat on protein utilisation,
with specific reference to palm oil.
Materials
and methods
Animals
and diets
Weanling male (21-23 days old) Sprague-Dawley rats
(OLAC Ltd, Shaws Farm, Blackthorn, Oxon, UK) were kept in a room maintained
between 26-28°C with a 12 hour light and dark cycle. All animals were
allowed free access to food and water.
Rats were fed the BP (Witham, Essex, UK) stock diet
for 7 days prior to the NPU assay. At 30 days of age they were divided
into groups of 4 and offered one of 6 semi-purified diets that differed
only in the palm oil fraction. The composition of the diet is given
in Table 1 (Diet P+). The fat source of each of the semi-purified
diets was as follows: crude palm oil (CPO), refined palm kernel (RKO),
refined palm olein (RPO), refined palm stearin (RPS), and refined
palm oil (RPOL). A 7th control group was offered an identical diet
but with olive oil (OO, control) as the source of fat. Two further
dietary groups were fed on free-protein diets (Diet P-,
Table 1), with either refined olein (P-RPO) or crude
palm oil (P-CPO) as the fat source.
The metabolisable energy content of the diets were
calculated to be 20.15 kJ/g (on an air-dried basis), by applying the
conversion factors of 17.0, 37.0 and 17.0 kJ/g respectively for the
energy content of protein, fat and carbohydrate.
Groups of rats matched for body weight were killed
at start of the experimental period, to provide an initial value of
total body nitrogen content. During the next 10 days (the duration
of NPU assay), each group was housed in a cage with wire mesh at the
bottom. The spilt food was collected on a plastic tray covered with
filter paper and kept underneath the cage. The powdered diet was dispensed
in glass food pots. Energy and protein (nitrogen) intakes were calculated
from the amount of air-dried food consumed multiplied by the nitrogen
content of the diets, to give the nitrogen intakes (I) of the animals.
On the 10th day of the assay period, the animals were killed by cervical
dislocation. The water content of the carcasses (including gut contents)
was determined by drying to a constant weight.
Table 1. Composition of semi-purified diets
| Ingredient |
Diet P+
(g/kg)
|
kJ/kg
|
Energy (%)
|
Diet P-
(g/kg)
|
| Palm oil fraction*/
olive oil |
200
|
7400.0
|
36.7
|
200
|
| Casein |
200
|
3400
|
16.9
|
-
|
| Sucrose/Corn-meal |
550 (8:3)
|
9350
|
46.4
|
750
|
| Vitamin and mineral
mix† |
50
|
-
|
-
|
50
|
P, protein; +, adequate; -, deficient; †
Palm oil fractions purchased from Anglia Oils Ltd, King George
Dock, Hull, UK.
*Mineral and vitamin mix obtained from SDS, Witham, Essex. UK.
Analytical
methods
Nitrogen content of carcass and
food. The dried carcasses from each group
were pooled and macerated. Samples of the finely minced carcass and
of dried food were analysed for nitrogen using the Kjeldahl method13.
Efficiency of protein utilisation.
This was calculated using the formula for Net Protein Utilisation
(NPU) described by Miller and Bender14. NPU= (B-Bk)/
I
Where B = body nitrogen of test diet fed group
Bk = body nitrogen of non-protein fed group
I = nitrogen intake of test group
Statistical
analysis
Differences between the dietary groups were analysed
using one-way analysis of variance (ANOVA). Results are expressed
as the mean and its standard deviation.
Results
Growth rate of animals fed on protein-containing diets
was not significantly altered by the source of dietary palm-oil fraction
nor by palm oil compared to olive oil (Figure 1). The food intake
of rats was similar on all the protein-containing diets, as was the
amount of nitrogen retention (Table 2). However, the NPU of rats fed
the diet containing refined palm olein was significantly higher (P<0.05)
than all the other palm oil fractions and the olive oil control (Figure
2).
Figure 1. Growth curve of rats fed on diets
containing various palm oil extracts: CPO (+ ), RPK (¨ ), RPO (6 ), RPS (s ), RPOL (D ), P-RPO (l
) P-CPO (¢ ) and OO (à ) as control, For details of dietary treatment, see Table 1. Points
are means of 4-6 trials.
Figure 2. NPU for rats fed on various palm-oil
fractions and olive oil. Values are the means with SD (n 4-6
trials each). Significantly different, ANOVA: *P<0.05.
(Legend for
figure: NPU for rats fed on various palm-oil
fractions; vertical axis is NPU value starting from 0, in increments
of 10; horizontal axis is Fat type, in order from left to right: CPO,
PKO, RPO, OO RPS, RPOL)
Table 2. Weight gain, energy intake and
Nitrogen balance in rats fed various palm oil fractions.
(Mean values and standard deviations for 4-6 groups, each of 4
rats, over a 10 d assay period)
| Dietary treatment |
Weight gain (g)
|
Energy intake (MJ)
|
Nitrogen intake (g)
|
Nitrogen retained B-Bk
(g)
|
| |
mean
|
SD
|
mean
|
SD
|
mean
|
SD
|
mean
|
SD
|
| CPO |
258
|
29.2
|
11.1
|
1.52
|
17.8
|
2.42
|
10.0
|
1.36
|
| PKO |
236
|
19.9
|
10.5
|
1.19
|
16.7
|
1.90
|
9.7
|
1.41
|
| RPO |
260
|
44.1
|
10.6
|
1.31
|
16.9
|
2.09
|
11.4
|
3.11
|
| RPS |
244
|
55.4
|
10.6
|
1.81
|
16.9
|
2.88
|
10.0
|
2.55
|
| RPOL |
240
|
27.0
|
10.2
|
1.36
|
16.3
|
2.16
|
9.9
|
1.38
|
| OO (control) |
255
|
34.1
|
10.6
|
1.88
|
17.0
|
3.00
|
10.6
|
1.91
|
Average starting weight approximately 107.5g/rat
Discussion
The dietary palm oil fraction did not influence the
amount of feed consumed by experimental animals. Thus, feed palatability
was not a factor influencing protein retention.
The rate of weight gain was also similar is all the
groups tested. A similarity in the growth rate of rats fed on diets
containing either CPO or RPO was also noted by Manorama and Rukmini15.
The NPU in the RPO-fed groups was enhanced on average
by about 15.3% compared to animals fed on any of the other 4 palm-oil
fractions. It is well known that the relative proportions of saturated
to unsaturated fatty acids (u/s) are the main determinants of an oil’s
physical and biological properties16. As compared to the
other 4 palm-oil fractions, palm olein has the highest u/s ratio (1.23
compared to 1.00, 0.57, 0.23, for RPOL, RPS, and PKO respectively17).
The digestible energy in growing pigs has been shown to improve exponentially
as a function of u/s18. Digestibility of oils can exert
an influence on NPU7. Although, nitrogen retention did
show a slight improvement in RPO-fed groups, the increase was not
statistically significant.
More recently Abe et al19, reported
that different palm-oil saturated fatty acids can exert differential
effects on various lipid parameters in the rat. Whether the same can
be said for protein metabolism is still to be investigated.
Manorama and Rukmini15 measured NPU in
weanling Wistar rats fed on 10% of either CPO or RPO for 28 days.
They could not find any significant difference in NPU between the
two oils. Furthermore, the mean NPU values they reported for the CPO-
and RPO-fed groups were respectively, 13% higher and 8% lower than
the present results. A direct comparison of those results with the
present ones is not justified since both the design and duration of
the two studies were different.
The practical implication of our studies may be summarised
as follows:
Millions of children around the world suffer from
protein-energy malnutrition of which commonest forms are kwashiorkor,
marasmus or marasmic-kwashiorkor. These are characterised by muscle
wasting, loss of adipose tissue and oedema. The routinely administered
rehabilitation formulae for catch-up growth in malnourished children
is based on the following composition: skimmed milk powder 110g, sugar
50 g, oil (usually groundnut) 60 g contained in 1L water. This liquid
diet provides 1180 kcal/L and 38.5 g protein/L.
On such a diet malnourished children tend to recover
their initial body weight within 5-6 weeks. Our results indicate that
the use of RPO enhances N balance and thus in theory, should improve
tissue accretion. A human trial, with RPO as the fat source during
nutritional rehabilitation of malnourished children, may be a practical
outcome of these studies.
Influence of palm
oil and palm oil fractions on protein utilisation
Christiani Jeyakumar Henry,
Amal Ghusain-Choueiri, Michael I Gurr
Asia Pacific Journal of Clinical Nutrition (1997) Volume 6, Number
1: 60-62
References
- Willcock EG, Hopkins FG. J of Physiol. 1906; 35:
88.
- Rubner M. Zeitschrift fuer Biologie. 1879; 15:
115.
- Calloway DH, Spector H. Nitrogen utilisation during
caloric restriction. The effect of dietary fat content. J of Nutr.
1955; 56: 533-541.
- Miller DS, Payne PR. Problems in the prediction
of protein values of diets: Caloric restriction. J of Nutr. 1961;
75: 225-230.
- Munro HN. Carbohydrate and fat as factors in protein
utilisation and metabolism. Pysiol Rev. 1951; 31: 449-487.
- Deuel HJ, Movitt E, Hallam L, Mattson FH. Studies
on the comparative nutritive values of fats. I. Growth rate and
efficiency of conversion of various diets to tissue. J of Nutr.
1944; 27: 107.
- Thomasson HJ. The biological value of oils and
fats. I. Growth and food intake on feeding with natural oils and
fats. J of Nutr. 1955; 56: 455.
- Naismith DJ, Qureshi RU. The role of dietary fat
in the utilization of protein. I quality and quantity of fat. J
of Nutr. 1962; 77: 373-380.
- Rafael J, Patzelt J, Elmadfa I. Effect of dietary
linoleic acid and essential fatty acid deficiency on resting metabolism,
nonshivering thermogenesis and brown adipose tissue in the rat.
Journal of Nutrition 1988; 118: 627-632.
- Yazbeck J, Goubern M, Senault C, Chapey MF, Portet
R. The effects of essential fatty acid deficiency on brown adipose
tissue activity in rats maintained at thermal neutrality. Comparative
Biochem and Physiol. 1989; 94A: 273-276.
- Henry CJK, Ghusain-Choueiri A, Payne P. Protein
utilization, growth and survival in essential-fatty-acid-deficient
rats. Br J Nutr. 1996; 75: 237-248.
- Henry CJK, Gurr MI. Workshop on Lipids PORIM, Kuala
Lumpur, 1995.
- Bradstreet R. The Kjeldahl method for organic nitrogen.
New York/London, Acad Press, 1965.
- Miller DS, Bender AE. The determination of the
net utilisation of proteins by a shortened method. Br J Nutr. 1955;
9: 382-388.
- Manorama R, Rukmini C. Nutritional evaluation of
crude palm oil in rats. Am J Clin Nutr. 1991; 53: 1031s-1033s.
- Cottrell RC. Introduction: Nutritional Aspects
of Palm Oil. Am J Clin Nutr. 1991; 53: 989s-1009s.
- MacFarlane N, Swetmen AA, Coursey DG. Comparison
of Traditional and Industrial Palm Oil. Palm Oil News 1984; 28:
11-17.
- Powels J, Wiseman J, Cole DJA, Hardy B. Effect
of chemical structure of fats upon their apparent digestible energy
value when given to growing-finishing pigs. Animal Production 1993;
57 (pt1): 137-146.
- Abe K, Imaizumi K, Sugano M. Effects of different
triglyceride saturated fatty acids on tissue lipid level, fatty
acid composition, faecal steriod excretion, prosta-cyclin production
and platelet aggregation in rats. Biosci, Biotech and Biochem. 1993;
57: 247-252.
Copyright © 1993 [Asia Pacific Journal of Clinical
Nutrition]. All rights reserved.
to the top
HEC
PRESS Publisher
of the 
