In¯uence of amount and type of dietary fat on plasma
cholesterol concentrations in goats
A.C. Beynen
a,b,*, J.Th. Schonewille
a, A.H.M. Terpstra
baDepartment of Nutrition, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 16, 3584 CM Utrecht, Netherlands bDepartment of Laboratory Animal Science, Faculty of Veterinary Medicine, Utrecht University,
Yalelaan 2, 3584 CM Utrecht, Netherlands
Accepted 13 June 1999
Abstract
Adult, non-pregnant, dry goats were fed diets differing in the amount and type of fat. To modulate the type of dietary fat, rations containing either palm oil or olive oil were used, the amount of fat being 86 g/kg dry matter (DM). To modulate the amount of dietary fat, the oils were replaced by an isoenergetic amount of native corn starch so that the dietary fat concentration dropped to 26 g/kg DM. The high fat diets, when compared with the low fat diet, signi®cantly raised plasma total cholesterol by 91%, high-density lipoprotein (HDL) cholesterol by 100%, triglycerides by 47% and phospholipids by 57%. On an average, dietary palm oil versus olive oil signi®cantly increased plasma total cholesterol by 6%, HDL cholesterol by 9% and phospholipids by 4%, but left plasma triglycerides unchanged. This study shows that plasma lipid concentrations in goats respond to the amount and type of fat in the diet.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Goats; Palm oil; Olive oil; Cholesterol
1. Introduction
In the course of our studies on dietary effects on lipid metabolism in goats, we found that isoenergetic replacement of hay by a concentrate enriched with a mixture of calcium oleate and palmitate caused a marked increase in plasma cholesterol concentrations (Van den Top et al., 1994). Hay is a complex feedstuff so that the dietary replacement was not well de®ned. In the present experiment we again looked at the
cholesterolemic effect of extra fat in the diet of goats, but the fat was now substituted for an isoenergetic amount of native corn starch.
When compared with an isoenergetic amount of digestible carbohydrates, dietary palmitic acid raises plasma cholesterol in humans, whereas, oleic acid has no, or a slight lowering effect (Grundy, 1986; Mensink et al., 1989). Thus, it could be suggested that the hypercholesterolemic effect of dietary oleate plus palmitate seen earlier in goats (Van den Top et al., 1994) was caused by palmitate rather than by oleate. This suggestion was put to the test in the present study. Apart from the diet rich in native corn starch, goats were also fed diets containing either palm oil or olive *Corresponding author. Tel.: 31-30-253-4002; fax:
31-30-253-1817.
E-mail address: [email protected] (A.C. Beynen).
oil which essentially involves of a comparison of palmitic and oleic acid. Blood samples were taken at various intervals and plasma lipids were deter-mined.
2. Materials and methods
2.1. Animals and experimental design
Eleven, non-pregnant, Dutch White dairy goats with mean body weight of 58.8 kg (SE2.19) were used. The female goats were aged 2±3 years and had been pregnant and in lactation for up to 2 times. The trial was a combination of an A1±B1±A2± B2and a cross-over design (Fig. 1). During the two A periods, all goats received the diet rich in native corn starch. During the two B periods, the diets containing either palm oil or olive oil were fed according to a
cross-over design. Thus, the A2period can be con-sidered a wash-out period within the cross-over design. Each feeding period lasted 21 days. The animals were randomly assigned to the order of the two B treatments so that there were either 5 or 6 goats in half of the cross-over experiment. During the experiment, the animals were housed individually in cages with slatted ¯oors. The cages were placed in a stanchion barn.
2.2. Diets
During the two A periods, the diet consisted of pelleted straw (diameter10 mm) and the starch-rich concentrate. During the B periods, the starch compo-nent of the concentrate was replaced by an isoener-getic amount of either olive or palm oil. The ingredient compositions of the concentrates, which were in pel-leted form (diameter5 mm), are shown in Table 1. Fig. 1. Experimental design.
Table 1
Composition of the experimental concentrates
Experimental diet
Native corn starch Olive oil Palm oil
Constant componentsa(g) 915 915 915
Native corn starch (g) 255 ± ±
Olive oil (g) ± 85 ±
Palm oil (g) ± ± 85
Total (g) 1170 1000 1000
aThe constant components consisted of (g): beet molasses, 50; soybean meal, 350; beetpulp, 250; linseed expeller, 100; maize, 150;
CaHPO4, 5; NaCl, 5; premix, 5. The premix consisted of (mg): CaCO3, 4713.2; CuSO45H2O, 15; CoSO47H2O, 0.5; Na2SeO35H2O, 0.5;
KIO3, 0.8; MnSO42H2O, 120; ZnSO4H2O, 80; retinyl acetate preparation, 10 (5000 IU); cholecalciferol preparation, 10 (1000 IU); dl-a
The replacements were done on a net energy basis (NEl).
The animals were fed individually. The component and analyzed composition of the whole diets is shown in Table 2. On an energy basis, the rations provided approximately the requirements for maintenance. The rations were offered twice daily in two equal portions at 08.00 and 17.00 h. Feed refusals, if any, were recorded daily.
2.3. Collection of samples
The experimental feedstuffs were sampled every week during the entire experiment. The pooled feed samples were ground and stored in a sealed jar at room temperature (188C).
Blood samples were taken on the last days of the A periods and on days 3, 7, 14 and 21 of the B periods. Between 10.00 and 11.00 h, blood was sampled from the jugular vein into heparinized tubes. The hepar-inized blood samples were centrifuged for 15 min at approximately 2700 x g, and the plasma was collected and stored atÿ188C.
2.4. Analytical methods
Plasma cholesterol (Allain et al., 1974), triglyceride (Bucolo and David, 1973), and phospholipid concen-trations (Takayama et al., 1977) were measured enzy-matically on an autoanalyzer (Cobas Bio, Roche, Switzerland). Plasma very-low-density and low-den-sity lipoproteins (VLDLLDL) were precipitated
with phosphotungstic acid/MgCl2 (Sigma Diagnos-tics, St Louis, MO, catalogue number 352-4) accord-ing to Assman et al. (1983), and the supernatant (high-density lipoproteins, HDL) was assayed for choles-terol. The concentration of cholesterol in VLDLLDL was calculated as the difference between whole serum and HDL cholesterol. This procedure to determine HDL cholesterol in goat plasma was ®rst compared with the measurement of HDL cholesterol after isolation of HDL by ultracen-trifugation. HDL cholesterol concentrations were measured in four goat plasma samples by using the precipitation method (Assman et al., 1983) and the density gradient ultracentrifugation procedure (Terp-stra et al., 1981).
Aliquots of the diets were placed in a vacuum oven at 70oC or 550oC and the dry matter and the ash content, respectively, were measured. Nitrogen in the diets was measured with the Kjeldahl method (IDF, 1986); a factor of 6.25 was used to convert nitrogen into crude protein. The crude ®bre content of the feedstuffs was estimated using the Fibertec System M2 (Tecator, Stockholm, Sweden). Crude fat was determined by extraction with the Soxleth method (AOAC, 1984).
2.5. Statistical analysis
Data from the last day of each feeding period, were used to evaluate the effect of replacement of native corn starch by fat. Thus, the data for the feeding of olive and palm oil were pooled. Because the factor Table 2
Components of the experimental diets and the analysed chemical composition
Experimental diet
Native corn starch Olive oil Palm oil
Components
Wheat straw pellets (g/goat.day) 350 350 350
Starch-rich concentrate (g/goat.day) 760 ± ±
Concentrate with olive oil (g/goat.day) ± 650 ±
Concentrate with palm oil (g/goat.day) ± ± 650
Analysed composition of the whole diet
Dry matter (g/kg) 912 916 920
Crude protein (g/kg DM) 175 196 196
Crude fat (g/kg DM) 26 84 88
Crude ash (g/kg DM) 80 88 88
period did not contribute signi®cantly (F-test) to the variance of plasma cholesterol concentrations, Stu-dent's pairedt-test was used to compare values for the starch diet versus fat-rich diets. To disclose the effect of type of fat, data for the feeding of either olive or palm oil were subjected to repeated measures ANOVA with goat, experimental period and diet as factors. The level of statistical signi®cance was preset atP< 0.05.
3. Results
3.1. Feed intake and body weight
The goats consumed all feed supplied. Throughout the experiment, the goats gained body weight (on an average 60 g/day). Mean ®nal body weight was 63.5 kg (SE1.97; n11) which was statistically signi®cant (P< 0.001; Student's paired t test) from pre-experimental values.
3.2. Measurement of HDL cholesterol
HDL cholesterol was measured either by the pre-cipitation or ultracentrifugation method. Table 3 docu-ments that the two methods gave similar results, which supports the use of the precipitation method in the present feeding trial.
3.3. Fat feeding and plasma lipids
Table 4 shows that the feeding of fat at the expense of native corn starch had a signi®cant impact on the plasma lipid pro®le of the goats. Fat feeding raised plasma total cholesterol by 91%, phospholipids by 57% and triglycerides by 47%. Almost 80% of the increase in plasma total cholesterol was located in the HDL fraction.
3.4. Type of fat and plasma lipids
When the goats were fed the diet containing palm oil, plasma total cholesterol concentrations were slightly, but systematically and also signi®cantly, higher than when they were given the diet with olive oil (Table 5). The increase in plasma total cholesterol as induced by palm oil feeding was on an average 6% and was fully accounted for by the increase in HDL cholesterol. Palm oil versus olive oil did not affect plasma triglycerides, but signi®cantly raised phospho-lipids by on an average 4%.
4. Discussion
Earlier work has demonstrated that the addition of cholesterol to the diet of adult, ruminating (Dougherty et al., 1982) or young, non-ruminating goats (Kenealy et al., 1977; Richard et al., 1990) produced marked increases in plasma cholesterol concentrations. The feeding of cholesterol to adult goats at a level of 100 mg/kg body weight, did not change the distribu-Table 3
HDL cholesterol concentrations in four goat plasma samples measured by the precipitation method and the ultracentrifugation method
Plasma HDL cholesterol concentration (mmol/l)
aVLDL and LDL in plasma were precipitated with
phospho-tungstic acid/MgCl2 and the cholesterol concentration in the
supernatant (HDL) was measured.
bHDL (density > 1.063 kg/l) were isolated by density gradient
ultracentrifugation and the cholesterol concentration in the HDL fraction was measured.
Table 4
Plasma lipid concentrations when the goats were fed either the diet rich in native corn starch or the two fat-rich dietsa
Native corn starch
Olive or palm oil
Plasma cholesterol (mmol/l) 1.370.08 2.620.15c HDL cholesterol (mmol/l) 0.990.08 1.980.16c VLDLLDL cholesterol (mmol/l) 0.380.04 0.640.09b Plasma triglycerides (mmol/l) 0.190.02 0.280.04c
Plasma phospholipids (mmol/l) 1.370.07 2.150.13c
aValues are meansSE (n11) after feeding the
experi-mental diets for 3 weeks.
bP< 0.05 (statistical comparison with a Student's pairedt-test). cP< 0.001 (statistical comparison with a Student's paired
tion of cholesterol between the various lipoprotein fractions. Feeding cholesterol at a level of 250 mg/kg body weight, however, resulted in a pronounced increase in LDL cholesterol rather than HDL choles-terol (Dougherty et al., 1982). As far as we know, the cholesterolemic effect of amount and type of dietary fat, as sole variables, has not been studied in goats. In this study, we used adult, ruminating goats and estab-lished the in¯uence of isoenergetic substitution of fat for starch and that of palm oil versus olive oil on plasma lipoprotein±cholesterol concentrations.
Substitution of palm oil or olive oil for native corn starch in the diet produced a dramatic increase in plasma cholesterol concentrations in the goats. Similar results have been published for other animal species, including rats (Beynen, 1987). It appears that rumi-nants and non-rumirumi-nants show similar cholesterole-mic responses to fat feeding. However, humans may show a differential response. Replacement of carbo-hydrates by palm oil will raise plasma cholesterol concentrations in man, but replacement by oilive oil will not (Grundy, 1986; Mensink et al., 1989). So far, the mechanism by which fat feeding affects plasma cholesterol concentrations remains obscure.
In the goat, as in several other animal species, but not in humans, a substantial portion of plasma cho-lesterol is located in the HDL fraction (Terpstra et al., 1982). Fat feeding caused an increase in HDL cho-lesterol and also in plasma total phospholipids. This observation may relate to the fact that phospholipids
are essentially carried by the HDL particles (Terpstra, 1985). Thus, it may be that fat feeding in goats elevates the number of HDL particles. An increase in fat intake at the expense of carbohydrates will lead to an enhanced ¯ux of fatty acids through the circula-tion. The enhanced ¯ux is illustrated by the increase in plasma triglycerides as was found in the post prandial state of the goats given the fat-rich diets. Plasma triglycerides carried by either chylomicrons or very-low density lipoproteins are hydrolysed by lipoprotein lipase which is located on the endothelial cells of adipose tissue and muscle. An increase in breakdown of plasma triglycerides causes an increase in HDL because during lipoprotein lipase mediated hydrolysis of triglyceride rich lipoproteins, surface lipids and apoproteins are transferred to HDL (Goldberg, 1996). It can be concluded that the increase in HDL levels seen after fat feeding in the goats is the result of the enhanced ¯ux of fatty acids.
Dietary saturated versus mono-unsaturated fatty acids raise plasma cholesterol levels in man (Khosla and Sundram, 1996; Mattson and Grundy, 1985; McNamara, 1992; Mensink and Katan, 1989) and in animals like rabbits (Beynen et al., 1987; Masi et al., 1986) and hamsters (Jones et al., 1990; Kurushima et al., 1995). In pigs (Seiquer et al., 1994) and guinea pigs (Fernandez and McNamara, 1989) there was no such differential effect on plasma cholesterol levels. In rats, on the other hand, dietary olive oil increases plasma cholesterol compared with saturated fat (Bey-Table 5
Plasma lipid concentrations when the goats were fed the diets containing either olive or palm oila
Dietary fat Time on the diets (days) Pooled SEM Pvalueb
3 7 14 21
Plasma cholesterol (mmol/l) Olive oil 1.69 1.96 2.52 2.54 0.049 0.002 Palm oil 1.82 2.10 2.60 2.71
HDL cholesterol (mmol/l) Olive oil 1.22 1.46 1.78 1.90 0.077 0.024 Palm oil 1.26 1.66 1.93 2.07
VLDLLDL cholesterol (mmol/l) Olive oil 0.47 0.50 0.74 0.64 0.060 0.996 Palm oil 0.56 0.44 0.67 0.64
Plasma triglycerides (mmol/l) Olive oil 0.24 0.22 0.25 0.27 0.023 0.174 Palm oil 0.26 0.24 0.28 0.29
Plasma phospholipids (mmol/l) Olive oil 1.67 1.92 2.11 2.11 0.056 0.022 Palm oil 1.81 2.01 2.15 2.16
nen, 1987; Kris-Etherton et al., 1984). Palm oil con-tains about 49% of total fatty acids in the form of the saturated fatty acid, palmitic acid. Olive oil contains 74% of oleic acid, which is mono-unsaturated. In the goats, palm oil versus olive oil, slightly but signi®-cantly, raised plasma total and HDL cholesterol con-centrations, and also plasma phospholipids. The mechanism underlying the hypercholesterolemic action of dietary saturated fatty acids is still unknown.
5. Conclusion
This study shows that plasma lipid concentrations in adult goats fed wheat-straw based rations, respond to both the amount and type of fat in the diet. Goats may thus be used to study basic aspects of dietary control of plasma lipids. The relationship between plasma lipid concentrations and health and/or production of goats is not known.
Acknowledgements
We acknowledge Jan van Dasselaar, Irene Heyloo and Jeannet op `t Eijnde for biotechnical assistance and Jan van der Kuilen and Xandra Fielmich for analytical assistance.
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