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Research Article

Comparison Between the Effects of Saturated and Unsaturated Oils on Serum Cholesterol of Jordanian Volunteers

Abdullah Y. A. Rawashdeh
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The effect of palm oil (PO), olive oil (OO), corn oil (CO) and soybean oil (SO) on the serum lipid profile was studied in 24 healthy persons (12 males, aged 35-43 y; 12 females, aged 26-34 y). The subjects ate their habitual diet using one type of oil in food preparation for 4 weeks with 4 weeks interval between the four oil periods. The SO, CO and OO-diets were significantly (P<0.05) reduced levels of serum total cholesterol, low and high density lipoprotein cholesterol, whereas PO diet caused slight increase in this levels. However, SO-diet caused comparatively higher reduction in these levels (-11, -9.5, -2 mg dl-1, respectively). Triglycerides level was increased after SO, CO and OO periods, while PO diet reduced this level.

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Abdullah Y. A. Rawashdeh , 2003. Comparison Between the Effects of Saturated and Unsaturated Oils on Serum Cholesterol of Jordanian Volunteers. Pakistan Journal of Biological Sciences, 6: 580-586.

DOI: 10.3923/pjbs.2003.580.586



Clear relation has been evident between blood cholesterol concentration and individual risk of coronary heart disease (CHD) (Cottrell, 1991). Most CHD is due to the blockages in arteries supplying blood to the heart muscle, as a result of depositing more fat and cholesterol over the years. The arteries become narrower and narrower, this process is known as atherosclerosis (Williams, 1993). Severe disability from all forms of CHD are responsible for the highest incidence of morbidity and mortality recorded for any disease state in many developed nations (Hetzel et al., 1989). Cholesterol like other fatty substances cannot mix with water. Therefore, to carry cholesterol and other lipids in the blood, the body wraps them in protein packages. This combination is called a lipoprotein. Blood cholesterol is found in all lipoproteins, including the low density lipoproteins (LDLs) and high density lipoproteins (HDLs) (Williams, 1993). LDLs contain the greatest amount of blood cholesterol and may be responsible for depositing cholesterol in the artery walls. These lipoproteins are atherogenic (Wang, 1987). HDLs contain the greatest amount of protein and small amount of cholesterol. HDLs can acquire cholesterol from cells and transport it to the liver for the reprocessing or bile acid formation (Koo et al., 1985). These lipoproteins are appearing to be antiatherogenic (Wang, 1987).

Blood cholesterol concentration can be changed in individuals by alterations in the fatty acid content of their dietary fat (Raiser, 1973). An increase in saturated fatty acids in the diet may lead to an increase in blood cholesterol content (Banamon and Grundy, 1988). The longer chain fatty acids (≥ C18) seem to have little effect, whereas the medium chain fatty acid (C10-C16) have a hypercholesterolemic effect (Dziezak, 1989; Elson, 1992; Sundram and Basiron, 1994). The monounsaturated fatty acids (MUFAs) like oleic acid, which preponderant in olive oil, may reduce the blood cholesterol level (Baggio et al., 1988). The Polyunsaturated fatty acids (PUFAs), including the essential fatty acids (EFAs), are thought to have a blood cholesterol lowering effect when taken in the diet (Tany et al., 1991; Jones, 1994). Besides that, the PUFAs, may reduce the concentration of blood LDL_cholesterol (LDL_c) and HDL_cholesterol (HDL_c) (Nestel, 1987). More specific, dietary n-3 PUFA are more potent than n-6 PUFA in reducing the serum cholesterol (Hearn et al., 1987). N-3 PUFA have several beneficial cardiovascular properties (Stone, 1996), including antiatherothrombogenic, antiarrythmic and antihypertensive effects (Grundt et al., 1995).

The aim of this study was to determine the effect of four different types of oil, saturated oil such as palm oil (PO), monounsaturated oil such as olive oil (OO), polyunsaturated oil such as corn oil (CO) and soybean oil (SO), on Jordanian blood lipid profile.

Materials and Methods

Participants in this study were selected from different locations in Jordan (Amman, Karak) from Apr. to Nov., 2001. Twelve males averaged 36 years old (ranged 35-43 y.) and twelve females averaged 28 years old (ranged 26 -34 y.) were included in this study. Body weight and body mass index of males were 63 Kg and 21.8, respectively and of females were 56 Kg and 21.3, respectively. All subjects were healthy, normocholesterol level (< 200 mg dl-1), normotensive, non diabetic and free from cardiac, renal, hepatic or bleeding disorders. However, this study was depended on the families (husband and wife) and they were supplied the mentioned oils and asked to maintain their dietary habits with changing only in the oil type used in food preparation.

Diets: Bread (twice a day) and rice (four times a week) were contributing as the main source of carbohydrates, while chicken (twice a week) and eggs (three eggs a week) were contributing as the main source of protein. Milk and its products (three times a week) and meat were eaten once a week. Different green vegetables and fruits were eaten four times and twice a week, respectively. Daily meals were based on a seven days rotation menu; the same menu was maintained throughout the study. The only variable was the type of oil used in cooking or dipping. PO, Crude OO, CO and SO were used in the preparation of participant diets. Fatty acid composition of these oils were shown in Table 1. Three-day-diet-record for individual dietary intake was used in this study (Table 2), macronutrients and energy were calculated using food composition tables (Pellet and Shadarvian, 1970). Current study was noted that Jordanians consumed OO more than any other oil or fat. It is usually used at least twice a day, consistently for breakfast and lunch especially with chickpea and thyme and sometimes used for cooking.

Study design: Before the beginning of the study the nutritional status of subjects was studied, this work showed that no worth mentioned different in food intake of individuals from week to week and they asked to maintain their traditional 7-days rotation menu. The 24-persons were eating their food with PO or OO or CO or SO as the sole source of fat type for 4wk with 4wk interval between the four diets. However, the period of 4wk was chosen as it has previously been shown that plasma lipid levels stabilize within 2-3 wk after initiating a change in dietary fat intake (Bonamon and Grundy, 1988). Fasting venous blood samples (10 ml) were collected at the entry and at the end of each dietary period for next analysis.

Chemical analysis:
Fatty acids composition (FA): Oil samples were saponified and the free fatty acids were methylated following the procedure of Morrison and Smith (1962). Fatty acid methylesters were separated by Hamlet Packard gas chromotography model 5710a equipped with flame ionization detectors and column of 10% DEGS on chromosorb WDMCS (Supelco, Inc.). The flow rate of carrier gas was 24 ml of N2/min, of detectors were 30 ml of H2/min and 300ml/min of air. The initial columns temperature was 150°C then raised to 180°C @ 6°C /min, the injector and detector temperature were 200 and 250°C, respectively. The identification of individual FA was made using FA-methyl ester standards to establish relative retention time. The relative content of each FA-methyl ester was reported as percent area of total FA- methyl ester.

Serum total cholesterol was determined using the enzymatic method from Arab Company for medical diagnostic, (Jordan). Triglycerides were determined by the enzymatic technique from Biocon, (Germany). HDL-c was analyzed by the precipitation technique using magnesium chloride and phosphotungestic acid from Biocon, (Germany). LDL-c was calculated using the formula.

Statistical analysis: The Completely Randomized Design was used for each parameter. Differences between means were determined using Duncan’s multiple range test at p < 0.05 by SAS (1986).

Results and Discussion

Food consumption: The fatty acid compositions of PO, OO, CO and SO are presented in Table 1. PO contained the more SFA (52.1%) than the other oils. It contained 45.4% palmitic acid. OO was highly MUFA (67.2%) in comparison with other oils. It contained 66.4% oleic acid. CO and SO contained higher PUFA (54.4 and 63.1%, respectively). They contained more than 50% linoleic acid, which is considered nutritionally an essential and adequate for human requirements. The ratios of PUFA : SFA (p:s) and MUFA + PUFA (m+p):s have been used by nutritionists to interpret the effect of dietary oil and fat on the level of blood cholesterol (Hodson et al., 2001).

Table 1:
Fatty acid profile of palm oil (PO), olive oil (OO) , corn oil (CO) and soybean oil (SO)
*SFA, saturated fatty acids; MUFA, mono unsaturated fatty acids; PUFA, polyunsaturated fatty acids.

Table 2: Food consumption of subjects
* PO, palm oil; OO, olive oil; CO, corn oil; SO, soybean oil.

Table 3:
Effects of dietary palm oil (PO), olive oil (OO), corn oil (CO) and soybean oil (SO) on concentrations of serum lipids of males and females(1)
(1) Mean ± SD, (2) :TC, total cholesterol; LDL-c, low density lipoprotein cholesterol; HDL-c, high density lipoprotein
cholesterol ; TG, triglycerides. * Significantly different from initial value P < 0.05.

Table 4:
Serum lipid responses (mg/dl and %) from the base line of males and females fed dietary Palm oil (PO), olive oil (OO), corn oil (CO) and soybean oil (SO)
* TC, total cholesterol; LDL-c, low-density lipoprotein cholesterol; HDL-c, high-density lipoprotein cholesterol.
Values in columns with different superscripts differ significantly, P<0.05.

The results showed that the p:s ratios of PO, OO, CO and SO were 0.2, 0.63, 3.58 and 5.58, respectively and the m+p:s ratios of these oils were 0.92, 3.98, 5.58 and 7.85, respectively.

The three-days-diet-record of dietary intake of participants showed no big difference in food intake between the pretrial period and the period of study and no worth mentioned difference between periods of the study. Food consumption of four diets was compared for both sexes (Table 2). It was generally higher in males than that for females. However, investigated oils formed about 60%, but SO formed about 55%, of the dietary fat intake.

Serum lipids: The consumption of OO, CO and SO significantly lowered the serum cholesterol level under the initial level, whereas PO feeding caused slight increase in this level above the initial level. However, SO resulted in more reduction in serum cholesterol level (-11mg/l) than CO (7.5 mg l-1) and OO (-4mg l-1) (Table 3). By comparison with initial concentration, OO, CO and SO significantly lowered LDL-c and caused slight reduction in HDL-c, whereas PO caused slight increase in these levels. When the responses in serum total cholesterol in the males and females were considered separately for the four diets, the reduction was greater in males than in females. The level of triglycerides (TG) was increased in serum of both sexes fed OO, CO and SO diets and in females fed PO diet, whereas decreased in males fed PO diet (Table 4).

This study had maintained the habitual diet of volunteers, for that no change in habitual diet items, but the type of dietary oil was changed to assess the effects of PO, OO, CO and SO feeding on serum lipid profile. The volunteers were able to maintain their body wieght for the study period which indicated that there was no any change in their energy balance, that was presumably due to that the subjects might have adapted their diets.

Looking back to the data in Table 1, the results indicate that all samples which show hypocholesterolemic effect have high PUFAs (specially SO) and possess high p:s and m+ p:s ratios as compared with effect of PO which contained high SFA. Among the four oils, effect of SO on serum cholesterol was more pronounced. This oil comes the first hypocholesterolemic effect, may be due to its high p:s ratio (Lee et al., 1989). It is possible that the high content of total PUFAs in SO works as an inhibitor for hepatic hydroxy-methyl-glutarate (HMG)-Co A reductase, the rate limiting enzyme in cholesterol biosynthesis (Yaquoob et al., 1995). It seems that n-3 PUFAs have high inhibition effect of this enzyme (Elson, 1992). One of n-3 PUFAs the linolenic acid which formed 8.5% of SO. Philipson et al. (1985) stated that ingesting n-3 PUFAs reduced human serum cholesterol. Therrien (1989) reported normal blood cholesterol level of Eskimo population who are famous in consuming highly marine fish diet (high n-3 PUFAs). Recently, ) stated that (n-6 PUFAs ) Hodson et al. (2001) reduced serum cholesterol in human. One of these fatty acids, the linoleic acid which formed 54.6% in SO and 53.5% in CO. Chanmugan et al. (1986) and Hearn et al. (1987) mentioned that the concentration of serum cholesterol tended to increase linearly with the increase in n-6 PUFAs/n-3 PUFAs (n-6/n-3) ratios. Furthermore, Elson (1992) showed that with the decrease in n-6/n-3 ratios, the serum cholesterol and hepatic HMG-CoA reductase activities were also lowered. These explanations may presumably explain the hypocholesterolemic effect of all PUFA and at the same time emphasize the high effect of n-3 PUFA. However, these explanations may also enhance the idea about imaginable role of SO in reducing the serum cholesterol of human being, specially SO that contains high percentage of linolenic acid. CO diet which has high PUFAs comes the second in reducing effect of serum cholesterol following SO diet and this may be due to its lower content of linolenic acid (0.9 %) compared with SO.

Linoleic acid may act as a hypocholesterolemic agent in human and the same observation was found in rats (Lacono and Dougherty, 1991) in cebus monkeys (Fine et al., 1981). The SO and CO diets, resulted in decreasing the occurrence of enterohepatic circulation of bile acids and less feed back inhibition of bile acid synthesis (Bjorkhom et al., 1978). The effects of CO and SO on serum cholesterol concentration are in agree-ment with results found in human (Hodson et al., 2001; Nilsen et al., 2001), OO occupied the third in lowering effect of serum cholesterol following CO and SO. The hypocholesterolemic effect of OO diet may be attributed to its high oleic acid content, (Grundy 1989). The effect of OO diet on serum cholesterol is in agreement with results of Hodson et al., (2001). The moderate effect of PO (normocholesterolemic effect), inspite of its high SFA content and low p:s ratio, may be due to its high palmitic acid content (Sundram and Basiron, 1994). However, the slight increase in serum cholesterol after PO period may be attributed to the small amount of meyristic acid (1.3%) in PO. This type of fatty acid works as raising factor for serum cholesterol (Elson, 1992). The results of PO effects on serum cholesterol came in agreement with those obtained by Sugano and Imaizumi, (1991), whereas in disagreement with the results of Jian et al., (1997) who mentioned that PO significantly reduced serum cholesterol of human.

The effects four oils on serum TC seemed to be in accordance with their effects on HDL-c and LDL-c concentrations. The SO and CO resulted in more reduction in these concentrations than that caused by OO, whereas PO caused a slight increase in these concentrations. These differences may be attributed to the difference in fatty acid composition of the four oils. High content of PUFA in SO and CO may result in reducing the LDL-c by altering the LDL composition or by decreasing the concentration of LDL particles (Vega et al., 1982). Williams et al. (1986) reported that PUFA reduced blood lipoprotein concentrations compared with MUFA and SFA. The same observations were mentioned by Howard et al. (1995) and Noakes and Clifton (1998). Current results about the effects of dietary oil type on cholesterol of serum lipoproteins came in agreement with the results of Lu et al. (1997) and Hodson et al. (2001).

In general, the elevated blood cholesterol is a major risk factor for CVD (NCEP, 1993). Several studies confirmed that the high blood cholesterol in young adults is a predict of CVD risk in later life (Myers et al., 1995). Present results showed that replacing PO with SO rather than CO and OO is more efficacious of lowering the predicted risk of CVD due to a larger decline in serum total cholesterol. There is a good evidence that the ratio of TC/HDL-c is a better indicator of CVD risks than either total cholesterol or LDL-c alone (Kinosian et al., 1994). Results of this study showed a reduction in TC/HDL-c ratio after SO, CO, OO and PO periods. These reductions were pronounced in males than females. The results also showed that the LDL-c/HDL-c ratio was in accordance with the former ratio.

The results showed that the effect of dietary fat type on the serum TG was reverse of the effect on serum total cholesterol. That is the hypocholesterolemic effect of SO, CO and OO accompanied with an increase in serum TG level whereas PO resulted in reduction in this level. Therefore, these results imply that the differences in fatty acids composition of oil types may result in differences in their effects on secreting and degrading serum TG. PUFA and MUFA may enhance very low density lipoprotein (VLDL)- TG secretion compared with SFA(Heimberg and Wilcox, 1972). Lee et al. (1989) Stated that the plasma TG of rats increased with increasing p:s ratio. Present results are in agreement with observations of Marzuki et al. (1991), whereas in disagreement with the results of Tany et al. (1991), who mentioned that the CO reduced plasma TG of volunteers compared with PO.

In conclusion, the current results imply the hypocholesterolemic effect of unsaturated oils and distinguish the effect of n3-fatty acid (SO), which resulted in more reduction in serum cholesterol and serum cholesterol indices. Finally, this work suggests study effects of mentioned oils on serum lipid of hypercholesterolemic humans.

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