**7. Mechanism of action of red palm oil in improving the immune status of patients with AIDS and TB**

Several studies have illustrated that red palm oil (RPO) is a rich cocktail of lipid-soluble antioxidants such as carotenoids (mostly α- and β-carotene, lycopenes), vitamin E (in the form of α- , β-, δ- tocotrienols and tocopherol) and ubiquinone (mostly coenzyme Q10) (Ebong *et al*., 1999; Edem, 2002; Van Rooyen *et al*., 2008).

Feeding experiments using various animal models have highlighted that red palm oil is beneficial to health by reducing oxidative stress (Ebong *et al.*, 1999). Many studies have demonstrated the protective effects of red palm oil in a cardiac ischaemia/perfusion model of oxidative stress (Esterhuyse *et al*., 2005; Bester *et al*., 2006; Engelbrecht *et al.,* 2006) and modulation of the serum lipid profile in rats.

RPO is widely used as cooking oil in West and Central Africa and plays an essential role in meeting energy and essential fatty acid needs in many regions of the world. It contains many beneficial antioxidants and micronutrient compounds such as tocopherol, tocotrienol, lycopene, squalene, co-enzyme Q10, physterol, glycolipids, phosphatides, calcium, phosphorus, iron, riboflavin, chlorophil, xanthophil, flavonoids, phospholipids, and carotenoid in addition to the equal proportion of saturated and unsaturated fatty acids such as oleic acid, linolenic acid, palmitic acid, linoleic acid, stearic acid and arachidic acid. It is known to be the richest source of carotenoids in terms of provitamin A equivalents i.e α and β carotenes (Sundram *et al.*, 2003) with its wide range of protective properties against disease and aging as well as being modulators for cellular processes / functions where photooxidative processes predominate by acting as scavengers of oxygen and peroxyl radicals (Van Rooyen *et al.*, 2008). Sebinova and co-workers (1991) documented the increased protection derived from a combination of tocopherol and tocotrienol and further revealed that tocotrienol offers a more efficient protection than tocopherol as it is preferentially consumed by ROS. It has been shown that fresh RPO has no adverse effect on body weight and morphology of body tissues. It also lowers the level of serum lipids and inhibits tumour growth (Kritchevsky, 2000), enhances intestinal uptake of protein and the metabolism of sulphur-amino acids and promotes reproductive capacity (Ebong *et al.*, 1999). Calcium, phosphorous, iron, riboflavin, chlorophyll, xanthophylls, flavonoids and phospholipids and equal proportion of saturated and unsaturated fatty acids have also been identified as part of its constituents (Sundram *et al.*, 2003).

A number of human feeding studies reported that palm oil diets show a reduction of blood cholesterol values ranging from 7%-38% (Mattson and Grundy, 1985; Bonanome and Grundy, 1988). A comparative study in young Australian adults showed that the total blood cholesterol, triglycerides and HDL-cholesterol levels of those fed on palm oil (palm olein) and olive oil were lower than those fed on the usual Australian diet (Choudhury *et al*., 1995). A double-blind cross-over study (Sundram, 1997) showed that a palm olein rich oil diet is identical to an oleic-acid rich diet.

A study on fifty-one Pakistani adults showed that those given palm oil rich diets performed better than those on sunflower oil. Palm oil was found to increase HDL-cholesterol and Apo A-1 levels (Farooq *et al*, 1996). A group in Beijing, China compared the effects of palm oil, soybean oil, peanut oil and lard (Zhang *et al,* 1997a; Zhang *et al*, 1997b) and reported that palm oil caused a significant increase in the HDL-cholesterol as well as a significant reduction in LDL-triglycerides.

Sundram and co-workers (1992) performed a dietary intervention study on a free-living Dutch population who normally consumes diets high in fats. Using a double blind crossover study design consisting of two periods of six weeks of feeding, the normal fat intake of a group of 40 male volunteers was replaced by 70% palm oil. The palm oil diet did not raise serum total cholesterol and LDL-cholesterol, and caused a significant increase in the HDLcholesterol as well as a significant reduction in LDL-triglycerides.

The effects of palm olein and of canola oil on plasma lipids were examined in double blind experiments in healthy Australian adults (Truswell *et al*, 1992). Palm oil performed better than canola oil in raising the HDL-cholesterol (Truswell *et al*, 1992). Other studies have demonstrated that RPO supplementation has beneficial or neutral effects on serum total cholesterol (Zhang *et al.*, 1997a).

A cross-over feeding study showed that the blood cholesterol, triglycerides, HDL-cholesterol and LDL-cholesterol levels of palm olein and olive oil diets were comparable (Ng *et al.,* 1992). A Malaysian study (Ng *et al.*, 1991) was conducted to compare the effects of a diet containing palm oil (olein), corn oil and coconut oil on serum cholesterol. Coconut oil was found to raise serum total cholesterol by more than 10% whereas both the corn and palm oil diets reduced the total cholesterol; the corn oil diet reduced the total cholesterol by 36% and palm oil by 19%. A similar cholesterol-lowering effect of palm oil was observed in 110 students in a study conducted in Malaysia (Marzuki *et al.*, 1991). The study compared the effect of palm oil with that of soybean oil. Volunteers fed on palm oil (olein) and soybean oil for five weeks, with a six-week wash-out period, showed comparable blood cholesterol levels. However, the blood triglycerides were increased by 28% in those on the soybean oil diet.

and aging as well as being modulators for cellular processes / functions where photooxidative processes predominate by acting as scavengers of oxygen and peroxyl radicals (Van Rooyen *et al.*, 2008). Sebinova and co-workers (1991) documented the increased protection derived from a combination of tocopherol and tocotrienol and further revealed that tocotrienol offers a more efficient protection than tocopherol as it is preferentially consumed by ROS. It has been shown that fresh RPO has no adverse effect on body weight and morphology of body tissues. It also lowers the level of serum lipids and inhibits tumour growth (Kritchevsky, 2000), enhances intestinal uptake of protein and the metabolism of sulphur-amino acids and promotes reproductive capacity (Ebong *et al.*, 1999). Calcium, phosphorous, iron, riboflavin, chlorophyll, xanthophylls, flavonoids and phospholipids and equal proportion of saturated and unsaturated fatty acids have also been identified as part

A number of human feeding studies reported that palm oil diets show a reduction of blood cholesterol values ranging from 7%-38% (Mattson and Grundy, 1985; Bonanome and Grundy, 1988). A comparative study in young Australian adults showed that the total blood cholesterol, triglycerides and HDL-cholesterol levels of those fed on palm oil (palm olein) and olive oil were lower than those fed on the usual Australian diet (Choudhury *et al*., 1995). A double-blind cross-over study (Sundram, 1997) showed that a palm olein rich oil diet is

A study on fifty-one Pakistani adults showed that those given palm oil rich diets performed better than those on sunflower oil. Palm oil was found to increase HDL-cholesterol and Apo A-1 levels (Farooq *et al*, 1996). A group in Beijing, China compared the effects of palm oil, soybean oil, peanut oil and lard (Zhang *et al,* 1997a; Zhang *et al*, 1997b) and reported that palm oil caused a significant increase in the HDL-cholesterol as well as a significant

Sundram and co-workers (1992) performed a dietary intervention study on a free-living Dutch population who normally consumes diets high in fats. Using a double blind crossover study design consisting of two periods of six weeks of feeding, the normal fat intake of a group of 40 male volunteers was replaced by 70% palm oil. The palm oil diet did not raise serum total cholesterol and LDL-cholesterol, and caused a significant increase in the HDL-

The effects of palm olein and of canola oil on plasma lipids were examined in double blind experiments in healthy Australian adults (Truswell *et al*, 1992). Palm oil performed better than canola oil in raising the HDL-cholesterol (Truswell *et al*, 1992). Other studies have demonstrated that RPO supplementation has beneficial or neutral effects on serum total

A cross-over feeding study showed that the blood cholesterol, triglycerides, HDL-cholesterol and LDL-cholesterol levels of palm olein and olive oil diets were comparable (Ng *et al.,* 1992). A Malaysian study (Ng *et al.*, 1991) was conducted to compare the effects of a diet containing palm oil (olein), corn oil and coconut oil on serum cholesterol. Coconut oil was found to raise serum total cholesterol by more than 10% whereas both the corn and palm oil diets reduced the total cholesterol; the corn oil diet reduced the total cholesterol by 36% and palm oil by 19%. A similar cholesterol-lowering effect of palm oil was observed in 110 students in a study conducted in Malaysia (Marzuki *et al.*, 1991). The study compared the effect of palm oil with that of soybean oil. Volunteers fed on palm oil (olein) and soybean oil for five weeks, with a six-week wash-out period, showed comparable blood cholesterol levels. However, the blood

cholesterol as well as a significant reduction in LDL-triglycerides.

triglycerides were increased by 28% in those on the soybean oil diet.

of its constituents (Sundram *et al.*, 2003).

identical to an oleic-acid rich diet.

reduction in LDL-triglycerides.

cholesterol (Zhang *et al.*, 1997a).

Thus, the impact of palm oil on serum lipids is more like that of a mono-unsaturated rather than saturated oil. There appears to be several explanations: (1) Palm oil is made up of 50% unsaturated fats and the saturated fatty acids present are palmitic (90%) and stearic (10%). Stearic acid as well as palmitic acid do not raise blood cholesterol levels in people whose blood cholesterol levels are in the normal range (Hayes, 1993; Hayes *et al*., 1995; Hayes *et al*., 1991, Khosla and Hayes, 1994; Khosla and Hayes, 1992). (2) The vitamin E, particularly the tocotrienol present in palm oil can suppress the synthesis of cholesterol in the liver (Qureshi *et al.*, 1991a; Qureshi *et al*, 1991b; Qureshi *et al*, 1980; Mcltosh *et al*, 1991). (3) The position of the saturated and unsaturated fatty acid chains in a triglyceride backbone of the palm oil molecule determines whether the fat will elevate the cholesterol level in the blood (Kritchevsky, 1988; Kritchevsky, 1996). In palm oil, 87% of the unsaturated fatty acid chains are found in position 2 of the carbon atom of the triglyceride backbone molecule (Ong & Goh, 2002). This could explain why palm oil is not cholesterol-elevating. (4) It has an anticlotting effect and prevents the formation of thrombi in the blood vessels. Hornstra (1988) in the Netherlands first demonstrated that palm oil has an anti-clotting effect, and is as antithrombotic as the highly unsaturated sunflower seed oil. A human study (Kooyenga *et al.,*  1997) showed that tocotrienol (from palm oil) supplementation can reduce stenosis of patients with carotid atherosclerosis.

Holub *et al*, (1989) reported that the vitamin E in palm oil inhibits platelets from "sticking" to each other. Other supporting evidence showed that a palm oil diet increases the production of a hormone, prostacyclin that prevents blood-clotting or decreases the formation of a blood-clotting hormone, thromboxane (Sundram *et al*., 1990; Ng *et al*., 1992).

Kurfeld *et al*. (1990) in the United states, using a rabbit model, compared the effects of palm oil with hydrogenated coconut oil, cottonseed oil, hydrogenated cottonseed oil, and an American fat blend containing a mixture of butterfat, tallow, lard, shortening, salad oil, peanut oil and corn oil. At the end of a 14-month feeding period, coconut oil fed rabbits showed the most atherosclerotic lesions, while palm oil-fed rabbits showed less lesions compared to the coconut oil fed rabbits.

More than 70% of the vitamin A intake in Third World countries comes from fruits and vegetables in the form of carotenoids (Van Rooyen *et al.,* 2008). In humans and animals, carotenoids, an important constituent of palm oil, play an important role in protection against photo-oxidative processes by acting as oxygen and peroxyl radical scavengers. Their synergistic action with other antioxidants makes them an even more potent compound.

It has been suggested that different individual compounds exhibiting a variety of antioxidant activities may provide additional protection against oxidative stress when ingested simultaneously (Esterbauer *et al*., 1991). A combination of lipophilic anti-oxidants present in red palm oil results in an inhibition of lipid peroxidation which is significantly greater than the sum of the individual effects (Zhang *et al.*, 1995). This suggests that a cocktail of antioxidants may have a far more profound anti-oxidative effect due to the synergistic action of the individual compounds (Zhang *et al.,* 1995).

The antioxidant properties of RPO has been attributed to the synergistic actions of carotenoids and vitamin E in the presence of lycopene in a natural food environment and this might provide the ultimate dietary supplement to fight disease associated with oxidative stress (Van Rooyen *et al.*, 2008).

Conclusively, it could be said that oxidative stress plays a role in inflammatory and chronic diseases such as HIV/AIDS and TB and contribute significantly to depletion of immune factors, micronutrients and also promotes the progression of disease. Red palm oil could potentially retard the process due to its unique characteristics and also as it is known to be rich in several important antioxidants.

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