Watermelon seeds yield 55% oil on a dry weight basis, and mainly contain linoleic acid (50—60%), followed by oleic acid (15%), and considerably lesser amounts of palmitic and stearic acids (Logaraj, 2010). Hence, watermelon seeds offer about 600 calories and 79% of the recommended daily allowance (RDA) of fat. The major composition of the seed oil is u-6 unsaturated fatty acids, mainly linoleic acid, which helps in decreasing the levels of cholesterol and high blood pressure.
Linoleic acid and a-linolenic acid in moderate concentrations promote good health, but in excess can be harmful. They are involved in energy production, oxygen transfer to blood, hemoglobin synthesis, cell division, growth, and neural functions which is why they are abundant in brain and nervous tissues. Fat deficiency causes chronobiological dysregulation, impaired cognitive sensory responses, and liability to infection, especially in infancy.
In the human body the information traffic is controlled by the nervous, endocrine, and immune systems through electrical and chemical signals either generated or received, which, after modification, activate tissues, muscles, and organs. These three systems therefore involve PUFAs in changing neuronal membrane fluidity, and releasing specific factors, hormones, and cytokines (Yehuda et al., 2000).
The lack of interconversion of u-6 to u-3 fatty acids is compensated for by retroconversions in mammals, as in DHA to AA (Sprecher et al., 1995). Contrarily, plants synthesize these precursor PUFAs (LA, ALA), which are abundant in chloroplastic membranes and certain vegetable oils. Hence, the tissues of phytophagous animals, fish, and shellfish are rich with these precursors, while greens and baked beans have a low content (Sinclair, 1993).
The essentiality of LA for growth and reproduction was proved by the resultant scaly-skinned feet and tail, and retarded growth, in rats deprived of u-6 FAs. The deficient rats mated unsuccessfully, and if fetuses did form they were reabsorbed, or the offspring were born deformed, with histologically abnormal liver and kidneys.
The relative constancy of AA (u-6) and DHA (u-3) levels in brain and central nervous system is essential to maintain the brain phospholipid content, which is reduced by prolonged starvation of u-6 and u-3 FAs over two generations.
Atopic dermatitis is controlled through steroidal anti-inflammatory drug administration by inhibiting the LA cascade, which can also be achieved by clinical administration of high levels of u-3 and decreased LA intake, which act synergistically (Kato et al., 2000). Apart from ADHD (attention deficit hyperactivity disorder), certain brain pathological conditions could also be caused by increased LA intake and elevated u-6 and u-3 ratios in dietary fats and oils (Yoshida et al., 1998).
Although SFAs and MUFAs suppress cholesterol synthesis, u-6 PUFAs (LA and AA) do so to a greater extent (Pischon et al., 2003).While u-3 fatty acids directly reduce cholesterol levels, u-6 fatty acids redistribute them, and the preferred ratio for w-6:w-3 is 1:4 (Yoshida et al., 1993). Cholesterol synthesis is stimulated in the order of S, M > LA > ALA > EPA, DHA, and AA. The first three possibly elevate the isoprenyl intermediate, suppressing the formation of vasodilatory NO, and expedite atherogenesis through prenylation of the oncogene products (Ras, Rho) leading to cell multiplication.
Overdose effects and prevention of atherosclerosis and related diseases
Although as early as 1982 (MRFITRG) high-LA vegetable oil was recommended to prevent atherosclerosis, hypercholesterolemia, etc., it was found to reduce blood cholesterol only transiently (Okuyama et al., 2000) and to be unable to control a type-A behavior pattern (TABP) heart attack. Thus it was not cholesterol, but high levels of LA and high w-6:w-3 PUFA ratios that were the causes of TABP attacks (Okuyama et al., 2000).
There is no general agreement among scientists over the optimal w-6:w-3 ratio, which currently ranges from 4.5 to 2; the only common opinion is that the prevailing ratio of w-6:w-3 must be brought down; it is recommended that both PUFAs (LA and ALA) and HUFAs (AA, EPA, and DHA) should be almost in equal amounts, and the total free energy must be reduced to < 25%. Though LA and u-3 FAs are essential, LA should be < 1%.
In conclusion, people with different food habits consume different dosages of essential fatty acids. The EFAs LA and ALA are necessary for healthy living. Regarding watermelon seed oil, its PUFA values are such that it can be recommended and used as a nutraceutical to alter day-to-day cooking oils to give variable EFA proportions to achieve maximum health benefits. A watermelon seed oil emulsion with u-6 PUFA (LA) can also be used as an effective nutraceutical delivery system for controlled and effective health strategies (Logaraj et al., 2008).
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