In recent years, coconut oil the main product from coconut palm tree [1] has gained wider attention. Many health professionals and other authorities have endorsed the use of coconut oil as a cooking medium in substitution to other vegetable oils and as a supplementary ingredient [1,2]. Scientific and lay literature both promotes the consumption of coconut oil based on assumptions that it has many health benefits. These postulated benefits include cholesterol-lowering, reduction of the risk of cardiovascular diseases, weight loss, improvement of cognitive functions, irritable bowel syndrome, thyroid conditions and diabetes, enhancing the immune system, and promoting wound healing [[3], [4], [5]]. Coconut oil has several unique characteristics that may be responsible for these health benefits. Coconut oil contains nearly 50% of medium-chain fatty acids (MCFA), which are believed to be converted to ketone bodies [6] that pass through the blood-brain barrier and provide energy for glucose depleted brain [7], with a possible therapeutic role in neurodegenerative diseases like Alzheimer’s and Parkinson’s diseases [8]. Moreover, MCFA oxidized efficiently, deposited less in adipose tissue, and increase diet-induced thermogenesis and energy expenditure than long-chain fatty acids (LCFA) [9]. Furthermore, MCFA has fewer calories per gram compared to polyunsaturated fatty acid (PUFA), suggesting beneficial effects on weight loss. Other than MCFA; polyphenols, antioxidants, vitamin E, sterols, and phospholipids contained in coconut oil are also attributed to the various postulated health effects [10].
Although numerous health benefits have been documented, the highest-quality evidence from SRs and SR with MA on the effect on coconut oil and cardio-metabolic parameters shows a negative impact on health [11,12]. Moreover, there are no strong physiological explanations of some mechanisms for the health benefits of coconut oil. For example, claims relating to coconut oil for the treatment of Alzheimer’s disease are based on supplementing caprylic acid (C8) and capric acid (C10) which results in increased plasma ketone body concentrations leading to positive cognitive performance [13,14]. However, in reality, C8 and C10 account for only 10% of the total fat derived from coconut oil [6]. Therefore, it is very unlikely to get a similar effect derived from supplementing medium-chain triglycerides (MCT) (C8, C10) by using coconut oil alone. Moreover, coconut oil has been described for its benefit on weight loss due to its high MCT content. However, lauric acid is the major fatty acid encountered in coconut oil, and although it is considered as a MCFA based on biochemical properties [15], it has also been classified as either MCFA or LCFA in terms of digestion and metabolism [16]. Therefore, the fact that coconut oil aids in weight loss is still debatable because lauric acid does not behave similarly to other MCT. Furthermore, various biological effects of coconut oil, such as blood pressure and cholesterol-lowering, and potential as an Alzheimer’s treatment have also been attributed to its phenolic content and antioxidant potential [[17], [18], [19]]. Nonetheless, phenols are not considered as an antioxidant by the Food and Drug Administration agency, since although it has antioxidant activity in-vitro, similar effects are unlikely to be observed in-vivo [20,21].
The bulk of the evidence often used to back the health benefits of coconut oil is mostly based on observational studies with inferior methodology. The beneficial effect of coconut oil on health is exciting but not well explained. At the same time, most of the beneficial properties of coconut oil have been derived by animal studies or small isolated clinical trials. Therefore, the examination of prevailing reviews on coconut oil consumption and the scientific evidence behind its health utility is important. Systemic review (SR) and meta-analysis (MA) of international studies are considered as the highest level evidence for clinical decisions. Therefore, we aimed to summarize all high-quality evidence arising from SR and MA on coconut oil in this review.
