Coconut oil has long been a part of the pharmacy inventory. I remember, as a pre-registration student, stocking the packed goods shelves with 40g jars of the oil. In those days it was primarily purchased as a hair conditioner by middle-aged men from the Indian subcontinent. Recently, however, it has been publicised as a healthy form of cooking oil.
Coconut oil is high in saturated fats. However, unlike those found in animal fat, which exist primarily as long chain triglycerides (LCTs) that are stored as fat, coconut oil has an unusually high content of medium chain triglycerides (MCTs), which are more likely to be metabolised and used for energy.
MCTs tend to have a lower calorific content per gram than LCTs, and studies have shown that they enhance thermogenesis, or fat-burning. In addition to these benefits to weight loss, MCTs are metabolised to ketones — the cornerstone of the Atkins-type diets. In a study on rats, where calories were provided by either MCTs or lard, the MCT-fed rats lost significantly more weight, although their calorie consumption was the same. Another study demonstrated 23% less fat deposits in an MCT-fed group, compared to the LCT group, and increased MCT intake has been shown to cause appetite suppression.
Nutritional scientists point out that not all commercially available coconut oils are the same, and the partially hydrogenated form is considered just as harmful as any other highly processed oil containing trans-fats. A second type is known as refined coconut oil, which is extracted from chemically bleached and de-odorised coconut flesh. Only virgin coconut oil is considered unrefined, pressed from the fruit of mature coconuts without the use of chemicals or high temperatures. It is high in antioxidant phenolic compounds and is the form of the oil to which beneficial effects are attributed.
In parts of the world where coconut is a dietary staple, such as certain South Pacific islands, up to 60% of calorific intake comes from coconuts. However, the population enjoys excellent health, and heart disease is almost unknown. Diets high in MCTs have been shown to improve glucose tolerance and to reduce body fat when compared to diets high in LCTs. In a study of two groups, in which 40% of calories were derived from either MCTs or LCTs, the MCT group showed an improvement in insulin-mediated glucose metabolism, which led to the suggestion that coconut oil may improve insulin sensitivity in type II diabetes.
The oil also possesses antimicrobial activity through the 12-carbon lauric acid, which makes up almost half of the fatty acids in coconut oil. Lauric acid is digested to the monoglyceride monolaurin and both lauric acid and monolaurin have been shown to have activity against the pathogens Staphylococcus aureus and Candida albicans.
Despite evidence suggesting that coconut oil may have a positive effect upon cardiovascular health, dietary guidelines still suggest avoiding saturated fats including MCTs. Critics of coconut oil state that studies to date have involved small samples over short periods of time, whereas the body of evidence supporting the health benefits of unsaturated fatty acids is more established. Some studies have also suggested that the beneficial effects of the oil are much reduced when it is heated to temperatures of more than 160 degrees Celsius, which casts some doubt on claims made for its use in cooking.