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The oil in the coconut

Care should be taken when weighing the dietary benefits of saturated fats.

Question: On his website, Dr Joseph Mercola claims coconut oil has amazing health benefits. Could you throw some light on this? I suspect there is a lot of misinformation out there and that saturated fat, particularly from coconut, is often unfairly maligned.

Answer:

Whereas Dr Mercola's website espouses coconut oil's health benefits, the National Heart Foundation's website recommends reducing coconut-oil intake because of its high saturated-fat content and the consequent cardiovascular health risks. Who should we believe?

The National Heart Foundation is a non-profit, non-governmental organisation that funds research and education to improve New Zealanders' cardio­vascular health; Mercola, an American, is selling coconut oil. Mercola's pro-coconut views must be weighed carefully.

Mercola claims the saturated fats in coconut oil aren't harmful, as they are healthy medium-chain fats (not long-chain saturated fats). He says the medium-chain triglycerides (MCTs) in coconut oil are digested differently and can promote weight loss.

Indeed, MCTs are digested differently, providing rapid energy rather than being stored, making them ideal for clinical applications such as feeding patients with certain metabolic disorders. And yes, a 2008 study published in the American Journal of Clinical Nutrition found MCT oil, as part of a weight-loss plan, was better than olive oil for improving weight loss.

The devil is in the detail, though, as the MCT oil used in the 2008 study comprised fatty acids of eight and 10 carbons in chain length. However, coconut oil contains just 15% of these fatty acids; instead, a 12-carbon fatty acid is the predominant fatty acid in coconut oil (at around 47.5%).

Delve further and we find various definitions for MCTs. Often they're defined as eight to 10 carbons long, other times it's eight to 14 carbons. Either way, Mercola fails to acknowledge that the health benefits he attributes to MCTs don't automatically apply to coconut oil, as coconut oil differs vastly in its overall fatty acid profile from the various MCT oils used in research and clinical applications. Coconut oil must be assessed on its own merits.

Mercola suggests coconut oil isn't harmful and refers to a 1981 study about a Polynesian population, published in the American Journal of Clinical Nutrition. And yes, vascular disease was rare among the Pukapukans and Tokelauans in this study, even though they had high saturated fat intakes because they consumed a lot of coconut.

The Kitavans living on the Trobriand Islands of Papua New Guinea also consume a lot of coconut yet have very low stroke and ischaemic heart disease rates. However, we must consider each study population's overall dietary pattern and lifestyle, says Alex Chisholm, a senior lecturer in human nutrition at the University of Otago. Chisholm's research focuses on how varying dietary components affects the risk of cardiovascular disease.

The Pukapukan, Tokelauan and Kitavan diets all differ greatly from those of Westerners. Tubers, fruit, fish and coconut were dietary staples for the Kitavans, for example; hence their total dietary fat and sodium intake was low by Western standards, and their soluble fibre, mineral and vitamin intake was higher. Plus, their high fish intake contributed heart- healthy omega-3 fats.

In Sri Lanka coconut intake added significant quantities of saturated fat to the traditional diet, too, but unlike the Polynesian and Melanesian populations, in Sri Lanka the incidence of coronary heart disease is relatively high. A 2001 study, published in the British Journal of Nutrition, found replacing coconut fat in the Sri Lankan diet with a mixture of soybean and sesame oils (mainly unsaturated fatty acids) improved total LDL and HDL (low- and high-density lipoprotein) cholesterol levels - changes expected to lower cardiovascular disease risk.

We can never assume research findings from one population group apply elsewhere, as Mercola has done. Eating a small amount of coconut occasionally isn't going to do harm if the rest of your diet is healthy.

However, making coconut oil your main dietary source of oil is not a good idea if you want to keep your ­cholesterol in the right ballpark. Chisholm says unsaturated oils are more beneficial.