Dr Michael Mosley (Trust Me, I’m a Doctor) instigated a trial to determine the impact of coconut oil on cardio-vascular health.
94 participants were randomly assigned to one of three groups. They were asked to consume an additional 50g of fat – either coconut oil, butter or olive oil, daily for a period of four weeks. 1
The main measure was the change in total cholesterol.
Below is Mosley’s conclusion.
Note that the emphasis is on the amount of change rather than the more important absolute values.
Below are selected results at the start and the end of the four-week trial.
|Baseline values||Coconut oil|
|Total cholesterol (mmol/L)||5.9||5.9||6.0|
|Systolic blood pressure (mm Hg)||131.4||136.5||133.1|
Selected results at the end of the four-week trial are listed below.
|Results at 4 weeks||Change from baseline||Average Difference
(1st value – 2nd value)
|Systolic blood pressure|
- Adding 50g of fat to a diet an already high-fat diet is not a healthy dietary modification.
- All diets were 36-37% fat (by energy) which is higher than the US average of 33%.
- The average total cholesterol for all diets at the start of the trial was 5.9-6.0 – which is very high. The cholesterol was high at the start of the trial and was still very high at the end. Optimal values are less than 4.0 mmol/L.
- The average LDL cholesterol for all diets at the start of the trial was 3.5-3.7 – which is very high. The LDL cholesterol was high at the start of the trial and was still very high at the end. Optimal values are less than 1.8 mmol/L.
- Total cholesterol was raised substantially for butter (mean 5.9). Coconut oil raised cholesterol somewhat less (mean 0.22). The average increase for olive oil was much less (mean 0.03).
- The baseline values for fasting glucose was 5.3-5.4 mmol/L. A reasonable desirable level is 3.9-5.0 mmol/L. After 4 weeks, the fasting glucose decreased an average of 0.05 mmol/L for coconut oil and 0.06 mmol/L for olive oil. It was raised 0.02 mmol/L for butter. These changes are not significant beneficial outcomes.
- Systolic blood pressure is also high. Optimal systolic blood pressure is less than 120. Coconut oil had a greater tendency to raise the systolic blood pressure compared to butter and olive oil.
- Not all authorities agree that HDL cholesterol is a valid indicator of cardio-vascular health. The fact that coconut oil raised HDL cholesterol is not relevant to better health outcomes. 3 4
A change in cholesterol is not the only impact that a high-fat diet and high saturated fat diet has on health. High-fat diets have a multitude of adverse health outcomes.
A single high-fat meal has a significant impact on endothelial function which takes several hours to recover – just in time for your next high-fat meal. This impacts arterial elasticity and blood flow 5 as well as increasing inflammation. 6
The fluidity of the cell membranes is decreased and the permeability is increased with an increase of saturated fats, as well as increasing the viscosity of the blood and increasing the adhesiveness of blood cells. Having blood components sticking together and sticking to blood arteries is not conducive to good health.
The conclusion of this paper stated, “these findings do not alter current dietary recommendations to reduce saturated fat intake in general but highlight the need for further elucidation of the more nuanced relationships between different dietary fats and health.”
Given the lack of any health benefits in the three diets examined, it is difficult to conclude that a “more nuanced” approach will result in a better understanding of the relationships between dietary fats and health.
A number of researchers studied the relationship of saturated fat to serum cholesterol during the 1950s. J Groen, LW Kinsell, EH Ahrens, A Keys, JM Beveridge and B Bronte-Stewart replaced saturated fats in the diet with polyunsaturated fats. All other components of the diet remained the same and the total fat content of the diet did not change.
When the unsaturated fats, such as corn or safflower oil, were replaced by the saturated fats of butter, lard, or coconut oil, the serum cholesterol rose. The serum cholesterol fell when the polyunsaturated fats were reintroduced. The experiments were repeated, and whilst there was variability with the amount of change for different individuals, the results were consistent for each individual. The changes occurred rapidly within one or two weeks.
Unfortunately, Dr Michael Mosley (Trust Me, I’m a Doctor) used the results of this study to conclude that “coconut oil may be good for you”.
- Khaw, K.-T. et al. (2018) Randomised trial of coconut oil, olive oil or butter on blood lipids and other cardiovascular risk factors in healthy men and women. BMJ Open. 8 (e020167), 15.
- Noone, Y. (2018) Why Dr Michael Mosley now thinks that coconut oil may be good for you [online]. Available from: https://www.sbs.com.au/food/health/article/2018/02/26/why-dr-michael-mosley-now-thinks-coconut-oil-may-be-good-you.
- Roberts, W. C. (2010) It’s the cholesterol, stupid! American Journal of Cardiology. 106 (9), 57–73.
- März, W. et al. (2017) HDL cholesterol: reappraisal of its clinical relevance. Clinical Research in Cardiology. 106 (9), 663–675.
- Vogel, R. A. et al. (1997) Effect of a Single High-Fat Meal on Endothelial Function in Healthy Subjects. American Journal of Cardiology. 79 (3), 350–354.
- Esposito, K. et al. (2007) Effect of a single high-fat meal on endothelial function in patients with the metabolic syndrome: role of tumor necrosis factor-α. Nutrition, metabolism and cardiovascular diseases. 17 (4), 274–279.
- Jakulj, F. et al. (2007) A high-fat meal increases cardiovascular reactivity to psychological stress in healthy young adults. The Journal of Nutrition. 137 (4), 935–939.