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Corn oil better for cholesterol than coconut oil

Recently coconut oil has been touted as the new "miracle food," with its proponents claiming that it improves cholesterol scores, induces weight loss, prevents Alzheimer's, and even treats asthma. Unfortunately, many of the studies used to support these claims were performed on rats, mice, or rabbits - not humans.

Its positive effects are thought to be because coconut oil is higher in medium-chain triglycerides than other oils, but the fact remains that it is high in saturated fats (about 85% of its fats are saturated). While those saturated fats from plants are not as bad for you as saturated fats from animal sources, they're still a concern - polyunsaturated and monounsaturated fats are known to be much better for you. In fact, a review of 8 clinical trials and 13 observational studies in humans concluded that there was "no evidence that consumption of coconut oil should be viewed differently from consumption of other sources of SFAs [saturated fatty acids]."

The gold standard of research, of course, is the randomized controlled trial. A team of researchers affiliated with the independent research institution, Midwest Biomedical Research, designed a randomized crossover feeding study (J Nutr 2018;148:1556-1563) that compared the effects of corn oil and coconut oil on LDL cholesterol scores, glucose scores, and levels of c-reactive proteins (a measure of inflammation).

Twenty-three men and women completed the study. To participate, the participants were required to have an LDL cholesterol score between 115 and 190 mg/L and a total fasting glucose score of 375 or less at the start of the study. They could not be diabetic, have diagnosed cardiovascular disease, uncontrolled high blood pressure, or any other chronic disease (including cancer) and their weight had to have remained relatively stable for the 3 months prior to the trial's start. Women were asked to commit to using birth control to avoid pregnancy and all participants were asked to avoid trying to lose weight or even to use any nonsteroidal anti-inflammatory medications except low-dose aspirin.

The study lasted for a total of 11 weeks: an initial 4-week test period, followed by 3 weeks of a "washout" period, then an additional 4-week test period. During each 4-week test period the participants consumed 4 study products (muffins or rolls) per day, replacing other foods in their diet with those products so that their weight remained constant. The difference between the two study periods? During one study period the products were made with corn oil; during the other the products were made with coconut oil. Half the participants were assigned to one type of product and half to the other during the initial study period; for the second study period they switched products.

Cholesterol scores and glucose tolerance tests were performed at the initial screening as well as at the start of each trial period and at multiple points during the trial periods. Body weight, blood pressures, and heart rate were also recorded with each test. Participants kept logs of their consumption of the study foods and also kept a detailed food diary for 3 days (2 weekday, 1 weekend day) during the first and last week of each study period.

So what happened?

The authors note that there were "no [clinically] significant differences" seen in the changes consuming the test products made to body weight or blood pressures. Regardless of whether they were consuming the products made with corn oil or coconut oil, in both cases the subjects gained weight: about 0.6 kilograms while consuming the products containing corn oil, while gaining only about 0.2 kilograms while consuming the products containing coconut oil.

That said, when consuming coconut oil the participants' LDL cholesterol (the bad cholesterol) rose by 4.6%, while when they consumed corn oil their LDL cholesterol dropped by 2.7%. Similarly, total cholesterol rose by 7.1% for those consuming coconut oil products while those consuming corn oil products saw their total cholesterol drop just a little: 0.5%. HDL cholesterol (the good cholesterol) rose slightly more in those consuming coconut oil (by 6.5%) than in those consuming corn oil (5.4%).

What this means for you

Yes, coconut oil improved HDL (good) cholesterol scores more than corn oil did, yet it also raised LDL (bad) cholesterol while corn oil reduced it. It's important to look at more than one score for the effects of a particular food, food group, or even dietary pattern: on the whole, which choice confers the most benefit on the whole?

The authors note in their discussion of this research that "with regard to lipoprotein lipid (LDL) effects, coconut oil is not an optimal choice." I would agree that on the whole your best oil choices are still olive oil and canola oil, with corn oil and other oils high in polyunsaturated oils following after. Oils that are high in saturated fats, like coconut oil, are best used sparingly.

First posted: October 17, 2018