Coconut oil has oozed into mainstream nutrition lately and established itself as a seemingly miraculous health food. Proponents sing its praises and seem to hold it in god-like esteem. But do these claims hold up to the rigors of scientific research? Furthermore, what are the health effects of consuming coconut oil, good and bad? Let’s find out.
First, some background on coconut oil. Coconut oil is about 92% saturated fat. However, unlike most of the fat we consume, which is in long chain forms, coconut oil is composed mostly of medium chain triglycerides. This has given rise to the idea that coconut oil has unique, beneficial effects of health compared to the others fats in our diet.
Among the many health claims applied to coconut oil is its purported ability to help with weight loss. A number of studies have been published exploring the weight loss inducing effects of medium chain triglycerides (1,2,3,4,5,6,7,8,9,10) and such studies provide some compelling evidence that MCT’s may increase weight loss in animal and human studies, yet these results can’t be easily extrapolated to coconut oil. While coconut oil does contain a large amount of medium chain triglycerides, the primary fatty acid in coconut oil is lauric acid, which is typically absent from the MCT preparations being tested in these studies. Because of this, any of the effects of such medium chain triglycerides on weight loss should not be cited when discussing the effects of coconut oil on weight loss.
Studies on rats (11,12) have demonstrated that coconut oil produces less weight gain or more weight loss than rats fed an equal amount of a long chain triglyceride rich fat. However, in these studies corn oil and other linoleic acid rich oils were often used as the long chain triglyceride fat source. An alternative hypothesis when looking at these studies is that coconut oil performs well simply by proxy and the linoleic acid rich oil is causing increased weight gain. Studies have been performed in which rats were given diets with either coconut oil, a control diet (typically low in fat), and a linoleic acid rich oil (13,14,15). In such studies, the linoleic acid enriched diet almost always results in more weight gain, while neither the control diet or the coconut oil consistently comes out the winner. This is supportive of the weight gain inducing effects of linoleic acid rich oils, and not supportive of the weight loss inducing effects of coconut oil. However, rats aren’t always the best model for human weight gain or loss (16), so let’s look at how coconut oil affects actual people.
In one study (17) two groups of overweight women were given either 30 milliliters of either soybean oil or coconut oil. They were advised to follow a low calorie diet and walk for 50 minutes everyday. At the end of 12 weeks, both groups had lost weight but only the coconut oil group experienced a decrease in waist circumference, indicating a decrease in abdominal obesity. In 2 separate studies by Peter JH Jones et al., groups of healthy women were given 32 percent of their calories as either butter and coconut oil or beef fat (18,19). In the first study (18), the group eating butter and coconut oil had a higher basal metabolic rate and greater fat oxidation than the beef fat group. The second study (19) essentially ending up with the exact same findings–basal metabolic rate increased, fat oxidation increased, and energy expenditure was higher. However, this study noticed something important: the increase they saw in metabolism started to decrease significantly by the end of the two week trial. This indicates coconut oil’s effect on metabolism eventually goes away and I’ve yet to see a study that refutes this idea.
But just because coconut oil doesn’t increase metabolism in the long run doesn’t mean it isn’t helpful for weight loss in other ways. In one study (20), men were fed either lauric acid (the main fatty acid in coconut oil) or oleic acid (the main fatty acid in olive oil) via a catheter until the participants were no longer hungry. At the end of the three day trial, the men being fed lauric acid reduced their calories more than the oleic acid group. Another study found that men who ingested lauric acid had lower post meal ghrelin levels (21). Ghrelin is hormone that increases appetite and if lauric acid lowers ghrelin levels it might influence us to lower our food intake. Another study fed mice various medium chain triglycerides found in coconut oil and reported that such triglycerides might be used to convert ghrelin into its active form (22). Well that isn’t good, especially since this study found this effect took a while (about 2 weeks) to occur, making it harder to look for in controlled trials. Still, this study is mostly bad news for caprylic acid, a medium chain triglyceride which only comprises about 8 percent of coconut oil. The effect of lauric acid was fairly small. These studies suggest potential mechanisms by which coconut oil might increase or decrease caloric intake, but because they haven’t been adequately studied in humans over a long period of time it would be presumptuous to assume they tell us anything definitive about coconut oil’s effect on weight loss.
Despite coconut oil’s recent reputation as a dieter’s best friend, there are relatively few long term studies examining coconut oil’s effect on weight loss to make definitive claims about it’s potential as a weight loss aid. It does appear to increase metabolic rate for a little while though, so that’s something, but this effect eventually goes away.
In part 2 of this series I’ll examine whether coconut oil increases cholesterol and cardiovascular disease.