Coconut Oil and Health Part 2: Cholesterol and Cardiovascular Disease

As I’ve already pointed out, coconut oil is almost entirely saturated fat and for this reason the Food and Drug Administration, World Health Organization, Department of Health and Human Services, American Dietetics Association, and American Heart Association advice against its consumption due to the effect of saturated fats on cholesterol levels. What a buzzkill for coconut lovers. Yet many defenders of coconut oil argue that the majority of saturated fats in coconut oil are of medium chain length, which produces a favorable effect on cardiovascular disease and CVD risk factors. So what are the effect of coconut oil on cholesterol levels? And more importantly, what does the scientific literature suggest about coconut oil and cardiovascular disease? Let’s find out.

Studies on medium chain triglycerides have been done in humans and animals in which MCT’s seem to have produced negative effects on cholesterol levels (1,2). But again, MCT’s are not coconut oil, so these studies aren’t applicable to this discussion.

Epidemiological studies on coconut oil eating populations are interesting. These studies tend to support the idea that coconut oil does not increase rates of cardiovascular disease and possibly cholesterol levels (3,4,5,6), though contradictory studies exist (7). However, many of these studies contain confounders, so let’s scoot on over to controlled animal studies and see how things look.

Studies in rabbits have examined the effect of coconut oil on blood cholesterol and triglycerides, noticing coconut oil produces worse blood lipids than unsaturated fats like olive oil when dietary cholesterol is present in the diet (8,9). Yet when dietary cholesterol is not present in the diet, this increase in cholesterol appears to goes away (10) and no atherosclerosis occurs (10,34). In one study, mice with gene knockouts that increase susceptibility to CVD were used to compare coconut oil and olive oil (11). In the LDL receptor knockout group coconut oil produced less atherosclerosis, while in the ApoE knockout group olive oil came out ahead. In studies on hamsters, red palm oil and olive oil have produced better effects on blood lipids and atherosclerosis than coconut oil (12,13). In a study on rats (14), coconut oil increased cholesterol more than rice bran oil and sesame oil. However, it increased HDL (“good cholesterol”) as well as LDL, so it’s hard to say which group came out ahead. Another study on rats pitted a diet of 15% coconut oil against 15% fish oil (15). The fish oil rats had lower cholesterol and triglycerides, but it wasn’t all sunshine and decreased blood lipids; the fish oil group had lower vitamin E and vitamin A levels, and roughly 3 times more lipid peroxidation. And another study comparing diets of coconut oil and fish oil in rats observed the same effect of fish oils lowering cholesterol and triglycerides (16). However, it was noted that the fish oil group experienced a lowering of HDL and additionally, an increase of lipid build up in the liver.

Interestingly, there appears to be a big difference between virgin coconut oil and refined coconut oil (known as copra oil). In this study (17) virgin coconut oil, copra oil, and sunflower oil were given to rats for 45 days. By the end of the study, the VCO group had better antioxidant status, more oxidant resistant LDL, lower triglycerides, and lower cholesterol than the other two groups. In yet another study on rats, virgin coconut oil increased antioxidant enzymes and prevented lipid peroxidation relative to copra oil and peanut oil in rats (18). Peanut oil produced the worst effects on these health markers.

Finally, one more study in rats (19) found a high coconut oil diet produced a significantly worse lipid profile than rats fed a comparatively low fat diet (well, the coconut oil group lost abdominal fat, but that’s about it). Things to take into consideration with this study is that the lower fat diet had more fiber and starch and the coconut oil group was fed about 30% more sugar. Also, rats aren’t humans and we can only assume so much when looking at rat studies. So let’s move on to the good stuff: human studies.

In a 12 week study on women eating low calorie diets, supplemental coconut oil increased HDL and decreased LDL while supplemental soybean oil produced the opposite effect (20). Score one for the coconut oil, baby. In an older study, men with high cholesterol were given diets with either safflower oil or a mixture of safflower and coconut oil (21). Both groups experienced a roughly equal decrease in cholesterol, but this study was fairly short term. Another old study noted that coconut oil produced higher cholesterol than safflower oil and olive oil, but the study was fairly short term and didn’t measure LDL and HDL (22). In another study, men were fed 20% of their calories as either coconut oil, beef fat, or safflower oil (23). The coconut oil group experienced a greater increase in LDL than the other two. However, the coconut oil group saw their HDL increase, while the other groups did not. As with animals, coconut oil may increase both LDL and HDL cholesterol (24,25), so the effect on CVD are hard to assume. Furthermore, studies that show coconut oil increases cholesterol are often short term and don’t account for the possibility that such an effect is transient, as has been occasionally observed in long term trials in animals:

The y-axis is cholesterol and the x-axis is in months. As this study went on, cholesterol levels in rabbits fed coconut oil returned to baseline. Like nuthin’ ever happened.

When we use the term postprandial we are referring to what is observed after a meal. In a study where women were fed diets with lots of coconut oil or olive oil, the coconut oil group experienced lower postprandial levels of lipoprotein A and tissue plasminogen activator antigen (26). Although postprandial effects are not always reliably extrapolated to the long term, these effects are supportive of coconut oil’s beneficial effects on risk factors of cardiovascular disease (27,28,29). Another study had subjects consuming high fat meals containing either coconut oil or sunflower oil (30). The coconut oil group appeared to experience better flow mediated dilation, but their incubated HDL produced more inflammatory adhesion molecules than the sunflower group when exposed to TNF-alpha. However, it has been pointed out that this study did not account for the vitamin E content of the sunflower oil and thus the practical application of this esoteric testing may in fact be limited (31).

The problem with all these studies is that they measure the effect of coconut oil on cardiovascular disease risk factors, but not cardiovascular disease. Thankfully, I found a study that attempted to do just that. It formed 2 groups, put 100 men in both groups, gave each group 28% of their calories from either equal mixtures of corn and sunflower oil or coconut and peanut oil and published a study at five years (32) and ten years (33). At both intervals no major difference in cholesterol levels were observed between the two groups and, more importantly, no major difference in heart attacks and mortality was observed either. This study would have been stronger had coconut oil alone been used (damn you peanut oil, you confounder!) but it is still interesting.

Finally, lauric acid has repeatedly been shown to improve the ratio of total:HDL cholesterol in humans more than any other fatty acid or carbohydrate period (34). This is important because a major meta analysis of 61 clinical trials found that total:HDL cholesterol ratio is the best predictor of future heart attacks based on blood lipid measurements (much more than LDL alone) (35).

When examining whether coconut oil causes an elevation of cholesterol, the evidence appears mixed. It appears that it does in many studies, but it often concurrently increases HDL cholesterol. And of course this elevation may eventually go away or not happen at all. Coconut oil, especially virgin coconut oil, also appears beneficial to a number of risk factor for cardiovascular disease. To suggest that coconut oil increases heart disease risk is not a statement well supported by evidence. However, the idea that coconut oil is beneficial to to cardiovascular health is also weakly supported, though perhaps stronger, especially when coconut oil replaces certain other vegetable oils in the diet.

In my next and last post on coconut oil I’ll look into the potential health benefits of coconut oil consumption.

References:
1. http://www.ajcn.org/content/79/4/564.full
2. http://www.ajcn.org/content/65/1/41.abstract
3. http://www.ajcn.org/content/34/8/1552.full.pdf
4. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2796.1994.tb00804.x/abstract
5. http://www.ncbi.nlm.nih.gov/pubmed/3519928
6. http://www.ajcn.org/content/22/5/594
7. http://www.ncbi.nlm.nih.gov/pubmed/9316363
8. http://www.sciencedirect.com/science/article/pii/0021915088901426
9. http://circres.ahajournals.org/content/20/6/658.short
10. http://circres.ahajournals.org/content/7/3/448.abstract
34. http://www.ncbi.nlm.nih.gov/pubmed/6057698
11. http://www.ncbi.nlm.nih.gov/pubmed/11606787
12. http://www.sciencedirect.com/science/article/pii/S0955286305000781
13. http://www.ncbi.nlm.nih.gov/pubmed/10673913
14. http://jn.nutrition.org/content/141/1/24.full.pdf
15. http://informahealthcare.com/doi/abs/10.3109/10715769109145779
16. http://jn.nutrition.org/cgi/content/abstract/117/6/1011
17. http://www.sciencedirect.com/science/article/pii/S1751499107000431
18. http://www.sciencedirect.com/science/article/pii/S0308814605006412
19. http://www.jacn.org/content/18/1/36.short
20. http://www.springerlink.com/content/02ngg2413wm2w630/
21. http://www.ajcn.org/content/7/1/30.full.pdf
22. http://www.ajcn.org/content/42/2/190.full.pdf
23. http://agris.fao.org/openagris/search.do?recordID=US9022778
24. http://www.ncbi.nlm.nih.gov/pubmed/14493263
25. http://www.ncbi.nlm.nih.gov/pubmed/14608053
26. http://www.ncbi.nlm.nih.gov/pubmed/14972427
27. http://www.ajcn.org/content/18/4/237.full.pdf
28. http://stroke.ahajournals.org/content/30/1/7.full
29. http://circ.ahajournals.org/content/110/3/292.full
30. http://www.ncbi.nlm.nih.gov/pubmed/16904539?dopt=AbstractPlus
31. http://content.onlinejacc.org/cgi/content/full/49/17/1825
32. http://jama.ama-assn.org/content/202/13/1119.abstract
33. http://www.sciencedirect.com/science/article/pii/S0140673673917364
34. http://www.ncbi.nlm.nih.gov/pubmed/12716665
35. http://www.ncbi.nlm.nih.gov/pubmed/18061058?

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s