October 2016 Issue
By Judith C. Thalheimer, RD, LDN
Vol. 18, No. 10, P. 32
What's behind its "health halo," and does the latest science back it up?
According to a 2016 survey published in The New York Times, 72% of Americans think coconut oil is healthful. Only 37% of nutrition experts surveyed agree.1 While some believe coconut oil is a "superfood" that can do everything from controlling dandruff to curing Alzheimer's disease, most experts say it's a dangerous saturated fat to be avoided. This huge discrepancy is due in part to the nature of the fatty acids in this enigmatic tropical oil.
Most of the health benefits attributed to coconut oil are associated with its high content of medium-chain fatty acids (MCFAs). Fatty acids are carbon chains classified by how long they are and how many double bonds they have. While not all sources agree, MCFAs, which always are saturated, typically are defined as having six to 12 carbons. Long-chain fatty acids (LCFAs) have more than 12 carbons and can be saturated or unsaturated.2 The two behave very differently in the body. "Short- and medium-chain fatty acids are more easily absorbed than long-chain fatty acids because they're more water soluble," says Marie-Pierre St-Onge, PhD, FAHA, an associate professor of nutritional medicine at Columbia University Medical Center in New York City. "Also, they can be absorbed directly into the portal circulation and transported straight to the liver for rapid oxidation. Long-chain fatty acids, on the other hand, need to be broken up and packaged in chylomicrons," lipoprotein particles that transport fat around the body. St-Onge explains that the chylomicrons travel through the peripheral circulation to the liver. On the way, fat can be deposited around the body. The rapid absorption and oxidation of MCFAs make them a unique form of dietary fat.
Many dietitians are familiar with MCFAs because they make up medium-chain triglyceride (MCT) oil, a manufactured fat generally made by processing coconut or palm kernel oils in a laboratory.3 Since they're more easily absorbed, MCTs are sometimes used as a fat source in total parenteral nutrition and for treatment of fat absorption disorders such as cystic fibrosis, celiac disease, Crohn's disease, pancreatitis, and malabsorption in newborns.3 MCT oil is also popular with athletes as an energy source, as MCFAs are efficiently converted into fuel.4
Is Coconut Oil MCT Oil?
While the fatty acids in the much-studied MCT oil all have eight or 10 carbons (C8 and C10), most of the MCFAs in coconut oil have 12 (C12).5 "C12 is a controversial fatty acid," St-Onge says. "Some consider it an MCFA, and some don't. Do these 12-carbon chains behave more like eight- or 10-carbon chains in the body, or more like the longer 14- or 16-carbon chains?" Most likely they're somewhere in the middle. While some sources say the majority of C12 (known as lauric acid) is transported directly to the liver and rapidly oxidized, others report that only as little as 25% to 30% follow this route, as opposed to 95% of the C8 and C10 MCFAs that constitute MCT oil.2,5 Since coconut oil is 47% C12 and only around 16% C8/C10, it isn't equivalent to MCT oil and can't be assumed to have the same health benefits identified in research on MCTs.5
Following are some of the most common claims about coconut oil and a summary of what the research says.
Coconut oil promotes weight loss.
Coconut oil is slightly lower in calories than other fats—8.3 kcal per gram for MCTs vs 9 kcal per gram for long-chain triglycerides (LCTs). But at 115 kcal per tablespoon, using lots of coconut oil isn't a good way to cut calories.3,6
A more interesting argument for coconut oil over other oils in a weight loss plan is that energy expenditure is greater with the metabolism of MCFAs than LCFAs.7 "MCFAs go straight to the liver, where they are elongated to make immune factors, prostaglandins, and other longer-chain fatty acids," St-Onge says. "This is not an efficient process, so it burns more calories. They also bypass peripheral tissues, so MCFAs are less likely to be deposited in peripheral tissue. In animal studies, rats being fed MCTs have less fat mass than those fed LCTs." Short-term feeding studies in humans have shown that MCTs increase fat oxidation and thermogenesis compared with LCTs.8 There also are reports of greater satiety, suggesting lower food intake when LCTs are replaced with MCTs in the diet.3
But the MCT oil used in nearly all the available research is composed entirely of C8 and C10 fatty acids. "While it's true that coconut oil is the largest food source of MCTs, only about 15% are C8 or C10," St-Onge says. "The rest are C12, which has not been proven to have the same effect. You would have to eat a massive amount of coconut oil to get the percentage of C8 and C10 MCTs shown to help with weight loss."
A 2009 study in humans comparing the effect of coconut oil and soybean oil on abdominal obesity in women found that while both groups lost the same modest amount of weight, the coconut oil group had a decrease in waist circumference, whereas the soybean oil group had an increase.9 While this study is promising, St-Onge cautions that it wasn't well controlled.
The bottom line: While high-quality studies in humans are lacking, replacing LCTs in the diet with MCTs may be modestly helpful in supporting weight loss. However, the MCTs in coconut oil are not the same as those most commonly studied for weight loss and may not necessarily have the same effect. There's no solid evidence at this time to recommend coconut oil as a weight loss aid.
Coconut oil reduces cardiovascular disease (CVD) risk.
Since coconut oil is 92% saturated fat, a discussion of coconut oil and CVD runs right into the current disagreement over the role of saturated fats in heart disease. While a subset of researchers firmly believe that saturated fats aren't associated with heart disease and stroke, all major policy-making organizations in the United States still recommend limiting saturated fat intake to reduce CVD risk. "Saturated fats are solid at room temperature," St-Onge says, "so they make cell membranes less fluid. Unsaturated fats, which are liquid at room temperature, make membranes more flexible, which is more desirable." The lauric acid (C12) in coconut oil does have a lower melting point than longer-chain saturated fats, and may therefore impart less rigidity. It also could potentially have different effects on cholesterol and/or lipid metabolism in the liver, but there's currently no conclusive proof that coconut oil consistently acts differently from other saturated fats.5
Societies in which coconut products make up a large part of the traditional diet have been observed to have less CVD, but these diets also are typically high in heart-healthy foods like vegetables and fish and low in processed foods. It's considered unlikely that adding coconut oil to the typical Western diet would in-and-of-itself lower CVD risk.5
Coconut oil does appear to have a positive impact on at least one heart-health metric: Epidemiologic studies have found an association among consumption of coconut products like whole coconut, coconut cream, and coconut oil and higher levels of HDL cholesterol.5 But a 2016 review of literature on coconut consumption and CVD in humans found that coconut consumption also might raise LDL cholesterol, total cholesterol, and serum triglycerides—all CVD risk factors.5 Results of clinical studies have been inconsistent.5 "When lauric acid replaces carbohydrates in the diet, HDL goes up, but experts aren't exactly sure what an increase in HDL means in terms of cardiovascular health," says Penny Kris-Etherton, PhD, RD, FAHA, FNLA, CLS, a professor in the department of nutritional sciences at Pennsylvania State University. "Plus, the fact that it also raises LDL cholesterol is not good. Besides, there are good data showing there are other fats that are better for heart health." In other words, while some studies show that lauric acid (C12) may reduce the total cholesterol to HDL ratio and LDL to HDL ratio compared with carbohydrates, it isn't the most heart-healthy choice compared with other fats.10 "One thing we do know is that when a person replaces saturated fatty acids in their diet with mono- and polyunsaturated, the risk of heart disease goes down," says Libby Mills, MS, RDN, LDN, FAND, a spokesperson for the Academy of Nutrition and Dietetics.
The bottom line: While coconut oil seems to raise HDL levels, research is inconclusive as to whether it improves the total cholesterol to HDL ratio, a more important predictor of CVD risk. In addition, coconut oil is 92% saturated fat, which the majority of experts agree should be consumed in limited amounts. "There are a lot of studies out there, but simply no robust proof that coconut oil is good for your heart health," Kris-Etherton says. Data are strong in demonstrating that mono- and polyunsaturated fatty acids are better choices.
Coconut oil can prevent and treat diabetes.
In a 1992 study, lauric acid (C12), the primary fatty acid in coconut oil, increased insulin secretion in mouse islet cells.11 This study has been extrapolated to conclude that coconut oil will improve insulin secretion in humans. A literature search turned up no human studies on the effect of coconut oil on insulin sensitivity or diabetes, and those studies looking at MCFAs are inconclusive. It's important to note that, in the mouse study mentioned above, linoleic acid (a C18 polyunsaturated essential fatty acid) had the same effect on insulin secretion as lauric acid.11
High dietary intake of saturated fat is known to impair insulin sensitivity and lipid metabolism.12 But in a 2009 study, insulin sensitivity was reduced by 30% in rats fed a diet high in saturated LCFAs, while the insulin sensitivity of those fed MCFAs wasn't affected, raising the possibility that MCFAs aren't as detrimental to insulin sensitivity as other saturated fats.12 A 2011 study on mice in the Journal of Nutritional Biochemistry, however, concluded that both LCFAs and MCFAs increased insulin resistance, but via different mechanisms.13 Human studies are lacking.
The bottom line: While there's a possibility that MCFAs (including lauric acid) may behave differently in the body than longer-chain saturated fats, there's no direct evidence that coconut oil increases insulin sensitivity or can be helpful in the prevention or treatment of diabetes in humans. The American Diabetes Association considers coconut oil a saturated fat to be limited.14
Coconut oil can reverse Alzheimer's disease.
Some research suggests that ketones may be helpful in the treatment of neurological disorders. In Alzheimer's disease, brain cells can lose their ability to use glucose for fuel. The theory is that ketones could serve as alternative fuel sources for these brain cells. Ketones are byproducts of the breakdown of fats by the liver, particularly the breakdown of MCTs. While there's some research showing that ketone-producing diets may help treat epilepsy and other neurological disorders, most of the literature is theoretical and preliminary, and very little has been done in humans. And none of the research used coconut oil.15 A Phase II study conducted in 2009 on a product providing high doses of C8 found some minor improvements in patients with mild to moderate Alzheimer's. The company chose not to proceed with larger clinical trials, but is marketing the product as a "medical food" instead.6,15
The bottom line: According to the Alzheimer's Association, there have been a few anecdotal reports of coconut oil helping with Alzheimer's, but there's never been any clinical testing, and there's no scientific evidence suggesting that it helps.6 The same is true of over-the-counter MCT oils.15
Coconut Oil in the Diet
While currently there isn't any proof that coconut oil is a miracle food, "coconut oil does have a place in our food system," Mills says. "It adds value to certain cuisines. For example, if you're making a Thai dish, using coconut oil as a base adds a delightful coconutty taste. That being said, it shouldn't be used to excess." Mills also cautions against high-heat cooking. "Heat damages oils across the board," she says. "At temperatures above the smoke point, the fat is breaking down and free radicals are forming, which in turn can damage cell walls, causing inflammation that can be an underlying factor in cardiovascular disease. Damage to cell walls also is associated with cancer. The smoke point of coconut oil is 50 degrees lower than that of extra-virgin olive oil, so there will be less degradation if you use olive oil."
While research on MCTs raises some intriguing possibilities for their widening role in health and wellness, the research that exists at this time can't be directly applied to coconut oil. Science is simply unclear on how the primary MCFA in coconut oil, lauric acid (C12), behaves in the body. And, while coconut oil does have some of the better-studied C8 and C10 MCFAs, clients would have to eat plenty of coconut oil to reach levels thought to be effective. To answer clients' questions about coconut oil and other trendy fats, nutrition professionals must understand how fatty acids differ from each other and how these differences impact their behavior in the body. By being wary of weak studies overblown in media hype, and by recognizing that studies on MCT oil (C8/C10) can't be generalized to coconut oil, dietitians and other health professionals can help ensure clients make the best choices for their health goals. Still, there's much to discover about coconut oil and fats in general. Keep an eye on emerging research; while no food is truly a miracle food, coconut oil may have something to teach us yet.
— Judith C. Thalheimer, RD, LDN, is a freelance nutrition writer, a community educator, and the principal of JTRD Nutrition Education Services.
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11. Garfinkel M, Lee S, Opara EC, Akwari OE. Insulinotropic potency of lauric acid: a metabolic rationale for medium chain fatty acids (MCF) in TPN formulation. J Surg Res. 1992;52(4):328-333.
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13. De Vogel-van den Bosch J, van den Berg SA, Bijland S, et al. High-fat diets rich in medium- versus long-chain fatty acids induce distinct patterns of tissue specific insulin resistance. J Nutr Biochem. 2011;22(4):366-371.
14. Fats. American Diabetes Association website. http://www.diabetes.org/food-and-fitness/food/what-can-i-eat/making-healthy-food-choices/fats-and-diabetes.html. Updated August 13, 2015. Accessed July 23, 2016.
15. Can coconut oil treat Alzheimer's? Berkeley Wellness website. http://www.berkeleywellness.com/healthy-mind/memory/article/can-coconut-oil-treat-alzheimers. Published June 1, 2012. Accessed August 1, 2016.