Palm oil, palm kernel oil, palm olein and palm stearin are all different products of the palm tree.
Palm oil is extracted from the pulp of the fruit of the oil palm. Palm kernel oil, on the other hand, is extracted from the seed of the oil palm. While red palm oil (also known as crude palm oil) is easily distinguishable by its deep orange to red color, refined palm oil and palm kernel oil can be hard to tell apart. Both are white to yellowish in color and solid at room temperature.
Palm oil contains about 45 g saturated, 40 g monounsaturated, and 8 g polyunsaturated fatty acids per 100 g. Though not as saturated as coconut oil, palm oil is still at the top of the list when it comes to saturation. Palm kernel oil is even more saturated, containing more than 80% saturated fatty acids.
It's no surprise that palm oil has been labeled an unhealthy fat by most health experts. Obviously, this much saturated fat must send cholesterol levels through the roof and, as a result, cause heart disease. Right?
Well, not quite. After going through pubmed for all the abstracts (and a couple of full papers) on palm oil and cholesterol, it's clear that the case is everything but clear. The heart disease part deserves it's own post, but for now let's concentrate on how palm oil really affects cholesterol levels.
Palm oil and cholesterol in animals
In one study, partially refined, bleached and deodorized (RBD) palm oil was fed to rats on different diets (link). All groups that were given palm oil as part of their diet had significantly lower total cholesterol (TC) levels than the control group. In addition, when normal and hyperlipidemic rats were given palm oil, they had higher HDL levels than hyperlipidemic rats that were not fed palm oil. Similar results were seen in another study where rats given palm oil had a higher ratio of HDL to total cholesterol and lower triglycerides than the control rats (link).
An earlier study that fed rats with various fats for a year came to a different conclusion (link). TC was higher in rats fed palm oil than in rats fed with other fats such as sunflower oil or butter. Triglycerides were higher in palm oil and butter groups than in sunflower oil groups. And, to make things even more confusing, rats fed palm oil for four weeks showed a tendency for slightly lower triglycerides and HDL, whereas sunflower oil tended to increase triglycerides and HDL (link).
Basically what the above studies show is that the results vary greatly. Sometimes palm oil improves TC/HDL ratio, sometimes it worsens it. Sometimes triglycerides decrease, sometimes they increase. What's more, these two don't even have to go hand in hand, which makes it hard to decide whether the overall effect is good or bad.
One question that raises at this point is whether refining the oil makes a difference. One study that compared unrefined (that is, red/crude) and refined palm oil found that rats fed unrefined palm oil had lower total cholesterol, LDL, VLDL and higher HDL than those fed refined palm oil (link). Perhaps the tocotrienols in red palm oil play a role? Maybe so, but there is also one study that did not see a difference in cholesterol levels between rats fed red palm oil and refined palm oil for three months (link).
There are also other variables that might affect the end results. For example, I found one rat study that directly compared the effects of fresh and once or repeatedly heated palm oil (link). The rats that were given either fresh or once-heated palm oil did not have any deleterious effect, whereas palm oil heated five times increased total cholesterol and thiobarbituric acid reactive substances (TBARS) levels. This means that even though palm oil tolerates heat much better than most oils, using the same oil many times may not be a good idea.
Similarly, comparing fresh and oxidized (either through heating or prolonged exposure to air) palm oil shows that while both increase total cholesterol compared to rats eating a normal diet, oxidized palm oil increases it even more, and that this is due to an increase in LDL, not HDL (link). Further, oxidized palm oil increased the mean arterial blood pressure of the rats, while fresh palm oil did not.
Unlike humans, hamsters fed oil and dietary cholesterol quickly develop hyperlipidemia. Hamsters that were given various palm oils had dramatically lower levels of total cholesterol, LDL and VLDL than hamsters given coconut oil (link). The three forms of palm oil were red palm oil, refined palm oil and refined palm oil with red palm oil extract. In the hamsters that were fed red palm oil or refined palm oil with red palm oil extract, HDL levels were significantly higher and triglycerides significantly lower than in hamsters fed coconut oil.
The best one of the three was unrefined red palm oil, but as you can see, even refined palm oil had favourable effects. Note also that adding an extract of red palm oil into the refined palm oil improved things, which supports the idea that the carotenoids, tocotrienols and tocopherols play a role in the health effects of red palm oil.
In another study, hamsters given palm oil had higher levels of total cholesterol, HDL and triglycerides than those given olive oil or maize oil (link). The title of the paper suggests that the amount saturated fat is directly responsible for HDL levels in hamsters: when they eat little saturated fat, HDL is low, and vice versa. However, in the previous study HDL increased after switching from coconut oil to red palm oil, even though coconut oil is higher in saturated fat.
In vervet monkeys, palm olein oil reduced the risk the risk for developing early atherosclerotic lesions while not significantly affecting cholesterol levels compared to monkeys given lard or sunflower oil (link). Note, however, that palm olein oil is not the same as palm oil. Although it has a high palmitic acid content like palm oil, palm olein oil is the refined, liquid fraction of palm oil. The solid fraction is palm stearin. Palm olein is about 45% saturated and 55% unsaturated, while palm stearin is 60% saturated and 40% unsaturated. While they may have different effects, at least in rats palm stearin, palm olein and palm oil all increased HDL in one study (link).
Palm oil and cholesterol in humans
While animal studies may give us an idea of what to expect, we are not rats, hamsters or monkeys. Humans are adapted to a different kind of diet through evolution, and cholesterol studies in animals can be pretty misleading when applied to humans.
First, let's take a look at what happens when you give palm oil to people with what doctors would call hypercholesterolemia or high cholesterol. In women with high cholesterol, soybean oil, rice bran oil and palm oil all reduced LDL and TC, despite their differing fatty acid composition (link). Thus, saturated fat does not necessarily increase LDL.
In this study, only soybean oil reduced HDL. Soybean oil also reduced small dense LDL (sd-LDL), while palm oil consumption increased it. That same LDL was more susceptible to oxidation in those who consumed soybean oil, however. Since oxidized LDL appears to be the best predictor of atherosclerosis, perhaps an increased number of small LDL particles with less oxidation is better than increased oxidation with less particles.
When older women with high cholesterol were given sunflower oil (which is very high in PUFA) or palm olein, the latter increased TC and LDL, especially in women with high TC to begin with (link). Contrast this with the previous study where the palm oil normalized cholesterol levels. Still, no difference was seen in TC/HDL ratio. HDL increased only in those with normal cholesterol levels. Again, palm olein also decreased LDL oxidation, especially in those with high cholesterol.
There's also a study that compared sunflower oil and palm olein in older women but with normal cholesterol. This time, the diet containing palm olein increased TC and HDL compared to a sunflower oil diet (link). Another study found palm oil and sunflower oil to cause no difference in HDL, whereas palm oil increased TC and LDL (link). A third comparison of the two oils found the same (link).
Perhaps palm oil and palm olein have different effects on cholesterol? That sounds plausible, but one study found no difference between palm oil, palm olein, palm stearin and soybean oil in terms of LDL, HDL and triglycerides (link). Then again, not all palm oleins are equal. When red palm olein and palm olein was compared with sunflower oil in patients with excessive fibrinogen (a blood clotting factor) in their blood, red palm olein came out on top (link). Palm olein increased TC more than red palm olein and sunflower oil. LDL increased in the palm olein group compared to the sunflower oil group.
So far, we've looked at palm oil vs. PUFA-rich oils, but what about other fats? Lard has a pretty similar fatty acid profile as palm oil. It has plenty of MUFAs and SFAs but only little PUFAs. Comparing palm oil with soybean oil, peanut oil and lard in Chinese adults showed that palm oil reduced TC and LDL, while lard increased both (link). Peanut oil had no effect. Palm oil also improved the TC/HDL ratio.
A study that fed palm oil, lard or puff-pastry margarine to obese women found no difference in cholesterol levels (link). It did find that obese women had lower HDL levels and higher fasting leptin (four times as high!) than normal-weight women, however. So, compared to lard, palm oil either reduces LDL or does nothing.
Peanut oil is 49% MUFA, 33% PUFA and only 18% SFA. The MUFA content is similar to palm oil but its PUFA content is much higher. One study found no difference between palm olein from red palm oil and peanut oil (link). Olive oil is even higher than peanut oil in MUFA, containing about 70% of its fatty acids in the monounsaturated form. One study found no difference between palm olein containing tocotrienols and olive oil in terms of cholesterol (link).
Coconut oil is much higher in saturated fat than palm oil. Unsurprisingly, it tends to raise cholesterol in most animal studies more than other fats. In humans, small amounts may not make a big difference. Enriching the diets of healthy, young women with palm oil or coconut oil did not result in differences in total cholesterol compared to consuming the same amount of energy MUFAs (link). In larger amounts the difference start to become clearer. Compared to coconut oil, palm oil generally results in lower total cholesterol, LDL and HDL (link).
Still, even high amounts of red palm oil doesn't necessarily increase cholesterol. In Chinese men, a diet containing 28% fat with red palm oil accounting for 60% of that, no change was seen in total cholesterol, triglycerides, or HDL after 42 days (link). Plasma concentrations of carotenoids and vitamin E increased, however.
Hydrogenation, which turns liquid fats solid, may also play a role. Compared to saturated fatty acids such as palmitic acid, hydrogenated fats containing trans fatty acids tend to increase total cholesterol and LDL while lowering HDL levels (link, link). One paper compared the effects of palm oil with partially hydrogenated fat and oils high in MUFAs or PUFAs (link). Partially hydrogenated soybean oil and palm oil resulted in higher LDL than regular soybean oil. There was no significant difference in TC/HDL between the oils, but HDL3 was higher after palm oil.
In another study, three different margarines were given to 27 young women (link). One of the margarines was based on palm oil, one on partially hydrogenated soybean oil and one was made with a high content of PUFAs. The PUFA margarine lowered total cholesterol and LDL compared to the other two, while soybean margarine lowered HDL compared to the other two. One study compared the effects of partially hydrogenated soybean oil, high oleic palm olein and unhydrogenated palm stearin (link). Both soybean oil and palm stearin increased TC/HDL compared to palm olein, with palm stearin having a lesser effect than soybean oil.
Looking at the question from the opposite angle gives similar answers. The saturated fat in a typical Dutch diet comes mainly from animal fats and hydrogenated oils. Replacing them with palm oil resulted in an 11% increase in HDL and a 8% decrease in the LDL/HDL ratio (link). Triglycerides were also reduced.
In many of the studies, the subjects are either given supplements or they just basically scoop up the fat with a spoon. This is not how most people actually use these oils, however – they cook with them. When you put different oils into a frying pan and then eat them is when you start to see different results.
For example, using palm oil or soybean oil for cooking does not seem to change serum cholesterol levels much in the short term (link). However, cooking in soybean oil resulted in a 47% increase in triglycerides compared to palm oil, which goes to show that oils high in PUFAs are not very suitable for cooking. Also, some of the effects may only become visible after a longer period of time. There aren't many long-term studies in humans, but Mauritius is an exception. In 1987, the government changed the formula of the commonly used cooking oil from palm oil to soybean oil. As a result, total cholesterol levels dropped by about 0.8 mmol/L in the course of five years (link). There's no mention of triglycerides, unfortunately.
Finally, men and women seem to respond differently to dietary fats. When a small amount of red palm oil was given to healthy subjects for two weeks, all lipid fractions decreased, with a statistically significant decrease seen in LDL and triglycerides (link). A closer look revealed that there was a difference between men and women, however: in men, LDL actually increased mildly.
One study looked at the effects of palm oil in the context of high and low dietary cholesterol (link). Diets high in palm oil slightly increased total cholesterol and LDL with no significant changes in HDL or triglycerides. Interestingly, diets low or moderate in palm oil increased total cholesterol and LDL much more than the diets high in palm oil, even when the high-palm oil group consumed more eggs.
Tocotrienols are generally considered to have a cholesterol-lowering effect (link). The effects of tocotrienol supplements on cholesterol are not conistent, however (link, link). A possible explanation is that alpha-tocopherol might attenuate some of the cholesterol-lowering effect of tocotrienols (link).
Medium-chain triacylglycerods (MCTs) are usually thought to have a neutral effect on cholesterol, but a comparison of MCTs with palm oil and high oleic acid sunflower oil showed that MCT and palm oil had a similar effect (link). Sunflower oil resulted in lower total cholesterol. The authors conclude that "this study suggests that medium-chain fatty acids have one-half the potency that palmitic acid has at raising total and LDL-cholesterol concentrations."
Summary
So what do we make of all this? As I'm sure you noticed, there's a lot of different kinds of studies and a lot of conflicting data out there when it comes to palm oil and cholesterol. Some common themes appear in the results, however:
- Compared to PUFA-rich oils, palm oil increases TC in most human studies
- Compared to MUFA-rich oils, palm oil behaves neutrally in most human studies
- Compared to SFA-rich oils, palm oil reduces TC in most human studies
- In animals, palm oil tends to increase HDL and lower triglycerides
- In humans, palm oil tends to increase LDL, at least in men
- Palm oil makes LDL less susceptible to oxidation
- Small amounts of palm oil don't make much of a difference either way
- Palm oil tolerates cooking well, but don't use the same oil more than once
- Red palm oil seems to have a more neutral effect than refined palm oil
Just from a cholesterol perspective, palm oil doesn't look all that bad – and we haven't even looked at how palm oil consumption affects cardiac risk! Although some conflicting evidence exists, in most of the studies the effect on cholesterol is closely related to the fatty acid composition of the oil.
Thus, when you compare palm oil with sunflower oil, you're most likely going to see an increase in total cholesterol, since polyunsaturated fatty acids tend to lower cholesterol compared to saturated fatty acids. Monounsaturated seem neutral in most cases. Still, keep in mind that individual fatty acids behave slightly differently. The high palmitic acid content of palm oil may explain why HDL levels are unchanged in many human studies.
One thing to remember is that if you use the oils straight from the bottle (e.g. on top of a salad), the difference between sunflower oil and palm oil may not be that great. However, if you use them for cooking, picking an oil high in PUFAs is asking for trouble. Saturated fats such as palm oil are less susceptible to oxidation and also make (the possibly increased) LDL less susceptible to oxidation.
Finally, while refined palm oil is most likely a better choice for cooking than less saturated fats, go for red palm oil whenever you can. Not all studies have shown a significant difference in cholesterol levels between red palm oil and refined palm oil, but some have, and tocotrienols have plenty of other health benefits as well.
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