If we’re going to figure out if vegetable oils are healthy, we first need to look at what they’re made of.
Then, we need to decide how those components affect health.
And finally, we need to quantify each one.
At a high level, vegetable oils are pretty much all fat. The the fat in vegetable oil varies by fatty acid content in various oils.
Fats are class of macronutrient, much like protein and carbohydrate. But just like protein can be broken down into separate amino acids and carbs can be broken down into sugars and fibers and starches, fat can be broken down into fatty acids.
Fatty acids come in different shapes and sizes, but are often categorized by their chain length and their degree of saturation.
Note for those that are curious - saturated molecules contain only single bonds between carbon atoms, while unsaturated organic molecules contain at least one double or triple bond (monounsaturated) or more than one (polyunsaturated).
This difference in fatty acid content is what gives rise to the terms saturated fats, monounsaturated fats, polyunsaturated fats, and trans fats.
So first, let’s take a look at the breakdown of fat in 13 vegetable oils.
You’ll notice that coconut oil is high in saturated fats, olive oil, canola oil, and safflower oil are high in monounsaturated fats, and flaxseed oil and grapeseed oil are high in polyunsaturated fats.
Each of these classes can be further subdivided by chain length and bond position. For example, the image on the left is palmitic acid (a saturated fatty acid), and on the right is linoleic acid (a polyunsaturated acid). Notice the double bonds in linoleic acid at points 9 and 12.
Unsurprisingly, these different molecules affect your health in different ways.
Most research has focused on how fat in vegetable oil effects heart health. Specifically, through their modulation of cholesterol.
But it’s not as simple as whether cholesterol is going up or down.
Cholesterol too can be divided into different classes. Generally, cholesterol can be classified into high density lipoproteins (HDL) and low density lipoproteins (LDL).
And like they say, it’s generally good to keep high high and low low.
What has been shown to be good predictor of cardiovascular disease (CVD), then, isn’t simply whether a fatty acid raises total cholesterol.
It’s important to know how each fatty acid affects both HDL and LDL.
Therefore, the ratio between these two is a much better predictor of CVD risk and overall cholesterol change or each individually.
For example, lauric acid is a saturated fat that significantly raises LDL (the bad kind). But, it also significantly increases HDL too. Thus, the HDL/LDL ratio actually has been shown to tip the scales in a more positive direction for heart protection.
This is one reason why saturated fats can cause quite a bit of controversy in the nutrition world.
Let’s see how each vegetable oil is broken down by major fatty acids. Note: another interactive chart.
Another reason has to do with calorie replacement.
We can only eat so much food. Assuming we aim to keep our calorie consumption under control, if we decide to eat more fats, we have to eat less of something else (specifically, proteins or carbohydrates).
This relative scale is a common way nutrition researchers measure the relative health of different nutrients.
So when researchers debate the merits of different fatty acids, they are often measured relative to something else.
Replacing carbohydrates with fats can improve your CVD risk profile, but it depends on the mix of fats.
Saturated fats tend to make little to no change. Some fatty acids raise your total serum cholesterol to HDL ratio, others lower it. Some, don’t change it much at all.
Thus, depending on the ratio of saturated fatty acids, CVD risk tends to shift either way but not by much.
But replacing carbohydrates with unsaturated fats - like monounsaturated fats and polyunsaturated fats - routinely shows an improved CVD risk profile evidenced by an improved total cholesterol to HDL ratio, epidemiological studies, and controlled clinical trials.
Taking all of this into account, the chart below shows the relative improvement to CVD risk for each vegetable oil when it is used to replace carbs. Note, that each one is positive! That means, each oil improves your heart health when it replaces carbs in an isocaloric fashion (calorie for calorie).
Coconut oil helps the least - roughly 86% of the fat content is saturated fat.
And vegetable oils high in polyunsaturated fats, like flaxseed oil, produce even better results.
But what about other things in oils, like vitamins and minerals?
If we want to look at overall health of a food product, we should take into account everything in it, including vitamins and minerals.
Vegetable oils are a great source of vitamins E and K.
Vitamin E helps prevent oxidative damage to cell membranes, and vitamin K helps with the formation of blood clotting factors and bone proteins.
So much like plumbing or city infrastructure, these uncharismatic vitamins don’t often steal the limelight but are fundamental for a healthy body.
And some oils have trace amounts of choline, zinc, iron, calcium, or potassium, but they are present in extremely low amounts that don’t add up to much.
But vitamins E and K are present in many oils in large enough amounts to meet your daily recommended allowances! See how they compare to each other, below.
Note: Many of us don’t meet the recommended amounts for these vitamins, so these are great sources for our nutritional health. Click here to view our interactive charts to see average micronutrient consumption for each vitamin and mineral broken down by age and gender.
See how the vitamin content of vegetable oils compare, below.
We’ve mostly described the good parts of vegetable oils. But there are a few things to consider to avoid negative health effects, too.
Each cooking oil has a slightly different smoke point - the temperature at which it begins to combust and produce smoke. This is important for two reasons.
First, it helps dictate your cooking needs. Along with different flavors, you can use different oils if you want to cook or saute foods at high temperatures that require a different oil.
Second, it is important for considering something called polycyclic aromatic hydrocarbons, or PAHs.
PAHs come in many varieties, but many of these chemicals are toxic and/or carcinogenic. You definitely don’t want to overdo it on these guys.
The CONTAM panel of the European Food and Safety Agency (EFSA) reported on the concentration levels in common foods - including oils - and any changes that occur from various processing and cooking methods.
Their analysis “indicated low concern for consumer health at the average estimated dietary exposures.” But those who consume very large amounts may approach threshold levels of safety.
Note: seafood and animal meats also contained similar, and sometimes higher, amounts of PAHs.
And where does the smoke point come into play?
If vegetable oils get heated to their smoke point, PAHs get volatilized into the smoke and can concentrated in the foods that are cooked in them.
In fact, a similar issue arises when grilling meats. But only under certain circumstances. For instance, according to the EFSA report, meats cooked on a charcoal grill (without a flame) saw PAH levels rise only when fat from the meat dripped down onto the coals and volatilized into smoke below the meat itself.
Fortunately, frying or sauteing foods on a stove top rarely gets to the smoke point of cooking oils. Cooking temperatures are usually around 250 °F.
With the exception of flaxseed oil and safflower oil, you won’t usually reach the smoke point. Unless of course you need really hot temperatures.
At the end of the day, the boring but sage nutrition advice is to consume any vegetable oils - like any food for that matter - in moderation and as part of a balanced diet.
With respect to your heart health, changes to HDL and LDL cholesterol levels suggest that vegetable oils across the board improve your CVD risk profile when compared to carbohydrates.
However, oils higher in unsaturated fats produce a more significant improvement to cholesterol levels than do saturated fats.
And cholesterol isn’t the only worry about saturated fats. Other research has identified other possible biochemical mechanisms for poor health linked to saturated fats - like the stiffening of organelle membrane walls and ensuing functional impairment.
Thus, as part of a balanced diet approach, the American Heart Association recommends keeping saturated fats to approximately 5-6% of total caloric intake.
But don’t forget about their vitamin contributions too. Factoring those in (and using some math to adjust their quality score), the top five oils for health are canola oil, soybean oil, sunflower oil, safflower oil, and olive oil, while sesame oil, palm oil, and coconut oil round out the bottom.
Of course, we still have much to learn. Complications exist, like the foods we consume these oils with and our individual genetic and environmental differences that affect nutrition absorption and metabolism.
But this should be a good start!
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