Tuesday, March 15, 2016

Health Implications of Cooking with Oils


[Health and Medicine]


We hear quite a bit about the health benefits of various types of oils that are used in preparing our foods.  There has been much attention paid to such factors as caloric intake, the content of trans fatty acids, levels of Omega-3 and 6, mono and polyunsaturated fats, and the implication to your overall health in general (including obesity) and cardiovascular health in specific. What is often not discussed is what happens to these oils when used in cooking, and particular, as their smoke point is reached.  This article will attempt to quickly touch on all these points, with greater emphasis placed on the implications of cooking with these oils.

Trans Fats
There are two broad types of trans fats found in foods: naturally-occurring and artificial trans fats. Naturally-occurring trans fats are produced in the gut of some animals and foods made from these animals (e.g., milk and meat products) may contain small quantities of these fats. Artificial trans fats (or trans fatty acids) are created in an industrial process that adds hydrogen to liquid vegetable oils to make them more solid. The primary dietary source of trans fats is partially hydrogenated oils found in processed foods. Look for them in the ingredient list on food packages. In November 2013, the U.S. Food and Drug Administration (FDA) made a preliminary determination that partially hydrogenated oils are no longer Generally Recognized as Safe (GRAS) in human food.

Food Sources
Trans fats are easy to use, inexpensive to produce and last a long time.  Trans fats give foods a desirable taste and texture. Many restaurants and fast-food outlets use trans fats to deep-fry foods because oils with trans fats can be used many times in commercial fryers. Several countries (e.g., Denmark, Switzerland, and Canada) and jurisdictions (California, New York City, Baltimore, and Montgomery County, MD) have reduced or restricted the use of trans fats in food service establishments.

Before 1990, very little was known about how trans fat can harm your health. In the 1990s, research began identifying the adverse health effects of trans fats. Based on these findings, FDA instituted labeling regulations for trans fat and consumption has decreased in the US in recent decades, however, some individuals may consume high levels of trans fats based on their food choices. Trans fats can be found in many foods – including fried foods like donuts, and baked goods including cakes, pie crusts, biscuits, frozen pizza, cookies, crackers, and stick margarine and other spreads.

Concerns
Trans fats raise your bad (LDL) cholesterol levels and lower your good (HDL) cholesterol levels. Eating trans fats increases your risk of developing heart disease and stroke. It’s also associated with a higher risk of developing type 2 diabetes.

Monounsaturated and Polyunsaturated Fat
Monounsaturated and polyunsaturated fats are generally found in plants and are touted as healthy fats, unlike trans fats, saturated fats, and cholesterol. Organizations such as the American Heart Association (AHA) encourage people to switch to foods based on monounsaturated and polyunsaturated fats from those that contain saturated and trans fats, which are generally processed fats or come from animal-based fat sources such as butter or meat products. Food often contains a combination of different types of fats. 

Monounsaturated fats are made up of a chain of carbon with one pair of carbon molecules joined by a double bond. The more double-bonds there are, the more solid the fat will be. Monounsaturated fats are generally liquid at room temperature, but turn slightly solid when chilled. Polyunsaturated fats have two or more double bonds between carbon atoms in the carbon chain backbone of the fat. They are more solid than monounsaturated fats but less so than saturated fats. This makes polyunsaturated fats also liquid at room temperature.

Health Benefits
Both monounsaturated fats and polyunsaturated fats have distinct health benefits. There is evidence that both types of fats reduce LDL cholesterol levels in the blood when included in a diet low in saturated and trans fats, according to the AHA. This helps lower risk of coronary artery disease and stroke. Monounsaturated fats have the added benefit of being high in Vitamin E and in helping to maintain or develop cells in the body. 
         


Essential Fatty Acids
Your body needs two types of polyunsaturated fatty acids -- omega-3s and omega-6s -- from your diet, because your cells cannot make these fatty acids themselves. Both omega-3 and omega-6 fatty acids contribute to brain function. Omega-3 fatty acids also reduce inflammation and lower your risk of cardiovascular disease. 

Food Sources
Monounsaturated fats are found in olive oil, peanut oil, canola oil, avocados, nuts, and seeds. Polyunsaturated fats are found in many vegetable oils, including safflower, corn, sunflower, soy and cottonseed oils, as well as in nuts and seeds. The omega-3 fatty acids can be found in flaxseeds, walnuts and some fatty fish, such as salmon and herring while omega-6 fatty acids found in pecans, Brazil nuts, and sesame oil.

Concerns
While they have shown health benefits, monounsaturated fats and polyunsaturated fats are still fats and should not be consumed overabundance. Like all fats, they have 9 calories per gram. Of these two types of fats, the AHA says evidence has not shown one to be better over the other for health. Fats overall, including these two, should make up less than 25 percent to 35 percent total daily calorie intake, the AHA says.

Some of the most common cooking oils you’ll find in many kitchens are not optimally healthy (e.g., cottonseed, corn, sunflower, peanut and soybean oils). Although you may hear much about the benefits of the polyunsaturated fats found in these oils, their omega-6 fatty acid content is a lot higher than their omega-3 fatty acid levels. This causes an imbalance in the body and a whole host of problems related to inflammation (the body’s natural response to an overload of omega-6) such as cancer, cardiovascular diseases, and other problems.  

Type of oil or fat
Saturated
Mono
Poly
Omega-3
Omega-6
Avocado oil
12%
74%
14%
0.95%
12%
Safflower oil
10%
13%
77%
0
74%
Rice bran oil
20%
47%
33%
1.60%
33%
Mustard oil
13%
60%
21%
5.90%
15%
Tea seed oil
22%
60%
18%
0.70%
22%
Sunflower oil (linoleic, refined)
11%
20%
69%
0%
56%
Olive oil (extra light)
14%
73%
11%
0
0
Soybean oil
15%
24%
61%
6.70%
50%
Corn oil
13%
25%
62%
1.10%
53%
Sesame oil (semi-refined)
14%
43%
43%
0.3
41%
Peanut oil / groundnut oil
18%
49%
33%
0
31%
Palm oil
52%
38%
10%
0.20%
9.10%
Olive oil (refined)
14%
73%
11%
0
0
Sunflower oil (high oleic, refined)[30]
9%
82%
9%
0.20%
3.60%
Almond
8%
66%
26%
0
17%
Cottonseed oil
24%
26%
50%
0.20%
50%
Diacylglycerol (DAG) oil
3.05%
37.95%
59%
0
-
Olive oil (virgin)
14%
73%
11%
0.70%
9.80%
Macadamia oil
12.50%
84%
3.50%
0
2.80%
Walnut oil (Semi-refined)
9%
23%
63%
10%
53%
Canola oil
6%
62%
32%
9.10%
18%
Grapeseed oil
12%
17%
71%
0.10%
69%
Ghee, clarified butter
65%
32%
3%
0
0
Olive oil (extra virgin)
14%
73%
11%
0.70%
9.80%
Coconut oil, (virgin)
92%
6%
2%
0
1.80%
Sesame oil (Unrefined)
14%
43%
43%
0.3
41%
Hemp oil
9%
12%
79%
18%
55%
Margarine, soft
20%
47%
33%
2.40%
23%
Margarine, hard
80%
14%
6%
2%
22%
Butter
66%
30%
4%
0.30%
2.70%
Lard
41%
47%
2%
1%
10%
Pumpkin seed oil
8%
36%
57%
0%
64%
Flaxseed oil (Linseed oil)
11%
21%
68%
53%
13%























.
There are cooking oils with an ideal, balanced ratio of omega-3 to omega-6 fatty acids (butter, lard, coconut and palm oils). People who eat a non-industrial diet have an Omega-6:Omega-3 ratio of about 4:1 to 1:4, most being somewhere in between. The ratio today is 16:1, much higher than what we are genetically adapted to.  This is a key factor in inflammatory based illnesses.

You’ve probably heard that olive oil is a healthy choice to use when cooking, which is absolutely correct but it isn’t your only option (especially when we get into higher temperature; more on that later). Some other oils with healthy omega-3 to omega-6 ratios are coconut, palm and avocado oils. These nutrient-rich oils contain an abundance of healthy fats and antioxidants and have the added bonus of adding great flavor to your food.

Processing
Cooking oil extraction and refinement are separate processes. Extraction first removes the oil, typically from a seed, nut or fruit. Refinement then alters the appearance, texture, taste, smell, or stability of the oil to meet buyer expectations.

Extraction
There are three broad types of oil extraction:
  • Chemical solvent extraction, most commonly using hexane.
  • Pressing, using an expeller press or cold press (pressing at low temperatures to prevent oil heating).
  • Decanter centrifuge. 
In large-scale industrial oil extraction, you will often see some combination of pressing, chemical extraction and/or use of centrifugation in order to extract the maximum amount of oil possible.

Refinement
Cooking oil can either be unrefined or refined using one or more of the following refinement processes (in any combination):
  • Distilling, which heats the oil to evaporate off chemical solvents from the extraction process
  • Degumming, by passing hot water through the oil to precipitate out gums and proteins that are soluble in water but not in oil, then discarding the water along with the impurities
  • Neutralization, or deacidification, which treats the oil with sodium hydroxide or sodium carbonate to pull out free fatty acids, phospholipids, pigments, and waxes
  • Bleaching, which removes "off-colored" components by treatment with fuller's earth (clay material that has the capability to decolorize oil or other liquids without chemical treatment), activated carbon, or activated clays, followed by heating, filtering, then drying to recoup the oil
  • Dewaxing, or winterizing, improves clarity of oils intended for refrigeration by dropping them to low temperatures and removing any solids that form
  • Deodorizing, by treating with high-heat pressurized steam to evaporate less stable compounds that might cause "unusual" odors or tastes
  • Preservative addition, such as BHA and BHT (widely used by the food industry as preservatives, mainly to prevent oils in foods from oxidizing and becoming rancid) to help preserve oils that have been made less stable due to high-temperature processing
  • Filtering, a non-chemical process which physically screens out larger particles, could be considered a step in refinement, although it doesn't alter the state of the oil
Most large-scale commercial cooking oil refinement will involve all of these steps in order to achieve a product that's uniform in taste, smell, and appearance, and has a longer shelf life. Cooking oil intended for the health food market will often be unrefined, which can result in a less stable product but minimizes exposure to high temperatures and chemical processing.

Cooking with Healthy Oils
There is where we get into the complexities by extreme temperatures, as it is not as straightforward as merely selecting a healthy oil. Cooking with healthy oils is great for your body, but it’s important to consider the type of cooking you’ll be doing and how high the temperatures will be getting. Different oils are ideal for different heats, and using the wrong oil can be detrimental to your health if you cook it beyond its smoke point.

What is the Smoke Point?
The smoke point of an oil is exactly what it sounds like: the point at which an oil begins to smoke. The smoke point is a natural property of unrefined oils, reflecting an oil’s chemical composition.   The smoke point for an oil/fat is the temperature at which it stops shimmering and starts sending out some serious smoke signals. Learning how to interpret those signals is a crucial element of any good cook's vocabulary (for flavor, health and safety reasons). Many unrefined oils are packed with minerals, enzymes, and other compounds that don't play well with heat.

To understand how smoke points affect food, we have to look to where our fats come from and how they've been processed. Traditionally, oils are extracted from nuts and seeds through mechanical crushing and pressing. If bottled immediately thereafter, you've got a cold-pressed raw, or "virgin" oil, which tends to retain its natural flavor and color.

Many unrefined oils are packed with minerals, enzymes, and other compounds that don't play well with heat and tend to be especially susceptible to rancidity; these are the oils best-suited to drizzling, dressings, and lower temperature cooking. It follows that one of the main reasons for refining (or processing) an oil is to raise its smoke point. For this discussion, let’s focus on olive oil, a pantry staple commonly used in cooking.

As with all other oils, olive oil’s smoke point varies with how much it’s been processed, so high-quality extra-virgin olive oils have a lower smoke point (around 320°F) than lighter, highly-processed olive oils (which can have a smoke point up to 420°F.)

Generally, olive oil’s smoke point is lower than that of some other oils such as soybean or canola, so it’s not an ideal oil for frying. (For comparison, refined soybean and sunflower oils have some of the highest smoke points, at around 450°F, and avocado oil’s smoke point is 520°F.)

Type of oil or fat
Smoke point
Uses
Avocado oil
271 °C (520 °F)
Frying, sautéing, dipping oil, salad oil
Safflower oil
265 °C (509 °F)
Cooking, salad dressings, margarine
Rice bran oil
254 °C (489 °F)
Cooking, frying, deep frying, salads, dressings. Very clean flavored & palatable.
Mustard oil
254 °C (489 °F)
Cooking, frying, deep frying, salads, dressings. Very clean flavored & palatable.
Tea seed oil
252 °C (486 °F)
Cooking, salad dressings, stir frying, frying, margarine
Sunflower oil (linoleic, refined)
246 °C (475 °F)
Cooking, salad dressings, margarine, shortening
Olive oil (extra light)
242 °C (468 °F)
Sautee, stir frying, frying, deep frying, cooking, salad oils, margarine
Soybean oil
241 °C (466 °F)
Cooking, salad dressings, vegetable oil, margarine, shortening
Corn oil
236 °C (457 °F)
Frying, baking, salad dressings, margarine, shortening
Sesame oil (semi-refined)
232 °C (450 °F)
Cooking, deep frying
Peanut oil / groundnut oil
231 °C (448 °F)
Frying, cooking, salad oils, margarine
Palm oil
230 °C (446 °F)
Cooking, flavoring, vegetable oil, shortening
Olive oil (refined)
225 °C (437 °F)
Sautee, stir frying, deep frying, cooking, salad oils, margarine
Sunflower oil (high oleic, refined)[30]
225 °C (437 °F)
Cooking
Almond
221 °C (430 °F)
Baking, sauces, flavoring
Cottonseed oil
216 °C (421 °F)
Margarine, shortening, salad dressings, commercially fried products
Diacylglycerol (DAG) oil
215 °C (419 °F)
Frying, baking, salad oil
Olive oil (virgin)
215 °C (419 °F)
Cooking, salad oils, margarine
Macadamia oil
210 °C (410 °F)
Cooking, frying, deep frying, salads, dressings. A slightly nutty odor.
Walnut oil (Semi-refined)
204 °C (399 °F)[32]
Salad dressings, added to cold dishes to enhance flavor
Canola oil
204 °C (399 °F)
Frying, baking, salad dressings
Grapeseed oil
204 °C (399 °F)
Cooking, salad dressings, margarine
Ghee, clarified butter
190–250 °C (374–482 °F)
Deep frying, cooking, sautéing, condiment, flavoring
Olive oil (extra virgin)
190 °C (374 °F)
Cooking, salad oils, margarine
Coconut oil, (virgin)
177 °C (351 °F)
Cooking, tropical cuisine, beauty products
Sesame oil (Unrefined)
177 °C (351 °F)
Cooking
Hemp oil
165 °C (329 °F)
Cooking, salad dressings
Margarine, soft
150–160 °C (302–320 °F)
Cooking, baking, condiment
Margarine, hard
150 °C (302 °F)[note 2]
Cooking, baking, condiment
Butter
150 °C (302 °F)
Cooking, baking, condiment, sauces, flavoring
Lard
138–201 °C (280–394 °F)
Baking, frying
Pumpkin seed oil
121 °C (250 °F)
salad oils
Flaxseed oil (Linseed oil)
107 °C (225 °F)[29]
Salad dressings, nutritional supplement


What Happens Past the Smoke Point?

When an oil is heated past its smoke point, it generates toxic fumes and free radicals which are extremely harmful to your body (i.e., even carcinogenic). When the smoke point is reached, you’ll begin to see the gaseous vapors from heating, a marker that the oil has started to decompose.

Decomposition involves chemical changes that not only negatively affect the food’s flavor and nutritional value, but also create cancer-causing compounds that are harmful when consumed and/or inhaled.

So if you’ve cooked your olive oil too long and it starts smoking, please turn off the stove and keep the vapors out of your lungs! And definitely throw away any food that’s been in contact with the oil; it’s much better to start again than to risk putting these free radicals into your body.

So while extra-virgin olive oil is a great choice for health (it’s the least refined and most nutrient-dense), it’s not the best pick if you’ll be working with high heats.

The nutrients in extra-virgin olive oil start to oxidize and degrade starting as low as 300°F. Opt for extra-virgin olive oil in salad dressings, marinades, drizzled over vegetables for roasting or pan-frying and blended with hummus and sauces for a smooth, decadent flavor and tons of health benefits.  If you’ll be cooking over 320°F but still want to reap the health benefits of olive oil, opt for a lighter, more refined type with a higher smoke point to avoid the risks mentioned above.

Cooking with Other Healthy Oils
Unrefined walnut oil is another great pick for it’s monounsaturated fats and other nutritional benefits, but like extra-virgin olive oil, it doesn’t stand up well to heat. Its low smoke point (also 320°F) means it is better used for drizzling on vegetables or using at low temperatures.

Cooking with Coconut Oil
Coconut oil has a higher smoke point, at 350°F, than extra virgin olive oil, so it can be a good choice if you’ll be working with slightly higher heats. However, coconut oil is still best used at low to moderate temperatures, while refined olive oil (non extra-virgin) is the better choice for higher temps.

While coconut oil has received a bad rep in the past for its high saturated fat content, studies have shown that our bodies efficiently use saturated fat for energy. Coconut oil has many other benefits like:
  • Hydrates your skin
  • Curbs sugar cravings
  • Boosts metabolism
  • Eases digestion
  • Supports immunity
It also adds a slightly sweet flavor to food that many people enjoy.

Cooking with Avocado Oil
Avocado oil, with a milder flavor than olive oil, is extremely high in monounsaturated fatty acids and has a very high smoke point at 520°F, making it a great choice for cooking at high temperatures.

Avocado oil is actually even more ideal than vegetable or soybean oil for cooking at high temperatures but its higher cost makes it less popular than its cheaper counterparts. Opt for avocado oil when you can, though, to reap nutritional benefits along with the higher smoke point.

It’s safe to use when pan-frying, baking, grilling and searing meats, and adds a delicious nutty flavor along with plenty of vitamins and cancer-preventing compounds.

Bottom Line
Selecting healthy oils in general begins with an oil that consists of the right types of fats and in the appropriate ratios.  Various additional nutrients and enzymes can have further health and flavor implications but can also lower the smoke point, so you will have to be thoughtful about what sort of cooking you are doing (and the level of heat involved) as part of your oil selection criteria.  Cooking oils that are heated up to and beyond their smoke point create health concerns in not only your food, but even in the air your breath.  So that extra virgin olive oil that is perfect for salad dressings and marinades is probably not the best choice for most stovetop cooking.

Hopefully, this has given you enough information to at least help you become aware, and from there, you would ideally do further research to form your own informed insights and opinions.

1 comment:

  1. Ghee looks like a save choice. Why is the smoke point for many of oils a range of temperatures while others have a distinct temperature? Are you familiar with general health advice from Dr. Bert Herring (www.fast-5.com)?

    ReplyDelete