Fats and Oils… an overview
Knowledge of fats and oils has changed over the years and is sure to change again in the future. The best we can do is to understand what the experts are saying today. Here’s my summary of the latest knowledge, presented as clearly as I am able.
Fats and oils contain different quantitities of more than two dozen fatty acids. They are usually grouped into the following categories:
Polyunsaturated Fats (liquid even when refrigerated)
Effect on cholesterol: Lowers both LDL (”bad”) and HDL (”good”)
Consists of subcategories:
Omega-3 (alpha-linoleic or linolenic)
Relatively rare in nature. Plays a role in regulating blood pressure and blood clotting. High ratios of Omega-3 to Omega-6 have been found to reduce the risk of heart disease. 1 part Omega-3 to 4 parts Omega-6 (1:4 ratio) is considered a fairly high ratio, and that’s what the Japanese consume. North Americans typically consume a ratio of only 1:20 to 1:50! Prior to the industrial revolution, the normal ratio was 1:1. [10]
Primary food sources:
Flax seed oil (55%)
Cold-water fatty fish oils (~25%)
Walnuts
Omega-6 (linoleic)
Polyunsaturated fats consists mostly of Omega-6.
Primary food sources:
All non-tropical vegetable oils
Monounsaturated Fats (liquid at room temperature)
Effect on cholesterol: Lowers LDL and raises HDL (hooray!)
Primary food sources (oleic acid):
Olive oil (75%)
Canola oil (61%)
Nuts (almonds, pecans, cashews, peanuts)
Avocados
A note about Canola
Canola oil looks like the ideal oil: high in good monounsaturated fat, very low in bad saturated fat, cheap, and flavourless. It was invented in Canada by selectively breeding the rapeseed plant. Rapeseed is unfit for human consumption because of a high erucic acid content, but Canola has been bred to contain little or no erucic acid. Note that selective breeding does not mean the plant was genetically modified in the modern sense — it is a relatively natural process of human-controlled evolution, where plants exhibiting desirable characteristics are kept for future generations while those with undesirable characteristics are destroyed. Selective breeding has been used to produce things like seedless grapes and oranges (and the bananas we eat that may be destined for extinction, but we’ll save that for another discussion).
The controversy arises because of a few studies that have shown canola oil to create a deficiency of heart-healthy vitamin E and sometimes to cause heart lesions [7]. And to make things worse, some of the Omega-3 fatty acids in canola oil are converted to trans fatty acids (see below) during the deodorizing process. That being said, canola oil still doesn’t seem like an awful choice to me, but it is somewhat controversial and you’ll have to decide for yourself!
Saturated Fats (solid at room temperature)
Effect on cholesterol: Raises LDL
Primary food sources:
Animal fats and tropical oils, including,
Chicken fat (31%)
Pork fat (40%)
Beef fat (48%)
Palm oil (51%)
Cocoa butter (60%)
Butterfat (68%)
Coconut oil (91%)
To complicate things a bit, some studies [5] have found that one of the saturated fatty acids, stearic acid, does not seem to raise blood cholesterol, possibly because its melting point is above body temperature and it is therefore not easily absorbed. Cocoa butter is 35% stearic acid. Still other sources [6] say that stearic acid may not raise cholesterol but it can play a role in coronary events because it seems to increase the blood’s ability to clot. Studies [5] have found that cocoa butter does not have an adverse effect on blood cholesterol (likely due to its high stearic acid content), and the polyphenols found in cocoa (flavonoids, also found in red wine and green tea) are good antioxidants, meaning they offer benefits in fighting inflammation, and potentially in preventing heart disease and cancer. Does this mean that chocolate is a health food? Not at all, since it is still high in fat and sugar, but it does suggest that a piece of chocolate is probably a better treat than a donut — even a chocolate donut.
There is also some indication that coconut oil and palm kernel oil might not be as bad as they look [8] given their high saturated fat content. They are both extremely high in lauric acid, a major component of mothers’ milk. This is why infant formulas are often high in coconut oil. It’s true that people in the tropics eat lots of coconut oil and have a relatively low incidence of heart disease, but it certainly isn’t clear whether their good health is the result of ingesting coconut oil or of a generally healthier lifestyle (fruits, vegetables, and exercise).
Trans fatty acids
Effect on cholesterol: Raises LDL and possibly lowers HDL
Primary food sources:
Hydrogenated oils (vegetable shortening), found in:
Hard margarine
Many cookies, especially creme filled and wafers
Chocolatey coatings
Many crackers
Cake mixes and icing
Pastry (usually shortening, lard, butter, or a combination)
Pretty much anything that contains fat and has a good shelf life
Fried and fast foods (Harvey’s and New York Fries to a lesser extent)
Most naturally occurring unsaturated fats contain primarily “cis” fatty acids. When a cis fatty acid is heated beyond 160 C (320 F) or hydrogenated, it changes into a “trans” fatty acid. Trans fats also occur in nature as as the result of first-stomach fermentation in ruminants (cows, sheep, goats, etc).
Thus, they can be found in small amounts in meat and dairy products.
Again, in the interest of complicating things, there is one trans fatty acid, conjugated linoleic acid, that occurs naturally and prevents cancer in animals and reduces deposition of body fat (also in animals). It isn’t yet known if these benefits are enjoyed by humans. This is just more evidence of how little we really know about nutrition…
Even though Harvey’s and New York Fries are doing the “better” thing when they fry in sunflower oil instead of vegetable shortening, don’t forget that cis fatty acids start to turn into trans fatty acids when they are heated to frying temperatures! The sad fact is, deep fried food will always bad for you, so eat it in moderation. I like fried stuff as much as anybody, but I’ve learned to eat it only when I know I will really enjoy it. [Homer voice] mmmmm…deep fried meat… 
Trans fats are the most evil of fats, and they are far too prevalent in the standard North American diet. Although nutritionists have been waving their arms about trans fats for a decade or more, companies are only now starting to replace hydrogenated fats with non-hydrogenated oils. Canada and the USA have introduced legislation requiring the declaration of trans fats on nutritional labels within the next couple of years. If you’re looking at a label that doesn’t declare trans fat, you can calculate it by adding up the polyunsaturated, monounsaturated, and saturated fats, then subtracting that number from the total fat. The difference is the hidden trans fat. I’ve been doing that calculation ever since nutritional labelling started, so I’m pretty happy about the new legislation!
Summary
Eat only olive oil and flax seed oil in small amounts. Everything else will kill you! Actually, these will kill you too, only more slowly.
Here’s how I like to break down fats to keep things simple:
Very good for you:
Extra virgin olive oil (preferably unheated)
Expeller-pressed flax seed oil (stored in fridge and unheated)
Pretty good for you:
Tree nuts (all of them, really) and avocados.
Fish oils (fatty cold-water fish)
Neutral:
Vegetable oils other than olive and flax.
Not very good for you:
Animal fats
Dairy fats
Tropical fats
Very bad for you:
Vegetable shortening and hydrogenated oils.
Oils that have been heated beyond 160 C (320 F)
You will find people who would argue about the position of most of the items in that list (this is what keeps nutrition interesting!). However, there are two things that I have never seen anyone dispute:
1. Olive oil is the best fat to use in your daily diet
2. Trans fats (hydrogenated oils) are bad for you and should be avoided
In general, less fat is better. Certainly less fat means fewer calories. However, it’s interesting to note that good cardiac health and low rates of cancer can be found in the populations of Spain, Greece, and Italy, where 50 percent of dietary intake comes from fat, specifically cold-pressed extra-virgin olive oil. In northern Canada, the Inuit traditionally get a whopping 60 percent of their calories from fat, all of it rich in essential fatty acids. Yet they have low rates of cardiovascular disease, diabetes, and cancer. [8]
The best advice with fats is the same as for any other topic in nutrition: choose what is known to be good, avoid what is known to be bad, and try to get a mix of everything in moderation just in case all the current knowledge turns out to be wrong!
Sources and References:
[1] http://www.americanheart.org/presenter.jhtml?identifier=532
[2] http://www.americanheart.org/presenter.jhtml?identifier=4776
[3] http://www.vnv.org.au/Nutrition/Omega3.htm
[4] http://www.nutritionnewsfocus.com
[5] http://www.uoguelph.ca/nhptc/Jessica1.html
[6] http://www.jrussellshealth.com/chocolate.html
[7] http://www.westonaprice.org/knowyourfats/skinny2.html
[8] Vanderhaeghe, Lorna R. Healthy Immunity Macmillan Canada, 2001.
[9] The Reader’s Digest Association. Foods that Harm, Foods that Heal Reader’s Digest, 1997.
[10] http://www.barleans.com/literature/flax/104-primary-cause.html