One clue will be an overview of how fats behave in temperature. They range from always being a solid at room temperature and stable in heat to only becoming a solid in the freezer and very unstable in heat.
Processed, fabricated fats like;Crisco and saturated margarine remain solid at almost any room temperature and almost never go bad....
Safflower, corn, soy and sesame oil stay liquid, even in the refrigerator. These vegetable-derived oils are natural, but highly-unstable and easily damaged by heat. As a result, they should not be used for cooking.
Heat-sensitive oils like those from flax, hemp, and fish should be kept refrigerated to preserve and protect them. They should never be exposed to heat and will solidify only when frozen.
See the trend?
The more solid at room temperature a fat is the more resistant it is from going rancid with heat as well as to light and oxygen.
Do you know why?
It all has to do with how these fats are structured. From a chemical standpoint, it becomes important to evaluate how many double bonds each type of fat contains. This is when the terms polyunsaturated, monounsaturated, and saturated all come into play.
I won’t get into the specific organic chemistry of fats other than to remind you that all fats are a long, carbon-linked (bonded) chain with hydrogen and oxygen attached.
Here’s your cheat sheet:
A saturated fat has double bonds between all the carbon chains.
When a fat is missing a double bond, it’s called unsaturated.
If it’s missing only one double bond, it’s called monounsaturated.
If it’s missing more than one double bond, it’s called polyunsaturated. These type of fats can be missing usually anywhere from 2 up to 6 double bonds.
So why is this important?
The more double bonds a fat is missing, the more flexible it becomes but the trade-off comes at making it more susceptible to heat, light and oxygen damage. (This is where our bodies antioxidant protection comes into play.)
And these different fat structures are the result of nature’s grand plan for protecting naturally-occurring oils from heat, oxygen, and light while accommodating their varying needs for structural flexibility in variety of environments.
With this information in hand let’s revisit the range of fats.
Crisco and hard margarines stay hard forever as they are artificially-created saturated fats. For decades now, food manufacturers have been implementing a chemical process to turn cheap, polyunsaturated oils into a processed, fat-like substance that will stay “fresh” for months (or even years) at room temperature. While this is good for manufacturers and merchants, it’s bad for you—the end consumer; this profitable, chemical process is the reason for the ever-increasing incidence of trans-fat related disease.
In high-temperature, tropical climates, there is no need for structural flexibility but a great need for heat protection. Saturated fats including coconut and palm kernel oils as well as animal fats (which are produced by warm-blooded animals) are nature’s solution.
In moderate temperature zones (like the American Midwest), oils have a lesser need for flexibility and a greater need for heat protection. These oils (corn, canola, soy, and safflower) are naturally less polyunsaturated.
In warm temperature regions (like the southern U.S. and Mediterranean), there is an even lesser need for flexibility and greater need for heat protection. The resulting oils—olive, peanut, avocado, and macadamia—are all monounsaturated.
Fats sourced from cold-temperature organisms (like fish, algae, and krill) or crops grown in cold temperatures (such as flax, chia, and hemp) are highly polyunsaturated because they need to stay flexible; in their natural environment, they would not be exposed to heat.
Your take home message:
Because of their high heat stability, saturated fats (and some mono-unsaturated oils such as avocado and macadamia oils) are the best choice for cooking—as they can withstand higher temperatures without being damaged.
On the other hand, polyunsaturated fats such as corn, soy, sesame and canola, because they are susceptible to heat damage, should never be used for cooking and highly polyunsaturated oils (like those from flax, hemp, and fish) are so susceptible to damage, they should need only be protected from heat but from oxygen and light as well. They should be kept refrigerated in an opaque container, and used within 45 days after opening.
What’s next? I’ll discuss why healthy fats are the body’s best friend. And why we shouldn’t allow a few bad fats to ruin our relationship with them.