When speaking to a group recently about different kinds of cooking oils, focusing most specifically on olive oil and its grading level, I was asked the question, "what's different about light olive oil?" To which I dryly responded...
"It's a farce."
Minds were blown. The bulk of the group couldn't believe it at first, until I started explaining what's really going on with "light" olive oil.
As consumers, we've been trained, by way of slick advertising and snazzy labels, to believe that the term "light" means that the product is in some way healthier for you, with what's assumed to mean a lower fat or calorie content. The USDA monitors food labeling in our country, which is meant to protect the consumer from purchasing goods without some semblance of knowledge of what they're buying, but not all food products are created or monitored equally.
For instance, the USDA's Food Safety and Inspection Service's (FSIS) definition for "light" or "lite" is as follows:
"If a product derives 50 percent or more of its calories from fat, its fat content must be reduced by 50 percent or more per RACC as compared to an appropriate reference food."
More or less, this is what we, as consumers know of the term, and we assume that its definition is universal... but it isn't.
So what's the difference between light and non-light olive oil?
Nutritionally speaking, there isn't one. Confusingly, the term "light" and/or "extra light" in the olive oil world is completely different than what you'd see with meat, dairy, and poultry products. The "lightness" of our off-the-shelf supermarket olive oils is significant of two things:
Color and Flavor.
True Extra-Virgin olive oil is never refined; the process of refinement would negate the "virginity" of the oil... that is to say, for it to be refined someone would have had to tamper with the oil, therefore it cannot be considered Extra-Virgin.
The Olive Oil industry is one of the least-regulated (at least in the U.S.), and most corrupt businesses on the planet. Fraud is rampant, and it typically involves disguising and/or blending of lower grade and quality oils (and I'm not talking just olive oils) as Extra-Virgin olive oil. Lower grade oils are usually deemed "not fit for human consumption," and are then refined to crude olive oil, or refined to remove defects that could be considered a potential health risk, and then they're either artificially or naturally flavored and colored to look like Extra-Virgin olive oil.
Here's where our "light" olive oil comes back into the picture...
In the eyes of large-scale foreign producers, the U.S. consumer's palate is not accustomed to the definitively bold, bitter, spicy, and unctuous flavors of true Extra-Virgin olive oil. As a result, these distributors buy massive quantities of low-grade oil, blend it with varying amounts of Extra-Virgin oil to flavor and color it, and sell it in our supermarkets as "Light" and "Extra Light" (depending on how much Extra Virgin was used to flavor and color it). The U.S.D.A. only recently published standards for olive oil grades, but for one, the grading process is voluntary, and two, they have nothing to do with the "lightness" of an olive oil; those standards define what is and isn't Extra-Virgin.
The process by which oils are refined breaks them down to their most simplistic component: fat. It's meant to remove any unwanted flavors, odors, or colors. The many ways that oils are refined ultimately remove all of the polyphenols, which are naturally occurring chemical compounds that offer huge and numerous health benefits, from olive oil specifically.
So, what did I mean by calling the "lightness" of oil a farce?
Everyone in that room thought they were buying "light" olive oil because it was healthier. In reality, "light" olive oil, a refined and sometimes artificially flavored product, is actually less healthy than real-live Extra-Virgin.
For more info on olive oil, read see any of the numerous books written about its production and health benefits. Specifically, I'd go with Tom Mueller's Extra Virginity to get a grasp on the extent of the counterfeit culture of olive oil in Europe, and also Cal Orey's The Healing Powers of Olive Oil to see some of the amazing things that Extra Virgin olive oil can do for your body.