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Transcript:
For decades, the relationship between dietary fats and health was at the center of our attempts to understand the underlying cause of our obesity epidemic.

Michael Pollan: The debates over nutrition that you will hear, should we worry about fats, should we worry about carbohydrates, is the problem lack of fiber? All these are attempts to understand what's the problem in the Western diet that is the culprit.

Despite the important roles that fats play in our bodies, this entire category of macronutrient, was shunned for much of the 20th century. This led to an enormous increase in the availability of fat free and reduced fat foods, but despite this, obesity rates continued to rise. Today, rising awareness about the difference between what some people call “good fats” and “bad fats” have allowed this important part of our food supply to make a comeback, but once again, the pendulum threatens to swing too far in the opposite direction.

Dietary fats can be divided into two families: the saturated and the unsaturated fats. Saturated fats get their name from the fact that their fatty acids are saturated with hydrogen molecules. This means that they can lie flat and pack together densely, so that saturated fats tend to be solids at room temperature. Animal fats like lard and butter are good examples. In contrast, the fatty acids that make up unsaturated fats are kinked in places where double bonds between the carbon atoms cause the chains to be less saturated with hydrogen. This also means that these fatty acids don’t pack together as tightly, leaving most unsaturated fats in the liquid state at room temperature. But unsaturated fats can be naturally occurring, like the fats found in olive oil, nuts and avocados… or they can be man-made, (or chemically manipulated) to become unsaturated. These are the fats found in some margarines and in the kinds of oils that are often used for repeated cooling and re-heating in deep frying machines – like the ones used in many fast food restaurants. The problem with chemically engineered unsaturated fats is that the chemical bonds between the carbon atoms are less stable, so they easily flip into a trans orientation rather than a cis orientation – and this is where we get the name trans fats.

Trans fats are problematic for our health because they increase the amount of LDL cholesterol in the blood and by doing this, they promote the formation of arterial plaques. At the same time, trans fats reduce the amount of HDL, the protective form of cholesterol, in our blood and the result is a greatly increased risk of atherosclerosis and heart disease. While saturated fats have also been shown to contribute to increases in LDL cholesterol, they haven’t been shown to lower HDL cholesterol or to contribute to the development of arterial plaques as significantly as trans fats.

Probably the most sensible food recommendation that results from the accumulated scientific studies of dietary fats is this: Enjoy reasonable amounts of foods that contain mostly naturally occurring unsaturated fats, like those found in olive oil, nuts and avocados. Avoid all foods containing trans fats, and limit your intake of foods, like red meats, that are high in saturated fats.

Course by Maya Adam, MD
Directed by William Bottini
Editing by William Bottini & Tamsin Orion
Special thanks to Michael Pollan, Tracy Rydel, and David Eisenberg

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