Retrospective #20: Know Your Dietary Fats: Saturated and Unsaturated

“Let food be thy medicine and medicine be thy food”: Hippocrates (460BC - 370BC). If you are going to take an interest in your health, as the “father of medicine” sagely advised, you need a basic understanding of nutrition.

So, let’s begin with the classification of fats into Saturated and Unsaturated. Saturated fats are solid at room temperature and unsaturated fats are liquid. In the 2010 “Dietary Guidelines for Americans,” the USDA/HHS has begun to use “saturated fat” and “solid fat” interchangeably. In the HHS’s new “food pyramid”, the HHS never uses the macronutrient word “fat.” It calls all unsaturated fats “oils.” Do you find this nomenclature confusing? I do.

Saturated fats are for the most part animal fats, i.e. fats found in intramuscular tissue as well as under the skin and around the organs. Both in the animals we eat, and in our own physiology, fat serves as both an energy source and an energy reserve. It also cushions the organs and skeleton from damaging blows and insulates the body from cold.

More recently – and this is a development of monumental importance in our understanding of fat metabolism -- fat stores have come to be recognized as an endocrine organ as well. Leptin, a hormone discovered in adipose (fat) tissue in 1994, is an appetite suppressant, sending a strong signal to the hypothalamus at the center of the brain. Our fat is in a constant state of flux as its primary form, triglyceride molecules, are being created or broken down.

Two other saturated fats (both solid at room temperature) that are commonly found in foods are vegetable in origin: Both are tropical oils – coconut oil and palm oil. Coconut oil, a medium-chain saturated fat, is appearing with increasing frequency in the Western Diet, but both have been used in cooking for millennia in tropical regions.

Saturated fats are solid because of their dense structure, with every carbon atom along the carbon chain having two hydrogen atoms. In addition, as it has no “double bond” between carbon atoms, they are straight, packed closely together and thus solid. Since there are no “free” atoms, they are also very stable and are not liable to become rancid when exposed to oxygen. It also means that, in their normal state or in cooking they will not create harmful “free radicals” or, when heated, produce pro-inflammatory AGE’s (Advanced Glycation End-Products).

Unsaturated fats break down into two sub-classes: monounsaturated and polyunsaturated. Monounsaturated fats are primarily found in olive oil, and to a lesser extent in Canola oil and peanut oil. Additional sources are avocado and some popular nuts (macadamias, pecans, hazelnuts). They are called monounsaturated because they have only one “double bond” in the carbon chain. They are fairly tightly packed and fairly stable when heated or exposed to oxygen (as in air). Have you noticed how olive oil becomes solid when refrigerated? It is, therefore, safe to use.

Polyunsaturated fats are fats that have more than one double bond in the carbon chain (hence poly), and are therefore loosely constructed and usually found in the liquid state as “oils” (see the exception for trans fats below). Because of their loose construction, they are relatively unstable, “reactive,” and rather easily become rancid. They are also easily damaged by heating (as in a deep fryer) and especially when reheated over and over.

These polyunsaturated fats are the vegetable oils that are now ubiquitous in our food supply due to their ability to be manufactured cheaply. But refining and processing also has deleterious effects that are becoming increasingly known and understood. Trans fat is an example. It is a liquid vegetable oil that has been “hydrogenated,” or “partially hydrogenated,” to make it solid for use as margarine and in manufactured baked goods and cooking. There is a now broad consensus that everyone should strictly avoid artificial trans fats. Read food labels carefully to avoid all hydrogenated oils because portion size provides a “workaround” that is used to deceive us.

Finally, all fats are combinations of all three types: saturated, monounsaturated and polyunsaturated. Butter, for example is 66% saturated, 30% mono and 4% poly. Olive oil is 15% saturated, 70% mono and 10% poly. Soybean oil, used in 70% of processed foods and most restaurants in the US, is 15% saturated, 22% mono and 62% polyunsaturated (the worst!). Takeaway: Saturated and monounsaturated fats: good. Polyunsaturated fats: bad!