Monday, December 13, 2010

The Difference Between Solid and Liquid Fats

Have you ever wondered what the difference is between a fat that is liquid and a fat that is solid at room temperature?

Building blocks of fat

Let's begin by explaining why room temperature fats are solid or liquid. Fats are liquid or solid according to their chemical make up or how their building blocks are stacked together. Imagine a tower of tightly stacked blocks. The close packing of these blocks is similar to the tightly packed molecules that make saturated fats appear solid.  The building blocks of unsaturated fats have bends or kinks that don't allow the blocks to be tightly stacked and thus, appear more fluid and are liquid at room temperature.

Liquid fats

In general liquid fats come from plant oils and are unsaturated fats. Olive, canola, corn, soybean, safflower and sesame oils all come from plants. One exception of a liquid fat not from plants is fish oil. 

Solid fats

In general, fats that are solid at room temperature come from animals and are saturated fats. Picture a marbled steak or the skin of a chicken. Butter is another example of a fat that is solid at room temperature. It is a mixture of 66-percent saturated fat and 30-percent monounsaturated fats.

There are a few exceptions where saturated fats are found in plant foods. These include coconut oil and avocado, which contain some saturated fat along with mostly mono-unsaturated fat.  Another exception is a processed fat called trans-fats. These are plant oils that behave like saturated fats because their building blocks have been altered and can stack tightly to be solid at room temperature. Trans-fats have been shown to be harmful to our health, and are the top-priority recommendation of the type of fat to be avoided. Look for the words "hydrogenated" or "partially hydrogenated" oils in the ingredient list to know if a processed food contains trans-fats.

Now you have the basics about the structure that determines whether fats are liquid or solid. Fats are an essential part of the diet and the general rule of thumb is that they should comprise about 30 percent of your daily calories, with no more than 10 percent being saturated fat. To learn more about including a variety of healthy fats in your diet, consider scheduling an appointment with a registered dietitian and get on the path to better health.

-Marcy Johnson, dietetic intern, and Debra A. Boutin, MS, RD, chair and dietetic internship director, Department of Nutrition and Exercise Science at Bastyr University

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