Are lipids such as fat and cholesterol bad for us?
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Over the past couple of decades fat and cholesterol have taken a beating in the press, being labeled as the nutritional “bad boys”. Often we are told to avoid them as much as possible. However, today we are told that we do indeed need fat, especially certain types of fat that might support cardiovascular and joint health as well as help support the maintenance of memory and cognition later in life. Cholesterol from food, on the other hand, might not be as potent a blood cholesterol raiser as we once thought. So which types of fat are better for you and which are more expendable from the diet? |
What are lipids?
Fats and cholesterol belong to a special group of molecules called lipids. The members of this club have something pretty significant in common: they are relatively insoluble in water. This might not seem like a big deal, but keep in mind that most of our planet’s surface is water and, more important to our topic, most of our body is water as well. Because of their inability to dissolve into water, we must make special concessions to accommodate lipids both during digestion and also inside of the body.
During digestion, an emulsifying substance called bile is called to action to facilitate lipid digestion and absorption. As for fat and cholesterol inside of the body, they require special transport shuttles to circulate. Fat also has its own cell type specifically designed for storage. These cells are called adipocytes, or more commonly “fat cells,” and large collections of adipocytes are called adipose tissue. Adipose tissue is found under the skin (subcutaneous fat) and in deeper deposits (visceral fat) such as in the abdomen, around vital organs, and throughout skeletal muscle.
What is the difference between fat, oils, and triglycerides?
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Fats and oils are terms commonly used to refer to food sources of triglycerides. Often fat and oil are considered to be different based on appearance: fat is solid at room temperature and oil is liquid. However, they are really two of the same thing, generally speaking. They are both collections of triglycerides. For simplicity, we will use “fat“ to include all sources of tri–glycerides. |
A triglyceride molecule is a combination of three fatty acids linked to a glycerol molecule backbone (see Triglyceride and Phospholipid Figure). Although a triglyceride molecule will always have this general design, there can be great variability in the type and combinations of fatty acids that link to glycerol. Only one glycerol molecule exists, but like monosaccharides there are numerous different types of fatty acids in nature. Also, if a triglyceride involves three fatty acids then monoglycerides and diglycerides will have one and two fatty acids attached to glycerol, respectively. Technically, they can be considered fat as well.
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