Lipids: The Basics

Now it’s time for the good stuff, fats! Fats (or lipids) have a reputation of being bad for the body, but tasting too yummy to resist. Everyone seems to know the downside to eating too much fat; for example, the increased risk of cardiovascular disease and, of course, weight gain. However, lipids do benefit the body. For instance, fats:

1.     Are energy reserves

2.     Provide padding around the vital organs

3.     Serve as a temperature buffer

4.     Majorly compose cell membranes (phospholipids)

5.     Transport fat-soluble vitamins and nutrients

There are several types of lipids: triglycerides, phospholipids, and sterols.

        Triglycerides are three fatty acid chains attached to a glycerol molecule. Which is just some chemistry talk to say that the molecule looks like a stick with three streamers hanging off of the side. The term “fat” actually refers to the term “triglycerides”. A triglyceride is the storage form of fat. The non-stored version of fats is the separate fatty acid chains and glycerol molecule floating in blood; they are long chains of carbon, oxygen, and hydrogens. Fatty acids differ from each other in chain length or types of bonds between carbon atoms. A saturated fatty acid is a chain with only single bonds between the carbons; put in another way, it is completely saturated with hydrogen atoms. Because their packed together tightly with single bonds they are solid at room temperature. Examples of foods with a high saturated fat content are:

• Butter
• Cheese
• Nuts
• Processed meat
• Animal fats

Unsaturated refers to fatty acid chains with double bonds between some of the carbons. Because some carbons have two bonds with each other, they have fewer chances to bond with hydrogen atoms. This causes a lower saturation of hydrogens and, due to the loosely packed double bonded chains; they are liquids at room temperature. The locations in the chain without hydrogens are referred to as points of unsaturation. Depending on how many points there are decides how an unsaturated fatty acid is named. A fatty acid with one point of unsaturation is referred to as a monounsaturated fatty acid and if it has two or more double bonds it is called a polyunsaturated fatty acid (which have different names depending on where the double bonds are; ex: omega-3 fatty acid and omega-6 fatty acid). Examples of unsaturated fats include:

Monounsaturated	Polyunsaturated
peanut butter	fish
olives	flaxseed
avocados	walnuts
olive oil	soymilk
sunflower oil	corn oil

The last kind of fatty acid is called trans fats. Usually, in a polyunsaturated fat, the hydrogens that bond with the carbon atoms are on the same side of the chain. In trans fats, one of the hydrogen atoms switches sides, resulting in the hydrogens being on opposite sides. Some trans fats occur naturally, and depending on how much you eat, they have a little effect on the body; however, synthesized trans-fatty acids behave somewhat like saturated fats in the body. Examples of food with trans fats are:

• French fries
• Twinkie
• Margarine
• Pancakes
• Fried chicken

In general, saturated fat is known as the “bad” fat and unsaturated fat is known to be “good”. But the truth is that both fats are necessary in the diet and beneficial to the body. The stereotype of “bad” and “good” comes from the idea that saturated fats are easier to overindulge in and, therefore, contribute more to weight gain. When selecting foods it is important to consider that even though unsaturated fat may be healthier, eating too much is still not healthy.

A phospholipid molecule is similar to a triglyceride, but instead of three fatty acid chains it only has two. Instead of a third chain it has a molecule that makes the phospholipid water soluble; therefore, these molecules have hydrophobic and hydrophilic (the fatty acid chains are fat soluble) portions. Phospholipids arrange themselves tightly to become the cell membrane; and because of their water-loving and fat-loving components, vitamins and hormones may easily enter the cell. Another function of phospholipids is to behave as an emulsifier (mixing fats in water).

Sterols are molecules composed of several ring like structures. An example of a sterol is cholesterol. Although cholesterol is best known for causing plaque to collect in the arteries (a disorder called atherosclerosis) which can lead to more serious conditions such as heart attacks and strokes, it is important to the body. For instance, cholesterol serves as the basis for:

• Bile acids
• Steroid hormones
• Vitamin D

and is a fundamental element for cell membranes.

There are several forms of lipoproteins that carry fats, they are very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). A VLDL carries mainly triglycerides to cells in the body to be used. Once a VLDL has donated its triglyceride molecules it becomes an LDL which hands out cholesterol to an accepting body tissue. HDL carries cholesterol from the body cells back to the liver to be disposed. Typically, LDL is known as the “bad” cholesterol and HDL is known as “good”; but it’s important to keep in mind that these lipoproteins are carrying the same cholesterol compound; the difference is where they are taking the sterol. Both are important for normal body function, it can become troublesome when there is a lot of cholesterol that can be given out to the body cells. This doesn’t make LDL “bad”, it just makes it easier to be affected by unhealthy eating habits.

The take home message of this post is that fats are beneficial in moderation.  

• Hannah