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Lipids

Aim: What are lipids?

Objectives:

-Explain the chemical make-up or parts of a lipid.

-Explain fats and oils.

-Explain saturated, unsaturated, and polyunsaturated fats.

-Explain the usage of lipids for body parts and energy.

-Explain the types of food to find lipids.

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Do now: Analyze diagram and copy a “triglyceride molecule”.

Molecules made of carbon and hydrogen present at the same time in a molecule is an organic molecule.

Triglyceride molecule is made of four parts: One glycerol molecule and three fatty acids.

A triglyceride is a fat if it is solid at room temperature and an oil if it is liquid at room temperature.

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Lipids that have tail chains with only single bonds between the carbon atoms are called saturated fats.

Lipids that have at least one double bond between carbon atoms in the tail chain are called unsaturated fats.

Fats with more than one double bond in the tail are called polyunsaturated fats.

Fats are the most concentrated energy source available to the body. Lipid is used as a secondary source of energy and produces more energy (ATP molecules) than carbohydrates.

Lipids are more dangerous than carbohydrate to be used. Lipids that can clog (block or stop) the blood vessels (example arteries) are saturated fats. The clogging of the blood vessels can cause heart attack and/or cerebral strokes.

Building blocks for the body, which is used to cushion organs in the body and for cell membrane.

Meats and cheeses are sources of saturated fats.

Plants are the main source of unsaturated fats.

Key questions:

-Explain why are lipids considered organic?

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-What are the two different parts to make lipids?

-Explain the different between fats and oils.

-Explain what constitutes a saturated fat?

-Explain what constitutes an unsaturated fat?

-Explain what constitutes a polyunsaturated fat?

-Explain why lipids are important for the human body?

-How does our body obtain lipids or/and what type of foods contain lipids?

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Plant Cell

Nuclearenvelope

Ribosome(attached)

Ribosome(free)

Smooth endoplasmicreticulum

Nucleus

Rough endoplasmic reticulum

Nucleolus

Golgi apparatus

Mitochondrian

Cell wall

CellMembrane

Chloroplast

Vacuole

Animal Cell

Centrioles

NucleolusNucleus

Nuclearenvelope

Rough endoplasmic reticulum

Golgi apparatus

Smooth endoplasmicreticulum

Mitochondrian

CellMembrane

Ribosome(free)

Ribosome(attached)

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Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel

Lipid bilayer

Carbohydratechains

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Why is it important to read the nutritional fact label?

Nutritional label from a bottle of olive oil

FatsWe all know about the common fats that different foods contain. Meat contains animal fat. Most breads and pastries contain vegetable oils, shortening or lard. Deep fried foods are cooked in heated oils. Fats are greasy and slick.

You commonly hear about two kinds of fats: saturated and unsaturated. Saturated fats are normally solid at room temperature, while unsaturated fats are liquid at room temperature. Vegetable oils are the best examples of unsaturated fats, while lard and shortening (along with the animal fat you see in raw meat) are saturated fats. However, most fats contain a mixture. For example, above you see the label from a bottle of olive oil. It contains both saturated and unsaturated fats, but the saturated fats are dissolved in the unsaturated fats. To separate them, you can put olive oil in the refrigerator. The saturated fats will solidify and the unsaturated fats will remain liquid. You can see that the olive oil bottler even chose to further distinguish the unsaturated fats between polyunsaturated and monounsaturated. Unsaturated fats are currently thought to be healthier than saturated fats, and monounsaturated fats (as found in olive oil and peanut oil) are thought to be healthier than polyunsaturated fats.

Fats that you eat enter the digestive system and meet with an enzyme called lipase. Lipase breaks the fat into its parts: glycerol and fatty acids. These components are then reassembled into triglycerides for transport in the bloodstream. Muscle cells and fat (adipose) cells absorb the triglycerides either to store them or to burn them as fuel.

You need to eat fat for several reasons:

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As we will see in the next section, certain vitamins are fat soluble. The only way to get these vitamins is to eat fat.

In the same way that there are essential amino acids, there are essential fatty acids (for example, linoleic acid is used to build cell membranes). You must obtain these fatty acids from food you eat because your body has no way to make them.

Fat turns out to be a good source of energy. Fat contains twice as many calories per gram as do carbohydrates or proteins. Your body can burn fat as fuel when necessary.

Between the food commercials you see on TV every day and the many nutrition bulletins and reports you hear about on the news every night; you get a huge amount of information about the fats that you eat. For example, you have probably heard of the following terms:

Saturated fat Unsaturated fat Polyunsaturated fat Mono-unsaturated fat Fatty acids Essential fatty acids Trans fatty acids Omega-3 and omega-6 fatty acids Partially hydrogenated fat

Have you ever wondered what it all means, or why it matters? Why can't we just eat, drink and be merry? In this article, you'll find out exactly what these terms mean and how the various forms of fat you find in foods affect your body. But first, let's find out what we're talking about in practical terms.

We see pure fats in three places at the grocery store:

In the vegetable oil aisle you see oils created from different seeds and nuts. There is corn oil, safflower oil, peanut oil, canola oil, olive oil... All seeds and nuts contain some amount of oil, because oil is a very good way to store energy. By the way, the only difference between oil and fat is whether or not it is a solid at room temperature.

In the meat aisle, you can look at different cuts of meat and see them outlined by a layer of white, solid fat created by the animal to store energy.

In the dairy aisle you see butter and margarine -- fat made from cream or vegetable oils, respectively.

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The rest of the grocery store is, of course, filled with fats and oils, although they are less obvious. Potato chips and French fries are cooked in oil, cookies and cakes contain fats and oils, and so on. This is how we come to eat the fat we need every day. And we do need fat -- as you will learn in this article, there are certain fats that we must have to survive.

So what are these fats and oils really made of? Well, if you really want to understand fat you need to study a little bit of chemistry. To talk about fat, we need to start by talking about fatty acids.

Corn Oil

With some grains and nuts it is very easy to see where the oil comes from. For example, if you squeeze a sesame seed or a sunflower seed between two sheets of paper, you can see the oil. Corn isn't quite that oily, but it does contain oil. A kernel of corn has an outer husk surrounding a white or yellow starchy substance. At the core of the starchy substance and toward the pointy end of the kernel is the germ. The germ contains a small amount of oil. If you cut a popcorn kernel in half, you can see the husk, starch and germ. If you cut out the tiny piece of germ and squeeze the germ on a piece of paper, you will see the oil!

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What is a Fatty Acid?A fatty acid is a long hydrocarbon chain capped by a carboxyl group (COOH). There are many common fatty acids that you hear about, four of which are shown below along with acetic acid for comparison:

The COOH cap is what makes these molecules acids. You are probably familiar with acetic acid because this is the acid found in vinegar. You can see that the fatty acids are like acetic acid, but they have much longer carbon chains.

To make a normal fat, you take three fatty acids and bond them together with glycerol to form a triglyceride, like this:

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Since this particular triglyceride happens to contain three molecules of stearic acid, it is also known as tristearin. This diagram shows one fat molecule. When you eat fat, you are eating collections of molecules like these. The choice of the fatty acids in the fat controls many different things about the fat, including how it looks, whether it is a solid or a liquid at room temperature and how healthy it is for your body. Many of these characteristics have to do with whether a fat is "saturated" or "unsaturated."

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Saturated vs. UnsaturatedIf you look at palmitic acid and stearic acid chains, you can see that the carbon chains are completely and evenly filled with hydrogen atoms.

In other words, the chains are saturated with hydrogen. Fats (triglycerides) that contain palmitic acid and stearic acid are therefore known as saturated fats. Fats made up of saturated fatty acids are solid at room temperature. You can also see that oleic acid is not saturated. Two of the carbons are connected by a double bond, and two of the hydrogens are missing. This fatty acid is unsaturated. Fats that have a lot of oleic acid in them are liquid at room temperature, and are therefore known to us as oils.

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Oleic acid, because it contains one double bond, is also referred to as mono-unsaturated. Fatty acids that have multiple double bonds, like linoleic acid in the first figure, are called polyunsaturated. Polyunsaturated fats are also liquid at room temperature.

If you have a bottle of corn oil, what you have is a bottle of polyunsaturated oil with a high concentration of linoleic acid. Because it is polyunsaturated, it is liquid at room temperature. If you would like to solidify it and turn it into margarine, what you do is hydrogenate it. That is, you saturate it with hydrogen by breaking the carbon double bonds and attaching hydrogen. To do this, you heat the oil and add pressurized hydrogen gas and a nickel catalyst. In this way, you create "partially hydrogenated vegetable oil." PHVO is the main ingredient in things like vegetable shortening and margarine.

Clogged Arteries

The heart is an amazing organ. It beats thousands of times each day, every day, for your entire life. In the process, it pumps about five million gallons of blood through your body!

The heart is a muscle, and it needs a supply of oxygen-rich blood to survive. Even though the heart has all of that blood flowing through it while it is pumping, it does not use that blood for its oxygen needs. Instead, there is a set of arteries and veins out on the surface of the heart muscle that feed it. If one of these outer arteries gets blocked, it causes a heart attack. A blockage like this is normally caused by fatty deposits that build up in the heart's arteries over the course of many years. Everything you hear about fat in the diet, cholesterol, coronary artery disease and "clogged arteries" is focused on this problem -- blocked heart arteries and the heart attacks they cause are a leading killer in the United States.

Fat and HealthMost of the nutrition science you hear about right now points to mono-unsaturated fats as the good fats. Olive oil and canola oil are both mono-unsaturated. Mono-unsaturated fats are thought to lower cholesterol.

In general, the fats to steer clear of are the saturated fats. Saturated fats are bad because they clog your arteries. Partially hydrogenated vegetable oils (which are artificially saturated fats) are now considered totally evil, both because of the saturation and a side-effect of hydrogenation called trans fatty acids.

Fatty acids that have double bonds come in two forms: trans and cis. "Trans" and "cis" refer to the direction of folding that occurs at the carbon double bonds in unsaturated fatty acids. Cis fatty acids are the normal, natural directions for the folds. A trans fatty acid is chemically identical to the cis form, but folds in an unnatural direction. The trans fatty acids are created by heat (as in deep frying) and by hydrogenation.

It turns out that in the body, the enzymes that deal with fat are unable to deal with the trans fatty acids (see How Cells Work for details on enzymes). Therefore, the enzymes get tied up trying to work on the trans fatty acids, and this can lead to problems with the processing of essential fatty acids.

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Essential fatty acids are not bad for you the way trans fatty acids are. They're actually essential to good health.

Essential Fatty AcidsThe most common fatty acids are found in animal fats and include:

Palmitic acid Stearic acid Oleic acid

Your body is able to create these fats whenever it has a caloric surplus. It can create them from straight sugar if there are enough sugar calories coming in (see How Food Works for a discussion of carbohydrates and sugar).

It turns out that there is another class of fatty acids called essential fatty acids that your body cannot manufacture. These fatty acids include:

Linoleic acid (LA) (omega-6) Arachidonic acid (AA) (omega-6) Gamma linolenic acid (GLA) (omega-6) Dihomogamma linolenic acid (DGLA) (omega-6) Alpha linolenic acid (LNA) (omega-3) Eicosapentaenoic acid (EPA) (omega-3) Docosahexaenoic acid (DHA) (omega-3)

Because your body cannot manufacture them, they must come in from the food you eat.

Essential fatty acids fall into two groups: omega-3 and omega-6. The 3 and 6 refer to the first carbon double bond position on the fatty acid chain. All essential fatty acids are polyunsaturated, so the 3 and the 6 mean that the first double bond is either 3 or 6 carbons in from the end.

Omega-6 fatty acids are everywhere: corn oil, sunflower oil and soybean oil all contain them. Omega-3 fatty acids are harder to find. Things like flax seeds, pumpkin seeds and walnuts are high in omega-3 fatty acids, as are salmon, trout and tuna. Current thinking is that these two fats need to be balanced in the diet at a ratio like 1-to-1 or 2-to-1, rather than the normal 20-to-1 ratio seen in most Western diets. About the only way to do that is to supplement your diet with omega-3 vegetable oils or to start eating fish in a big way (meaning two or three times a week).

Summarizing all of this information, the current scientific thinking on fat consumption goes something like this:

Limit your fat intake to about 30 percent of the total calories you consume. Do not try to cut fat intake altogether, because you do need the essential fatty acids. A gram of fat has nine calories, meaning that if you consume 2,000 calories in a day your total fat intake should hover around (2000 * 30 percent / 9 calories/gram) 67 grams of fat.

When consuming fat, try to focus on mono-unsaturated fats like olive oil and canola oil, or on essential fatty acids.

When consuming essential fatty acids, try to balance your intake of omega-6 and omega-3 fatty acids. Do that by consuming tuna/salmon/trout or omega-3 oils like flax seed oil.

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