Basic Nutrition Lesson Three - Fats

An Introduction to Fats

Fat is the substance in food that provides a rich texture and flavor. The foods that contain the largest amounts of fat come from animal products such as meat, dairy and eggs, plus nuts and seeds. Common examples of cooking fats include olive oil, lard, canola oil, walnut oil, butter, margarine and shortening.

Fat has gotten a bad reputation in the diet world, although only some of that reputation is deserved. While bad fats can cause bad health, good fats are needed for good health. This lesson will help you understand a little more about the fats you need and the fats to avoid.

A Little Bit of Fat Chemistry

Fats and oils are made up of individual molecules called fatty acids. Fatty acids are chains of carbon and hydrogen atoms that have a carboxyl group at one end and a methyl group at the other.

Carboxyl groups include one carbon atom and three hydrogen atoms and methyl groups contain one carbon atom, one hydrogen atoms and two oxygen atoms. The carbon atoms in the fatty acid molecules are linked together by single or double bonds.

Fatty acids vary in length. Short chain fatty acids have two to four carbon atoms, medium chain fatty acids have six to 12 carbons atoms, long fatty acids have 14 to 18 carbon atoms. A few fatty acids have more than 20 carbon atoms chains.

Fatty acids are either saturated or unsaturated. Saturated fatty acids have no double bonds between any of the carbon atoms in the chain. Unsaturated fatty acids have one or more double bonds in the carbon chain. Monounsaturated fatty acids have one double bond and polyunsaturated fatty acids have two or more double bonds. Unsaturated fatty acids are sometimes named by the position of the double bonds in the carbon chain. The names Omega-3,-6 or -9 refer to the locations of the first double bond in the the three different fatty acid molecules.

Unsaturated fatty acids can have two different configurations of the hydrogen atoms on either side of the double bonds. Cis configurations have those hydrogen atoms both on the same side of the molecule. This causes the molecule to look like it is bent. Trans configurations have those hydrogen atoms on opposite sides of the double bond. This gives the molecule a more linear appearance, like saturated fats. Interestingly, it turns out that both saturated fats and trans fats are bad for your health.

Most of the fats in the food you eat are fat called triglycerides. A triglyceride is made up of three fatty acid molecules attached to a glycerol molecule. The types of fatty acids in the triglycerides have an important impact on the physical state of the fats you eat. Fats that are composed of triglycerides with saturated fatty acids, like meat, are solid at room temperature. Fats that are composed of triglycerides with unsaturated fatty acids, like vegetable oils, are liquid at room temperature. Your body will use triglycerides as energy or store them as adipose tissue.

The foods you eat may also include cholesterol. Cholesterol does not produce any energy like triglycerides, but it is important for many biochemical processes and hormone production. Elevated cholesterol levels in your body have been associated with an increased risk of cardiovascular disease. The cholesterol in your body is mostly made in your liver and there are three different types: High Density Lipoproteins, Low Density Lipoproteins and Very Low Density Lipoproteins. Having higher HDL cholesterol levels can decrease your risk of cardiovascular disease, however elevated LDL cholesterol will increase that risk.

Fat Functions in the Body

Fats and cholesterol have a number of important functions, which include:

Lubrication of body surfaces
Components of cell membrane structures
Formation of steroid hormones
Energy storage
Insulation from cold
Carrying fat soluble vitamins A, D, E, K

Saturated Fats and Your Health

Saturated fats are made up of triglycerides that have saturated fatty acids. These fats are solid at room temperature. They come mostly from animal sources, although there are saturated fats in coconut oil, palm oil and palm kernel oil. Saturated fats found in red meat, butter, milk, cheese and eggs will increase cholesterol levels in the body. In fact, saturated fat will raise your cholesterol much more than dietary cholesterol does. Eating a diet rich in red meat has been linked to an increased risk of cardiovascular disease and some cancers. Since red meat has the highest concentration of saturated fats, most experts suggest that you limit your consumption of red meat to only two or three times per week.

Monounsaturated Fats, Polyunsaturated Fats and Your Health

Monounsaturated fats are made up of triglycerides that have monounsaturated fatty acids. Monounsaturated fats are liquid at room temperature but solid when they are refrigerated. Olive oil contains a monounsaturated fat call oleic acid, and is the best-known monounsaturated fat. Canola oil, peanuts and avocados also contain some monounsaturated fats. Consumption of monounsaturated fats has been shown to decrease LDL cholesterol levels and elevate HDL cholesterol. Olive oil and canola oil are both great choices for cooking.

Polyunsaturated fats also help to keep your cholesterol levels in check. Polyunsaturated fats are made up of triglycerides with polyunsaturated fatty acids. Polyunsaturated fats come mostly from plant sources like nuts, seeds and vegetable oils.

These fats are liquid at room temperature and often stay liquid when refrigerated. Fish is also good source of polyunsaturated fats, especially cold water, oily ocean fish. This is why you should eat fish at least three times per week. While most red meat is low in polyunsaturated fats, animals raised on grass offer red meat that has more polyunsaturated fats than corn-fed beef.

Omega-6 and Omega-3 Essential Fatty Acids

The essential fatty acids are so named because you need to get them from your diet. Your body can make many of the fatty acids it needs from other types of fatty acids, but the omega-6 and omega-3 polyunsaturated fatty acids must come from the diet. Omega-6 fatty acids come from vegetable oils, nuts, and seed oils. Good sources of omega-3 fatty acids include walnut oil, canola oil, fish, soy and flax. The omega-6 fatty acids are very prevalent in a typical western diet, however omega-3 fatty acids are often deficient. Eating the right balance of these fats is important for controlling inflammation, healthy cell membrane structure and brain development. Omega-3 essential fatty acids will also help to regulate heart rhythm and keep your cholesterol levels healthy. When you don't get enough of the essential fatty acids in your diet, you may have dry skin, dry hair and more inflammation.

Trans Fats

Most trans fats are created artificially by a process called hydrogenation. This involves heating regular vegetable oil and forcing hydrogen atoms onto the polyunsaturated fatty acid molecules. This process turns the oil into a solid substance and improves the shelf life of the fat. Fully hydrogenating a vegetable oil will make it very firm. Partially hydrogenated oils are softer and are widely used in baked goods and processed foods. Examples include stick margarine, partially hydrogenated frying oils, donuts, snack cakes, cookies and processed foods. Artificially created trans fats are the unhealthiest of fats, even worse than saturated fat. Eating too many trans fats has been linked to increasing your risk of cardiovascular disease.

Not all trans fats are created in the lab. There are small amounts of natural trans fats that occur in milk and beef. Conjugated linoleic acid is a well known natural trans fat. The natural trans fats do not appear to be as unhealthy as the artificial trans fats.

Fat Digestion

The digestion of fat begins in the mouth with lingual lipase. Lipase is a digestive enzyme that breaks fatty acids apart from triglycerides. Fat stays in the stomach longer than carbohydrates. That is one reason why fat is so satisfying. There is a small amount of lipase in the stomach, however most fat digestion occurs in the small intestine.

Fat in the small intestine is mixed with bile. Bile is released from the liver and gall bladder and works like a detergent to emulsify dietary fats into smaller droplets. This makes it easier for a digestive enzyme called lipase to get to the triglycerides. Lipase is made by the pancreas and secreted into the small intestine. The fats are absorbed from the digestive contents into the blood stream. The bile, which contains cholesterol, is either re-absorbed into the blood or bound by soluble fiber in the intestine and eliminated in the stool. Eating foods with lots of soluble fibers helps to keep your cholesterol levels healthy by grabbing more of the cholesterol from the bile and eliminating it because fiber cannot be digested.

A healthy digestive system will absorb about 95 percent of the dietary fat that you eat. People with malabsorption disorders will not be able to absorb fats properly. Celiac sprue, pancreatic lipase deficiency and bile salt deficiency are three examples.

Fat and Diet

Fats and oils contain nine calories per gram. Your body will take the extra fatty acids and store them as adipose tissue. That adipose tissue can be broken down and turned into glucose when you need more calories than you consume. This is why counting calories is important for people who want to lose weight and for people who want to gain weight.

The USDA suggests that you get about 30 percent of your calories from fat. For a 2000 calorie per day diet, that would equal 600 calories from fat. Since fat has nine calories per gram, that would be equal to about 67 grams of fat. You should watch your cholesterol and saturated fat intake as well. The USDA suggests no more than 300 mg cholesterol each day, less than 10 percent of your daily calories from saturated fat and less than one percent from trans fats.

A typical western diet often includes much more than that because fats add texture and flavor. Fats also slow down gastric emptying, so high fat meals are more satisfying. Unfortunately, that means too many calories for a lot of people.

Short Chain Fatty Acids

Remember reading about fiber in the carbohydrate lesson? Your body can't digest fiber, which is good for adding bulk to the stool, but fiber has one other important function. The friendly bacteria that live in your colon ferment the fiber and produce short chain fatty acids. Short chain fatty acids have only two to four carbons in their chains. These short chain fatty acids are easily absorbed into the walls of the colon and help to keep the colon tissue healthy and can reduce inflammation. This is important for people with inflammatory bowel diseases who may benefit from adding fiber to their diet to make sure they have enough of these short chain fatty acids in the colon. These fatty acids may also help to prevent colon cancer.

Choosing Healthy Fats

Getting enough fat in the diet is usually not much of a problem, however many people choose too many of the bad saturated and trans fats. You may need to choose more foods with the omega-3 essential fatty acids as well, although most people get enough of the omega-6 essential fatty acids from vegetable oils.

The types of fat you eat have such a big impact on your health. Choose foods with healthy fats and use the right oils and fats for cooking. Here are some healthy and delicious ideas for getting healthy fats:

Eat fish or seafood at least three times per week. The fish should not be fried in batter.
Eat nuts and seeds as snacks. Almonds, walnuts, sunflower seeds and pumpkin seeds are good choices.
Choose canola oil, olive oil and soy bean oil for cooking.
Flax seed oil is high in omega-3 essential fatty acids, but it is not good for cooking. Use flax seed oil cold.

Here are some common foods and their fat content:

One cup low fat milk - 2.4 grams total fat, 1.5 grams saturated fat, 12 mg cholesterol
Three ounces canned tuna - 0.7 grams total fat, 0.2 grams saturated fat, 0.24 g omega-3 EFA, 26 mg cholesterol
One batter-fried chicken leg - 25.5 grams total fat, 6.8 grams saturated fat, 142 grams cholesterol
One ounce (14 halves) walnuts - 18.5 grams total fat, 2.5 grams monounsaturated fat, 13.4 grams polyunsaturated fat
One half cup navy beans - 0.56 grams total fat, 0.3 grams polyunsaturated fat, 0 cholesterol
One broiled sirloin steak - 33 grams total fat, 12.8 grams saturated fat, 248 mg cholesterol
One half cup avocado cubes - 11 grams total fat, 1.6 grams saturated fat, 7.3 grams monounsaturated fat, 0 mg cholesterol
One half cup roasted chicken breast meat - 2.5 grams total fat, 0.71 grams saturated fat, 60 mg cholesterol
Three ounce salmon fillet - 10.5 grams total fat, 2.1 grams saturated fat, 1.8 grams omega-3 EFA, 54 mg cholesterol
One teaspoon flax seeds - 4.3 grams total fat, 2.9 grams omega-3 EFA, 0 mg cholesterol
One three ounce pork chop - 11.1 grams total fat, 4.1 grams saturated fat, 70 mg cholesterol
One piece of apple pie - 19.4 grams total fat, 4.7 grams saturated fat, 5.0 grams polyunsaturated fat, 0 mg cholesterol

Source: USDA National Nutrient Database

This Week’s Assignment

Many people do not get enough omega-3 essential fatty acids from the foods they eat. This week your assignment is to choose a food with some omega-3 essential fatty acids every day. Some examples include a serving of fish, flax seeds, walnuts, pumpkin seeds, canola oil or "omega eggs."

This Week’s Quiz

You can test your knowledge of fats with this quiz: Quiz Three - Fats