After you have completed your study of this chapter, you should have acquired the following knowledge and skills.  You should be able to:

• Explain the way lipids are useful, both in foods and in the body.
• Describe the structure of a triglyceride noting the differences between saturated and unsaturated fats.
• Summarize the processes of lipid digestion, absorption, transport, and utilization in the body, Including the significance of the lipoproteins.
• Explain why manufacturers frequently hydrogenate fats and the possible health implications of consuming the trans-fatty acids formed during hydrogenation.
• List the arguments for and against the growing use of the fat replacers Simplesse and olestra.
• Plan a diet containing fat in the proper proportions and in the recommended amounts to provide optimal health and pleasure in eating.
• Discuss the possible roles of high-fat diets in the causation of obesity.

Triglycerides are the most common lipids (what we call fat) and comprise approximately 95% of dietary fat. Triglycerides are used for energy and stored in the body's fat cells. This energy source has twice the calories of Carbohydrate or Protein.

Other Lipids - The remainder of dietary fat is found mostly in two other classes of compounds listed below.

phospholipids -structural relatives of triglycerides made by substituting a polar phosphate group for one of the terminal fatty acids in a triglyceride making the structure amphiphilic (or a good emulsifier).

sterol - heterocyclic ring compounds that have no relationship to triglyceride structure. These are lipids because of solubility considerations only and include Vitamin D, steroid hormones and bile.  These compounds are necessary for proper health and are derived from cholesterol.  This is an example of the positive role cholesterol plays in our body (and why our bodies synthesize cholesterol).

Solubility
Oil and water separate; fat-soluble compounds stay dissolved in the oil and water-soluble compounds stay dissolved in water.  The process of mixing fats with water is called Emulsification.   Emulsifiers  have a hydrophilic (fatty acid with phosphate group) and hydrophobic (regular fatty acid) ends. Emulsifiers help solubilize hydrophobic molecules. Both phospholipids and bile act as emulsifyers.

Flavor
Many of the flavors we enjoy in food are due to lipid soluble chemicals in fats and oils. It is no surprise that Fats and Oils taste good. So good in fact that many of us eat too much of these!

Much controversy shrouds the truth about fatty acids and health.  We must keep in mind that too much fat is not good for us. High fat diets have been linked to cardiovascular disease, some types of cancer, and other degenerative diseases.

• Provide essential fatty acids
• Provide concentrated food energy
• Carry fat soluble vitamins
• Provide raw materials for synthesis
• Stimulate appetite, provide satiety

Fats in the Body

• Chief form of stored energy in the body (1 pound of fat = 3500 Kcal)
• Provide energy to do work
• Serve as emergency fuel in hard times
• Fat pads protect organs from shock
• Insulate against the cold
• Major component of cell membranes
• Converted to other compounds on demand
  

Normal Blood Lipid Levels
Total Cholesterol < 200 mg/dL
Total Triglycerides < 200 mg/dL
LDL < 130 mg/dL
HDL > 35 mg/dL

What does food cholesterol have to do with blood cholesterol?

Food Cholesterol has minor influence on blood cholesterol in most humans!
Blood Cholesterol level is much more related to amount of fat in diet.
See lecture clips in left margin for the National Cholesterol Education Program (NCEP) Recommendations

Fat transport in blood requires cholesterol containing lipoproteins. Reducing dietary fat intake can decrease the need for the body to synthesize cholesterol for dietary fat transport.

• High levels of LDL in blood is one of the big risk factors for cardiovascular disease.
• High levels of HDL in blood is associated with a low risk of heart attacks. To raise HDL’s, exercise more, lose weight and stop smoking.

See Table 5 - 2 for recommendations about dietary fat intake.

 

Obesity is often a risk factor associated with disease, and obesity itself is considered a disease.  A person wishing to reduce the amount of stored fat in their body is more likely to be successful when following a moderate weight-loss plan.  One pound of fat is the equivalent of 3500 Calories.  If a person reduced their Calorie intake by 500 each day, that person could loose one pound of fat per week (500 x 7 = 3500).  Some folks fall in the trap of thinking more Calorie restriction is better, which is not true.  Our bodies have an incredible ability to adapt to events and surroundings to ensure effeciency. A rapid and big reduction in Calorie intake will most likely lead to "starvation mode" which initiates many mechanisms including catabolism of visceral protein.  Catabolism of protein is followed by diuresis to eliminate the urea.  The resulting weight loss is mostly lean tissue and water......these are two components that you do not want to loose.
Weight control is covered in more detail in Chapter 9.

WOW® Potato Chips from Frito Lay are the latest low fat product made using olestra.  Most people that try these chips have no digestion problems, however, excessive intake of the chips have led to "anal leakage".  Another complaint about this product is that the mouth "feel" is not the same.

These products try to mimic texture and flavor, but they are not without problems and side effects in some people.

Benecol, a new product approved May 17, 1999 by FDA, is a margarine containing plant stanol ester that has the effect of lowering blood cholesterol levels.  This product was first produced in Finland and has been sold there since 1995.

Xenical is a prescription drug that prevents absorption of nearly a third of fat consumed.  This product was approved April 26, 1999 by FDA, is intended for the clinically obese and not just dieters.

cis and trans fatty acid double bonds are found in unsaturated fatty acids, but only the cis forms are natural and usable by the body.

Trans fatty acids occur minimally in nature and abundantly in processed foods. Trans fatty acids are the result of hydrogenation and cause an increase in LDL cholesterol and decrease in HDL cholesterol, which increases the risk of heart disease.

Some cis fatty acids are converted to trans during hydrogenation, hence the concern that hydrogenated oils are less healthful than 'natural' oils.

Below are portion sizes (not serving sizes)

• teaspoon oil or shortening
• 1 1/2 teaspoon mayonnaise, butter or margarine
• 1 tablespoon regular salad dressing, cream cheese, or heavy cream
• 1 1/2 tablespoon sour cream

Meats, Poultry, Fish, Dry Beans, Eggs, and Nuts Group - a serving size is 3 oz.

One oz. lean (free of visible fat) meat has 3 g fat [10%]
One oz. medium (some visible fat) meat has 5 g fat [20%]
One oz. High fat (plenty of visible fat) meat has 8 g fat [30%]

Milk, Yogurt, and Cheese group -

Cheese is @ 1/3 fat, Standard milk is 3.2% fat, lower fat milks are popular.
Ice Cream, cakes and cookies are high. Candy is very high in saturated fat.

Bread, Cereal, Rice, and Pasta Group -

Cereal products can be low in fat.
Baked goods often have high amounts of hidden fat.
Fried foods (most fast foods) are loaded with extra fat.
Potato chips, popcorn, corn chips, etc. are high in undesirable saturated fat.
Look at a Potato Chip bag Nutrition Facts label. You will find that over 60% of the calories in potato chips come from fat, and most of that will be saturated.

Examine the information in Figure 5-19. This will help you to understand how you can start now to reduce the amount of fat in your diet.

Total fat, saturated fat, cholesterol and calories from fat for a serving of food are required on all food labels. Be careful! Don’t forget to check the serving size, it may be a fraction of what you consider a serving.

The fat components listed on food labels are listed in grams and in % Daily Values. The definition of the %DV is described near the bottom of the label and the gram values for both a 2000 Calorie and 2500 Calorie diet are listed.

See Chapter 2 about reading food labels