Fat In The Body



Fat In The Body

How Fat Is Digested

Dietary fats, like those in butter, meat or cooking oils, are basically organic compounds composed of carbon, hydrogen, and oxygen. They consist of complex molecules and are the most highly concentrated source of energy in our daily diet. They belong to a class of substances called lipids. Unfortunately, dietary fats do not dissolve in water, and as a result they are not easily broken down by fat-digesting enzymes (lipase) in the watery content of the intestinal tract. Thus fats tend to take longer to digest than carbohydrates or proteins.

Although a small amount of lipase is secreted from the tongue and by the stomach, these digestive actions are not significant, as almost no real breakdown of fat occurs until the fats reach the small intestine in the form of chyme.

Fat Breakdown in the Small Intestine

Fat digestion and absorption requires that the complex fat molecules be broken down into smaller more manageable molecules. This is done by mixing the fat with the digestive enzyme lipase, which enters the small intestine from the pancreas.  This enzyme is the main source of enzymes for digesting fats and proteins. Lipase chops up lipid molecules into fatty acid molecules and glycerol molecules. However, because fat does not dissolve in water, the fat molecules enter the small intestine in a large mass, which makes it impossible for the pancreatic lipase enzymes to attack them, since lipase is a water soluble enzyme and can only attack the surface of the fat molecules. To overcome this problem the digestive system uses a substance called bile, produced in the liver but stored in the gallbladder, which enters the small intestine via the bile duct. Bile emulsifies fats - meaning, it disperses them into small droplets which then become suspended in the watery contents of the digestive tract. Emulsification allows lipase to gain easier access to the fat molecules and thus accelerates their breakdown and digestion.

How Fat Is Digested and Absorbed Into the Bloodstream

Lipase and other digestive juices break down the fat molecules into fatty acids and types of glycerol. Absorption of fat into the body, which takes 10-15 minutes, occurs in the villi - the millions of finger-like projections which cover the walls of the small intestine. Inside each villus is a series of vessels that absorb the fatty acids and glycerol and eventually drains them into the bloodstream. The fatty acids are transported via the bloodstream to the membranes of adipose cells or muscle cells, where they are either stored or oxidized for energy. Since glucose rather than fat is the body's preferred source of energy, and since only about 5 percent of absorbed fat (the glycerols) can be converted into glucose, a significant proportion of digested fat is typically stored as body fat in the adipose cells. The glycerol part is absorbed by the liver and is either converted into glucose and/or used to help breakdown glucose into energy.

Fat Replacer

 

Fat replacers, also called fat substitutes, are substances that take the place of all or some of the fat in a food and yet give the food a taste, texture, and mouth feel similar to the original full-fat food.

 

Fat replacers serve two purposes. They reduce the amount of fat in food, and they usually reduce the calorie content of the food.

 

Fat is not a single substance, but a collection of different compounds that are all made of a glycerol molecule and three varying fatty acids. Fat is a necessary part of a healthy diet. It provides essential fatty acids, helps regulate cholesterol metabolism, carries fat-soluble vitamins throughout the body, and provides nine calories of energy per gram.

 

Although there is no official recommended daily allowance (RDA) for fat, the American Heart Association strongly recommends that fats provide no more than 30% of one’s total daily calories. The average American gets about 34% of his or her calories from fat (down from about 41% in the 1950s).

 

As of 2000, there were more than 5,000 reduced-fat foods on the market. New reduced- and low-fat foods were being introduced at the rate of about 1,000 per year. Concern about heart disease, obesity, diabetes, and their relationship to diet has turned processed foods containing fat replacers into a multi-billion dollar industry.

 

To be labelled ‘low fat’ a product must contain 3 g of fat or less per serving. To be labelled ‘reduced fat’ or ‘reduced calorie,’ a product must contain 25% less fat or 25% fewer calories than the regular version of the product. ‘Light’ foods contain half the fat or one-third the calories of the regular product. ‘Fat-free’ means the food has less than 0.5 g of fat per serving. Fat enhances food flavour, adds volume, and gives food a particular texture and mouth feel. Removing fat from food usually results in unappealing, unmarketable products. To achieve fat and calorie reduction, processors have turned to fat replacers.

 

Types of fat replacers

 

Fat replacers are either carbohydrate-based, protein-based, or fat-based. Most foods use several different fat replacers that come from different sources. Many are substances that have been found in foods for years, but are now being used in different ways.

 

Carbohydrate-based fat substitutes have the creaminess of fat. They absorb water, add volume, thicken, and stabilize foods. They are used in baked goods, frozen desserts, yogurts, cheeses, sour cream, low-fat puddings, processed meats, salad dressings, sauces, and spreads. Because fat contains nine kcalories per gram and carbohydrates contain only four calories per gram, every gram of fat replaced with a gram of a carbohydrate-based fat substitute reduces the calorie content of the food by five calories as well as reducing the fat content. Carbohydrate-based fat replacers cannot be used in frying.

 

Protein-based fat replacers are made from milk protein and/or egg white protein. They have the same mouth feel as fats. Like carbohydrate-based substitutes, protein provides four calories per gram so they reduce the calorie content of food by five calories per gram of fat replaced. Protein-based fat replacers are used in butter, cheese, frozen dairy desserts, mayonnaise, soups, salad dressings, and sour cream. They do not work well in baked goods and cannot be used for frying.

 

Fat-based fat replacers are made of fat molecules that are modified so that they cannot be absorbed or can be only partially absorbed in the intestine. Olestra, now marketed under the name Olean, is the best known of these products. Olestra is made of six to eight fatty acids bound to a sucrose (sugar) molecule. Normal fats have only three fatty acids. Adding the extra fatty acids makes the olestra molecule too large to be absorbed, so it simply passes through the intestine and is eliminated as waste. In this way, it adds no calories to food. Proctor & Gamble spent 25 years and more than $200 million developing this fat replacement.  Olestra has all the properties of regular fat and can be used in frying. It is used mainly in crunchy snack foods such as potato chips. Other fat-based fat replacers are partially absorbed by the body and contain about five calories per gram.

 

Cholesterol

 

Cholesterol is a sterol (one of the categories of lipids) meaning it is a fatty alcohol made from glucose or saturated fatty acids.  It is a waxy substance produced by the liver and found in certain foods. It is needed to make vitamin D and some hormones, build cell walls, and create bile salts that help you digest fat. Your liver produces about 1,000 milligrams of cholesterol a day, enough cholesterol so that if you never touched another cheese fry, you'd be OK. But it's hard to avoid cholesterol entirely because so many foods contain it.  You probably consume about 150 to 250 milligrams in the foods you eat.

 

Too much cholesterol in the body can lead to serious problems like heart disease. Many factors can contribute to high cholesterol, but the good news is there are things you can do to control them.

 

Lipids are fats that are found throughout the body. Cholesterol, a type of lipid, is found in foods from animal sources. This means that eggs, meats, and whole-fat dairy products (including milk, cheese, and ice cream) are loaded with cholesterol — and vegetables, fruits, and grains contain none.

 

Because cholesterol can't travel alone through the bloodstream, it has to combine with certain proteins. These proteins act like trucks, picking up the cholesterol and transporting it to different parts of the body. When this happens, the cholesterol and protein form a lipoprotein together.

The two most important types of lipoproteins are high-density lipoproteins (or HDL) and low-density lipoproteins (or LDL). You've probably heard people call LDL cholesterol "bad cholesterol" and HDL cholesterol "good cholesterol" because of their very different effects on the body. Most cholesterol is LDL cholesterol, and this is the kind that's most likely to clog the blood vessels, keeping blood from flowing through the body the way it should.  LDL cholesterol transports cholesterol from the liver to other tissues. They carry about 75% of the cholesterol in blood.

 

On the other hand, HDL cholesterol removes cholesterol from the blood vessels and carries it back to the liver, where it can be processed and sent out of the body.

 

Why Do People Worry About High Cholesterol?

 

When you have too much cholesterol, it can be dangerous to your health. When LDL cholesterol levels are high, cholesterol is deposited on the walls of arteries and forms a hard substance called plaque. Over time, plaque causes the arteries to become narrower, decreasing blood flow and causing a condition called atherosclerosis, or hardening of the arteries.

 

When atherosclerosis affects the coronary arteries (the blood vessels that supply the muscles of the heart), the condition is called coronary artery disease, which puts a person at risk for having a heart attack. When atherosclerosis affects the blood vessels that supply the brain, the condition is called cerebral vascular disease, which puts a person at risk of having a stroke.

Atherosclerosis may also block blood flow to other vital organs, including the kidneys and intestines. This is why it's so important to start paying attention to cholesterol levels as young as you can so that you can delay or prevent serious health problems in the future.

Information adapted from:







Analysis Questions:

Answer the following questions on a separate sheet of paper.  These will help you understand the information presented in the article. Please pass these in at the end of class and make sure your name is on it!

1. Why do fats take longer to break down in the body than carbohydrates?

2. Where does the breakdown of fats mechanically begin? Where does it chemically begin?

3. What is the first step of fat digestion in the small intestine and how is it accomplished?

4. What role does bile play in fat digestion?

5. How are fats absorbed into the bloodstream? Where do they go once absorbed?

6. What is a fat replacer?

7. What is the purpose of a fat replacer?

8. Why is the demand for fat replacers and lower fat foods rising in the past few years?

9. Explain how foods can obtain the following labels:

• Low fat

• Reduced fat or reduced calorie

• Light

• Fat free

10. What is a carbohydrate-based fat substitute? What benefits does it bring? What foods are it used in?

11. What is a protein-based fat substitute? What benefits does it bring? What foods are it used in?

12. What is a fat-based fat substitute?  What benefits does it bring? What foods are it used in? What are some health drawbacks of this type of fat substitute?

13. What is cholesterol? What foods contain cholesterol?

14. What do HDL and LDL stand for? What is the difference between them?

15. What can happen when your body contains too much cholesterol?

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