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Lecture 
Chapter 5 - Carbohydrates
( On the Syllabus this is listed as Week 7)

Chapter 5 - Carbohydrates

Let's review what we already know about CHOs.
1) On the Nutrition Facts food label, those items dealing with CHOs include: grams of
    Total CHOs and %Daily Value, grams of Dietary Fiber and % DV, grams of Dietary Fiber
    and grams of Sugars. According to the 2,000 kcal diet at the bottom of a food label,
    Total CHO intake should be at least 300 grams/day and Dietary Fiber intake should be
    at least 25 grams/day.
2) The Dietary Goals for Americans states that CHOs should make-up anywhere from
    45-65% of our total kcal intake/day.
3)  In terms of CHOs, The Dietary Guidelines for Americans asks us to choose a variety of
     grains daily, especially whole grains; choose a variety of fruits and vegetables daily;
     choose beverages and foods to moderate our intake of sugars.

Carbohydrates are grouped into two categories: Simple CHOs and Complex CHOs.

Notice that "sugars" end with the suffix "ose".
Notice that "enzymes" end with the suffix "ase".

Lactose Intolerance: an intolerance to dairy sugar, lactose. It is not an allergy. Allergies affect the immune system and involve proteins. Lactose intolerance is an intolerance to dairy sugar, lactose, and does not affect the immune system.

Primary lactose intolerance refers to a loss of enzyme activity not due to a disease. This is common in ~70-80% of the world's population. Lactase levels decrease with age, starting at ~ 2 years of age.

Secondary lactose intolerance develops as a result of a disease condition:
*  an intestinal bacterial infection
*  use of certain medications, especially anti-cancer drugs
*  infections and some drugs can inhibit and interfere with the growth of the rapidly
    reproducing cells of the small intestine where lactase is produced.

Symptoms of lactose intolerance:
*  bloating
*  cramping
*  GI discomfort
What's happening?  Any unabsorbed lactose is metabolized by bacteria in the large intestine into acids and gases. Instead of being metabolized in the small intestine, the undigested lactose continues into the colon to be metabolized by bacteria.

What's a person to do?
*  trial and error with how much lactose can be tolerated
*  no need to avoid all milk products
*  consume a small amount of milk products and take them with other foods"
* fat in a meal slows digestion, leaving more time for lactase action
* eat cheese; much lactose is lost when milk is made into cheese
* eat yogurt: bacteria used to make the yogurt digest lactose
* regarding frozen yogurt, freezing destroys the bacteria's activity
* use Lactaid, a low-lactose milk

Dietary Fiber:
*  food stuff that remains undigested as it enters the colon
*  roughage/bulk are old terms for dietary fiber

Soluble fiber:
*  either dissolves or swells in water (the cooking water in which rolled oats are placed
   will thicken in time due to the soluble fiber of the rolled oats; the same thing happens
   to the cooking water in which legumes are placed; the water will thicken due to the
   soluble fiber of the legumes).
*  can be metabolized (fermented) by bacteria in the colon producing acids and gases
*  found inside and around plant cells
*  examples: pectins, gums

Insoluble fiber:
*  mostly do not dissolve in water
*  not metabolized by bacteria in the colon
*  forms the structural part of plants
*  examples: cellulose, hemicellulose, lignins
*  a cotton ball is an example of cellulose. We don't eat cotton balls, but if we did they'd
    exit in the feces looking the same as when taken by mouth . . . The woody stalk of
    broccoli is made of hemicellulose. The seeds on the outside of a fresh strawberry are
    made of lignin.

Phytic Acid/Phytate:
*  non-nutrient part of plant seeds
*  found in husks of grains, legumes, and seeds
*  can bind minerals such as zinc, iron, calcium, magnesium, copper thus making these
    minerals unavailable for absorption by the body

Recommendations for fiber intake:
*  increase fiber gradually
*  drink lots of fluids
*  get a variety of fiber by eating fruits, vegetables, legumes, whole-grain cereals and
    breads
*  eat 5+ servings of vegetables/legumes/fruits/day
*  eat 6+ servings of grain products/day
*  eat ~20-35 grams of dietary fiber/day from both soluble and insoluble fibers
*  fiber recommendation for children 5 years or older: age + 5 = # grams fiber/day

Health Effects of fiber:
*  Helps with weight control. How? provides satiety; less energy/bite; delays hunger;
   adds bulk to the diet. Studies show that a high-fiber/complex CHO breakfasts led to
   fewer kcals eaten at later meals and snacks compared with those who eat low-fiber or
   high-fat breakfasts.
* Heart disease: high fiber/high complex CHO diet associated with low blood cholesterol
   and decreased risk of heart disease. Why? eating animal products increases the
   consumption of saturated fats; eating vegetable protein increases the intake of soluble
   fiber.
*  Helps prevent cancers: high complex CHO/high fiber diet especially one with green and
   yellow vegetables and citrus fruits protects against some types of cancers. Fiber may
   help prevent colon cancer. How? By diluting, binding, and removing potentially cancer
   causing agents from the colon. This decreases the pH which is associated with
   decreased colon cancer risks.
* helps control diabetes: high fiber foods may decrease the risk of diabetes and/or help
   in the management of diabetes.  How? Soluble fibers delay nutrient transit time through
   GI Tract, so glucose absorption is slowed thus preventing the glucose surge/rebound
   effect.
* GI health: insoluble fiber enlarges the stool providing bulk to the feces. This eases the
   passage of the stool, speeds up transit time, and helps prevent constipation.  Fibers
   prevent hemorrhoids, swelling of the rectal veins.  Fiber stimulates the GI tract muscles
   to prevent diverticula.  It's desirable to have "foot long floaters rather than sinkers".

Excess fiber intake:
*  interferes with mineral absorption
* displaces kcals and nutrient dense foods especially in children and the elderly

CHO Digestion:
Digestion of large CHOs, starches, begins as the starches mix with saliva during the chewing of food. Saliva contains the enzyme, salivary amylase. This enzyme converts starch into a smaller sugar form called maltose. 
Salivary amylase does not work in an acidic environment. So, the stomach's acidity stops further starch digestion by deactivating salivary amylase.

When CHOs reach the small intestine, starch digestion begins again as the pancreas releases pancreatic amylase. The starch is broken down to glucose.

Specialized enzymes are made by the absorptive cells of the small intestine. These enzymes break down the many dietary sugars to single sugar forms. The enzyme sucrase breaks down sucrose to glucose + fructose; the enzyme maltase breaks down maltose to glucose + glucose; the enzyme lactase breaks down lactose to glucose and galactose. 

The single sugars, glucose, fructose, and galactose are absorbed through the villi and travel to the portal vein to the liver.

Fibers travel to the large intestine where some soluble fibers will be metabolized by bacteria. The remainder of the fiber will end up in the feces.

Functions of CHOs in the Body
1)  Energy Production: main function of glucose (and so CHOs in general, since most sugars can eventually yield glucose). The brain derives its energy from glucose. CHOs can also fuel muscle cells and other body cells, but many of these cells usually use fats for their energy needs.

2)  Sparing Protein: CHOs spare protein. Dietary protein can be used to make body tissues and perform other vital processes only when CHO intake is sufficient. If you do not eat enough CHO to yield glucose for red blood cells and the brain, the body is forced to make it from other nutrients such as proteins. This process is called gluconeogenesis; the production of new glucose for the cell. Amino Acids usually provide the carbons for these new glucose molecules. The source of this new glucose must be protein because fats generally cannot be synthesized into glucose.  Amino acids from the proteins in muscle, heart, liver, and kidney tissues, etc. supply the carbons needed to make this glucose. Over time, these organs can become partially weakened.

Generally Americans have more than adequate sources of protein, so sparing protein is not an essential function of CHO. It does become important in some low kcal, low-CHO diets and in semi-starvation situations.

3)  Preventing Ketosis: CHOs are necessary for complete fat metabolism. "Fat burns in a fire of CHO". Insufficient CHO intake leads to an incomplete breakdown of fats in the metabolic pathways. Without sufficient dietary CHO, carbon dioxide and water molecules are not readily formed during fat metabolism. Instead fats mostly become ketones. The liver is the major organ that produces these ketones. Ketones are incomplete breakdown products of fat metabolism. Acetoacetic acid, betahydroxybutyric acid, and acetone are examples of ketones. 
We need to consume ~ 50-100 grams of CHO/day to ensure complete fat metabolism and to avoid ketosis.  We usually consume 200+ grams of CHO/day.

In starvation conditions, people do not eat enough CHOs and so ketones soon appear in their bloodstream. This is a normal metabolic response. Part of the brain and other tissues (heart and skeletal muscles) use these ketones for fuel. This is an important adaptation measure for survival during starvation; it reduces protein breakdown by about 1/3.

In untreated Type I Diabetes, ketones can be formed, partly because there is not enough insulin to allow for normal glucose metabolism.

When the liver produces more ketones than peripheral tissues can oxidize, the level of ketones in the blood can reach toxic levels, resulting in ketosis. This lowers the pH of the body leading to metabolic acidosis.

Ketosis and metabolic acidosis occurs in:
* starvation situations, including anorexia nervosa
* fasting
* low-CHO diets
* uncontrolled diabetes

4)  Glucose can be stored as glycogen.  When blood glucose falls, the liver cells release the glucose from glycogen making it available to supply energy to the central nervous system and other organs.

5) Glucose can be converted to fat. When the body has more glucose than it can use, it can be converted to and stored as fat.

Blood Glucose Regulation
To function optimally, the body must maintain blood glucose within limits that permit the cells to be nourished. Normal blood glucose is ~80-120 mg/dL. If blood glucose falls below this level a person would experience hypoglycemia (low blood sugar). If blood glucose is consistently above normal a person would have hyperglycemia (high blood sugar-diabetes)
Blood glucose homeostasis is regulated mainly by two hormones: insulin and glucagon; both are produced by the pancreas. Insulin moves glucose from the blood into the cells. Glucagon brings glucose out of storage when blood glucose levels are low. Glycogen is the storage form of glucose.

Another hormone, epinephrine, can also cause the liver to release glucose into the bloodstream. Epinephrine is the "fight or flight" hormone which ensures the body cells will have energy fuel in emergencies.

Eating balanced meals helps the body maintain a balanced blood glucose level. Balanced meals contain complex CHOs, fibers, protein, and a little fat. The fibers and fat slow down digestion and absorption of CHOs, so glucose enters the blood stream gradually, providing a steady, ongoing supply. Dietary protein causes the secretion of glucagon, whose effects are opposite from those of insulin, helping to maintain blood glucose within the normal range. 

In some people, blood glucose regulation fails. They end up with hypoglycemia or diabetes. They plan their diets to help maintain their blood glucose within a normal range.

In diabetes, the blood glucose stays high after a meal because insulin is either inadequate or ineffective. Dietary CHOs do not cause diabetes.
There are two main types of diabetes: In type 1 diabetes the pancreas does not make insulin. In type 2 diabetes, the cells fail to respond to insulin.

Hypoglycemia: blood glucose drops quickly after eating. The symptoms include weakness, sweating, anxiety, sleepiness, irritability, hunger, etc.  The symptoms can usually be controlled by eating 5-6 small meals ( each containing complex CHOs, fiber, protein, a small amount of fat) through the day. 

Glycemic Effect: refers to the way blood glucose responds to foods: how quickly glucose is absorbed after a person eats, how high blood glucose rises, and how quickly it returns to normal.  See Table 5-7 on page 182 "Glycemic Index & Glycemic Load of Common Foods".  A low glycemic effect is desirable. Why? These foods allow for slow absorption, a modest rise in blood glucose, and a gradual return to normal. There's controversy regarding the practical application of the glycemic index. It could help those who have hypoglycemia or diabetes but it isn't a panacea.

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Study Guide
The following is for your use. You will not submit your responses to the instructor.

Chapter 5 - The Carbohydrates: Sugars, Starches, and Fibers
1. What is the primary fuel for the brain? What is the storage form of glucose? What
    foods provide CHOs?

2. What is the basic chemical formula for a simple CHO (monosaccharide)?

3.  List the simple CHOs. Name the monosaccharides. What is the significance of glucose
    to nutrition? What monosaccharide is the sweetest? What foods contain fructose?

4.  What does the term disaccharide mean? What is the common component of all
    disaccharides? What is the chemical reaction needed to made a disaccharide? What is
    the chemical reaction needed to take apart a disaccharide? Name the disaccharides.
    What is the most familiar disaccharide? What monosaccharide is found in milk sugar?
    What is the principal disaccharide found in milk sugar?

5. What does the term polysaccharide mean? What three complex CHOs are important in
    nutrition? What is the storage form of glucose in animals? What is the storage form of
    glucose in plants? Where is glycogen stored in the human body? What are the richest
    food sources of starch?

6. What is the ultimate goal of CHO digestion and absorption? Where does starch
    digestion begin? What is the enzyme responsible for beginning starch digestion? What
    happens to starch digestion in the stomach? Where does most CHO digestion occur?
    What major CHO-digesting enzyme is responsible for further digesting polysaccharides
    to disaccharides and short glucose chains? Name the enzymes that dismantle the
    following disaccharides: maltose, sucrose, lactose. What do all disaccharides
    contribute to the body after they are dismantled? After absorption occurs, what organ
    is responsible for converting fructose and galactose to glucose? What remains in the
    digestive tract after all sugars and most starches are digested? What is the function
    of resistant starch? Where does most nutrient absorption take place?

7. What enzyme is absent or deficient in people suffering from lactose intolerance? What
    is the effect of aging on lactase activity? What percent of the population retain
    enough lactase to digest and absorb lactose efficiently? What are the symptoms and
    causes of lactose intolerance? What populations have the lowest and highest
    prevalence of lactose intolerance? How can lactose intolerance be managed?

8. What is the primary role of CHO in human nutrition? What is the function of the liver in
    CHO metabolism, and how does it respond to low blood glucose? How much of the
    body's total glycogen is stored in the liver and muscles?

9. Define gluconeogenesis and protein-sparing action. Under what circumstances are
    ketone bodies formed? How much dietary CHO is necessary to spare body protein and
    prevent ketosis? What happens to glucose that is not used for immediate energy or
    converted to glycogen?

10. What is homeostasis? What can happen if blood glucose fluctuates to the
     extremes-either high or low? What are the two main regulatory hormones that control
     blood glucose concentrations? Summarize the steps involved in blood glucose
     regulation. How does epinephrine function in blood glucose
     regulation? What are two conditions that can result when blood glucose regulation
     fails? Define hypoglycemia. What is the "glycemic effect" of food? Briefly explain the
     controversy surrounding the usefulness of the glycemic index.

11. How many pounds of added sugar does the average person consume per year? What
     is the recommended sugar intake based on a percentage of total kcal per day? Briefly
     describe two ways in which excessive sugar intake can be detrimental to people.
     Explain whether research supports the accusations that excessive sugar intakes
     cause obesity, heart disease, and hyperactivity.

12. Describe the health effects of complex CHOs on the following: weight control, heart
     disease, cancer, and diabetes. What is the recommended intake of CHO as a
     percentage of total energy? What is the number of servings recommended by the
     MyPyramid to help a person meet daily complex CHO needs?

Fill in the blanks to follow CHO through the GI tract, through absorption, and through metabolism.
1. Starch digestion begins in the  ____ with a salivary enzyme known as ____.
2. Hydrolysis of starch in the stomach is stopped due to the action of ___ and ___.
3. Starch digestion continues in the ___ after it leaves the stomach.
4. Maltase hydrolyzes the disaccharide known as ____.
5. Sucrase hydrolyzes the disaccharide known as ____.
6. Lactase hydrolyzes the disaccharide known as ____.
7. The large intestine contains indigestible CHOs known as ____ and ____ that are not digested by human enzymes, but that are digested by ____.
8. Absorption occurs primarily in the ____.
9.  Some glucose absorption occurs in the ____.
10.  Absorbed monosaccharides inter the blood, go to the liver, and are converted to ____.
11. The main energy source for the brain, nerve cells, and blood cells is ____.
12. ____ (fractional amount) of the body's total glycogen is stored in the liver.
13. ____ (fractional amount) of the body's total glycogen is stored in the muscles.
14. The organ that dismantles glycogen to glucose for export into the blood is the ____.
15. The making of glucose from non-CHO sources such as body protein is known as ____.
16. _____ spares protein from gluconeogenesis and prevents ketosis.
17. We need at least ____ g CHO per day to prevent ketosis and excessive breakdown of body protein.
18. Some glucose not used for immediate energy is stored as ____.
19. Excess glucose not stored as glycogen is converted to ____.

1. What is fiber? What are the major non-starch polysaccharides? What is the main
    difference between starch and fiber with regard to their bonds? Define the following
    terms: cellulose, hemicellulose, pectins, gums, mucilages, and lignin.

2. How do soluble fibers affect the body? How do insoluble fibers affect the body? 

3. What is phytic acid? What might be the impact of a high-fiber diet on minerals in the
    body?

4. What is the effect of fiber in the stomach during digestion? What is the function of
    fiber in the large intestine? What is the effect of bacteria on fiber? What is the energy
    contribution of fiber?

5. How can fiber impact weight control? How do foods rich in soluble fiber lower blood
    cholesterol, thus reducing the risk for heart disease? Explain how a high-fiber diet may
    protect against colon cancer. What effect do soluble fibers have on diabetes with
    regard to glucose absorption? Explain how dietary fibers enhance the health of the
    large intestine with regard to the following: stool size and passage, transit time,
    constipation, water intake, hemorrhoids, and diverticula.

6. How can too  much fiber affect a person with a small stomach capacity? What
    symptoms are associated with increasing fiber too quickly? What steps can be taken
    to prevent complications associated with increased fiber intake?

7. According to the American Dietetic Association, what is the recommended intake of
    fiber per day? What is the average daily fiber intake for people in the USA? What foods
    and what number of servings from the Food Guide Pyramid will ensure an adequate
    supply of fiber each day? List 3 health claims concerning fiber on food labels
    authorized by the FDA.

8. Define artificial sweeteners? What are sugar alcohols? What is the ADI? Which artificial
    sweeteners are approved by the FDA?

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