Carbohydrates and Human Health

• This document outlines the function of carbohydrates in human health with textbook section, figure, and page numbers from chapter 4 provided.
• The six sections are:
  • Chemistry of Carbohydrates
  • Carbohydrates in Foods
  • Digestion, Absorption, and Metabolism
  • Blood Glucose Regulation and Diabetes
  • Carbohydrates & Health
  • Non-nutritive Sweeteners

Chemistry of Carbohydrates

• Describes the chemistry of carbohydrates
• One should be able to:
  • Identify the monosaccharides in sucrose, lactose and maltose
  • Distinguish between hydrolysis and condensation
  • Explain the differences between digestible and indigestible polysaccharides
  • Describe the two categories of total fibre
  • Distinguish between soluble and insoluble fibre
  • Explain the differences between glycogen, amylopectin, and amylose

Photosynthesis

• Plants biosynthesize glucose using the energy from sunlight.
• Energy from sunlight is used to convert carbon dioxide and water to the monosaccharide glucose.
• Glucose can then be converted to starch:
  • A polymer of glucose (polysaccharide)
  • Other monosaccharides, disaccharides, and polysaccharides

Monosaccharides

• Many monosaccharides exist
• Glucose, fructose, and galactose are the common ones

Disaccharides

• Two monosaccharide units covalently bonded.
• Maltose contains 2 glucose units.
• Lactose contains 1 galactose and 1 glucose unit.
• Sucrose contains 1 glucose and 1 fructose unit.

Hydrolysis

• Hydrolysis: breaks down the linkage or covalent bond between sugars with the addition of water.

Condensation

• Condensation: forms a linkage or covalent bond between sugars with the release of water.

Oligosaccharides

• Contain 3 to 10 monosaccharide units.
• They are commonly found in beans.
• Fermentation of oligosaccharides in the colon can cause flatulence.

Polysaccharides

• Contain more than 10 monosaccharide units
• Digestible:
• Starches (amylose, amylopectin)
• These are broken down by digestive enzymes and absorbed
• Indigestible:
• Dietary fibre
• Resistant starch
• These cannot be broken down by digestive enzymes

Total Fibre

• Dietary Fibre: Fibre in intact foods
• Functional Fibre: Fibre isolated from plant sources
• Both dietary fibre and functional fibre can be a mixture of:
  • Insoluble fibre: which does not dissolve in water
  • Soluble fibre: which absorbs water and can form viscous solutions

Polysaccharides of Glucose

• Glycogen: polysaccharide stored in the liver and muscle
• Amylopectin: branched polysaccharide
• Amylose: linear polysaccharide
• Cellulose: An example of dietary fibre:
• Other forms of dietary fibre are composed of other monosaccharides beside glucose

Carbohydrates in Foods

• The chemical composition of carbohydrates, this section looks at carbohydrates in foods. It will
  • Distinguish between unrefined and refined carbohydrates
  • Define "free sugars"
  • Explain the importance of the comparison made between a kiwi and a soft drink
  • Describe the three major components of a kernel of whole grain
  • Explain how 100% whole grain bread differs from 100% whole wheat bread

Unrefined vs Refined Carbohydrates

• Carbohydrates are categorized as either "unrefined" or "refined".
• Unrefined Carbohydrates:
• Whole foods like fruits, vegetables, whole grains, and legumes (beans, peas, lentils)
• Refined Carbohydrates:
  • Carbohydrates as ingredients in highly processed foods like white flour, and starches like cornstarch and potato starch
• Free sugars:
  • Not inside cells of food, easy absorbed
• Added sugars:
  • Monosaccharides and disaccharides added during processing e.g. glucose, fructose, sucrose
• Monosaccharides and disaccharides in honey, syrups, juices

Total Sugars

• Total sugars include sugars intrinsic to food, like the sugars in fruits, and free sugars.

Free Sugars

• The many names for sugars, from monosaccharides or disaccharides:
• Sugar (sucrose)
• Invert sugar (1:1 mixture of glucose and fructose)
• Glucose
• Dextrose (same as glucose)
• Maltose or malt sugar
• Lactose
• Corn syrup (glucose in syrup form)
• Honey
• Molasses
• Fruit juice concentrates
• Glucose/fructose or high fructose corn syrup (a mixture of glucose and fructose in syrup form)

Nutrient Density

• A sugar-containing kiwi is compared with a soft drink.
• Both have similar kcalorie and sugar content, but the kiwi is much more nutrient-dense
• It contains fibre, potassium, vitamin C and other nutrients.
• The soft drink provides nothing but kcalories.
• Canada's Food Guide recommends drinking water and eating fresh fruit.

Whole Grains

• Whole grain refers to the entire kernel of cereal:
• Endosperm, bran, and germ
• Pseudocereals: Not technically grains, but are nutritionally similar and consumed like grains
• Food products that contain whole grains can voluntarily put a stamp on their label to signal consumers that the product contains whole grains.
• The 100% stamp is the better option

Bread

• 100% Whole Grain Wheat Bread
  • Made from flour that contains the whole grain:
    • Endosperm (contains starch)
    • Bran (contains fibre)
    • Germ (contains vitamin E and fat)
• 100% Whole Wheat Bread
  • Made from flour that contains:
    • Endosperm
    • Bran
• Germ is removed because it contains oil and spoils easily
• Some nutrients are missing, as a result of missing germ, but still a good source of fibre
• White Bread
  • Made from white flour that contains endosperm only; bran and germ removed
• Fortified with iron, thiamin, niacin, riboflavin to replace some but not all nutrients removed when bran and germ removed
  • Low in fibre and vitamin E

Fibre and Canadians

• Adequate Intake (AI) for dietary fibre is an Al is assigned to a nutrient when there is not enough research to determine an EAR.
• If 50% or more of the population is consuming above the Al, the population intake is adequate.
• If less than 50% of the population is consuming above the Al, the population intake may or may not be adequate.
• Results suggest that adult Canadians' intake of fibre may or may not be adequate, as less than 50% are consuming above the Al, in all age categories shown.

Digestion, Absorption, and Metabolism of Carbohydrates

• After looking at the types of carbohydrates and carbohydrate-containing foods that Canadians eat, the digestion, absorption, and metabolism are explained.
• One should be able to:
  • Distinguish between the functions of salivary amylase and pancreatic amylases
  • Explain how lactose intolerance develops
  • Describe how both soluble and insoluble fibre reduces constipation
  • Describe how soluble fibre slows the absorption of nutrients
  • Explain cellular respiration and list the four major steps in the metabolism of glucose and the formation of ATP

Carbohydrate Digestion

• Mouth: The enzyme salivary amylase starts breaking starch into shorter polysaccharides.
• Stomach: Salivary amylase is inactivated by acid, so no carbohydrate digestion occurs.
• Small Intestine: Starch digestion and breakdown of disaccharides occur.
  • Pancreatic amylases continue breaking down starch into monosaccharides, disaccharides, and oligosaccharides.
  • Enzymes attached to the brush border of the small intestinal villi complete the digestion of carbohydrates.
  • Disaccharides and oligosaccharides are broken down into monosaccharides.
• Large Intestine: Fibre and other indigestible carbohydrates are partially broken down by bacteria to form short chain fatty acids and gas. Some fibre is excreted in the feces.

Brush Border Enzymes Include

• Breaks down: - Sucrase- sucrose into fructose and glucose - Maltase- maltose into 2 glucose - Lactase- lactose into galactose and glucose
• Infants produce lactase to process lactose in human milk; Many lose this ability with age, leading to lactose intolerance

Lactose Intolerance

• Undigested lactose enters the colon, where it is fermented by microflora, causing intestinal gas and bloating.
• Varies in severity
  • many can tolerate lactose in small quantities or in fermented milk products

Indigestible Carbohydrates

• Insoluable Fibre:
  • Does not dissolve in water
  • Not fermentable by microflora
  • Increases fecal bulk promotes Gl motility reduced constipation
  • Sources are bran-containing and whole-grain foods -Soluble Fibre:
  • Is fermented by microflora to short chain fatty acids
  • Absorbs water softens fecal bulk reduced constipation
  • sources include psyllium-containing foods

Role of Fibre

• Dietary fibre: especially soluble fibre
  • dilutes the contents of the stomach and small intestine
  • slows the absorption of nutrients
• Reduces blood glucose levels

Glucose Metabolism

• After absorption, glucose goes to cells in the body, to be used a source of energy.
• Is broken down to carbon dioxide and water In the presence of oxygen, this happens with the associated production of ATP(adenosine triphosphate).
• This process is called cellular respiration

Glucose Metabolism Process

• Glycolysis: splits glucose, a 6-carbon molecule, into two molecules of pyruvate, a 3-carbon molecule This step produces high-energy electrons and a small amount of ATP. After that
  • pyruvate either breaks down to produce more ATP or used to make glucose via gluconeogenesis.
• Citric Acid Cycle: When oxygen is available, pyruvate can be used to produce more ATP.
• Remove one carbon as carbon dioxide, producing a 2-carbon molecule which combines with coenzyme A to become acetyl-CoA releases high-energy electrons. Each acetyl-CoA enters into the citric acid cycle reacts with 4-carbon compound, oxaloacetate, to produce citric acid. From citric acid 2 carbons are lost as carbon dioxide, high-energy electrons are released, and a small amount of ATP is produced. In the final step, the electron transport chain accepts the high-energy electrons released in previous steps and uses the energy to synthesize ATP. The electrons become combined with oxygen and hydrogen to form water.

Glyconeogenesis

• When blood glucose levels drop, protein is broken down.
• Some of the amino acids in protein are glucogenic, meaning they can be converted to glucose
  • This process called gluconeogenesis.

Ketone Formation

• When carbohydrates (and hence oxaloacetate) is present, acetyl Co-A, from the breakdown of fatty acids can enter the citric acid cycle.
• When carbohydrate intake is low or absent like during fasting acetyl Co-A cannot enter the citric acid cycle, and is diverted into metabolic pathways that produce ketones.

Blood Glucose Response

• Shown are the glucose response curves.
• The rise in blood glucose is more rapid in the absence of soluble-fibre.
• The steep rise stimulates the release of high levels of insulin which in turn causes the large drop in blood glucose
• In a fibre rich meal (blue line) the rise was not as high, so less insulin is released and the decline is more gradual.
• The gradual response is the healthier choice because it does not stress the pancreas

Glycemic Index

• Glycemic response is more blunted in a high soluble-fibre rich meal.
• Foods high in soluble fibre absorbs water and form a viscous solution that dilutes glucose.
• This slows the release of glucose from the food in the digestive tract and into the blood.
• Is characterized by the glycemic index.

Definition of Glycemic Index

• Ranking of the effect, on blood glucose, of a food of a certain carbohydrate content relative to an equal amount of carbohydrate
• Usually 50g of glucose or white bread containing 50 g of digestible carbohydrate.
  • By measuring blood glucose using a person consuming a test food and the glucose response curve obtained at various time points. This is repeated with the reference food. -- The index is the ratio of the area under the glucose response curves and is measured to the glucose.

Glycemic Index Value

• Area 2 (from glucose) has a value of 100, and the index for other foods is expressed relative to this.
• Glycemic index is the average result from 10 healthy individuals.

Glycemic Load

• Low glycemic index foods slow down the rate at which glucose is absorbed from the digestive tract.
• This is similar to soluble fibre.
• Factors that influence the glycemic index include fibre content, how the food is processed, the presence of fats/proteins and the physical/chemical properties of the food.
• Low glycemic index are helpful in diabetes/prevention management

Diabetes

• Disease characterized by the inability of body to produce / respond to insulin
• Three main types:
• Type 1: From an autoimmune disease that destroy the pancreas.
• Gestational: During pregnancy. Usually leads to high birth weight babies and may lead the babies prone to diabetes 2 later in life.
• Can be treated, reducing the risk to both mother and infant.
• Type 2: the most common - 90% of the cases.

Type 2 Diabetes

• Is characterized by insulin resistance of the muscle, liver, and adipose tissue and a reduced insulin secretion by the pancreas.
• In the insulin-resistant liver, gluconeogenesis, which is normally suppressed by insulin, continues, contributing to elevated blood glucose

Insulin Resistance

• Refers to a the state of muscles and adipose tissue DO NOT respond to stimulation by insulin to take up glucose.
• In the early stages of insulin resistance, the pancreas responds to the lack of response to insulin by increasing insulin secretion
  • The initial results is the lowering of blood glucose levels, but eventually the pancreas becomes exhausted and secretion of insulin is insufficient to maintain normal blood glucose levels.

Diabetes Blood Glucose Levels

• As insulin resistance develops and/or pancreatic function begins to decline, blood glucose rises to the pre-diabetes state.
• Treatment of pre-diabetes, with lifestyle changes, can often successfully normalize blood glucose levels.

Factors to Improve Type 2 Diabetes & Weight Management

• Obesity: major risk factors for the development
• Treatment:
  • Weight loss
    • Diet that is balanced
    • Exercise
• Medication if needed

Diabetes and Heart Disease

• Good Carbohydrates includes Foods high in soluble fibre
  • Helps lower blood cholesterol levels
  • Bile acids/ digest fats, from synthesed liver from cholesterol.
• BUT Soluble fibre tends to bind bile acids, causing less to return to the lover. Because less returns, liver has to use cholesterol.
• Bad Carbohydrates includes Foods high in free sugars may raise serum triglycerides a risk factor for cardiovascular disease.

Carbohydrates and Cancer

• Cancer the result of mutations in a cell's DNA that cause it to grow uncontrollably.
  • Single mutated cell - tumour and cells from that tumour can break free and spread to other parts called metastasis.
• Compounds that cause cancer carcinogens.
• Dietary carcinogens can
• Tumour initiators ( start mutations)
• Tumour promoters ( Promote the growth of established tumours).

Colon Cancer and Dietary Fibre

• reduce the risk of colon cancer
  • Fibre reduces contact time between intestinal cells and fecal contents, which may contain carcinogens
  • Fibre undergoes fermentation, producing short chain fatty acids
• high-fibre - antioxidants/phytochemicals

Non-Nutritive Sweeteners (Alternative Sweeteners)

• One alternative to sugars is non-nutritive sweeteners.
• These are sweeteners that, unlike sugars, contribute little or no kcalories to a food
• The safety of some of these compounds is controversial.
• Artificial: Stevia/Monk Fruit is Natural Sweetner - Articifical: Aspartame, Neotame, Advantame, Sucralose, Acesulfame K, Saccharin and Cyclamate, Sugar alcohols

Sugar Substitutes

• Safety concerns over weight gain
• dysfunction of the microflora,
• Human RCTs usually conclude that sugar substitutes do NOT have harmful effects
• Need for More research*

Aspartame/Sucralose

• Aspartame

  • Is a dipeptide / methylated phenylalanine.
  • Hydrolyzed to phenylalanine, aspartic acid phenylketonuria (PKU), avoid phenylalanine

• Sucralose (Splenda)

  • Molecule of sugar /prevent absorbed.
    • studies suggest May disrupt microflora

Canadian Guidlines (sugar substitutes)

• not be consumed(sugar) substitutes not essential.reduce intake ( sugar )
• "Eat everything in moderation."