Carbohydrates Sugars, Starch, Glycogen and Fibre

Carbohydrates Sugars, Starch, Glycogen and Fibre Part 1: Types of Carbohydrates Carbohydrates and Sugars. a) Carbohydrates - One of the macronutrients - The largest component of the diet and is a major source of energy for people throughout the world. - Includes staple food such as pasta, rice, beans, cassava and bread - About 50% of total calories consumed by North Americans come from carbohydrates. This is at the low end of the acceptable range. - According to the AMDR (acceptable macronutrient distribution range) recommendations, 45 to 65% of total calories should come from carbohydrates. - Carbohydrates are composed of carbon, hydrogen and oxygen molecules b) Carbohydrate Categories Two categories of carbohydrates 1. simple carbohydrates a. monosaccharide b. disaccharides 2. complex carbohydrates a. starch – provides energy b. glycogen – provides energy c. fibre – does not provides energy c) Carbohydrate Role in Nutrition - The primary role of carbohydrate is to supply energy so that protein is not used for energy and is conserved for protein synthesis. - Generally there are 4 kcal/g – except fibre (0 kcal/g) - Fibre is the only carbohydrate that provides no energy (calories per gram) in the diet - Alcohol sugars and alcohol both are made up of the carbon, hydrogen and oxygen molecules but they do not provide nutritional value so they are not considered as part of the carbohydrates main group. d) Simple Carbohydrates (Simple Sugar) - Simple carbohydrates are sugars, including both single sugar units and linked pairs of sugar units. - The basic sugar unit is a molecule containing six carbon atoms, together with oxygen and hydrogen atoms. - They are small molecules that require little to no digestion to be absorbed across the small intestine. Types of Simple carbohydrates 1. monosaccharide 2. disaccharides Monosaccharide - simple one molecule of sugar o Three types of monosaccharide 1. Glucose (blood sugar) - energy source that is running through your blood vessels at all times to feed various parts of your body (central nervous system and red blood cells). 2. Fructose ( fruit sugar) - Sweetest of the monosaccharides - Has a slightly different configuration; it still has the same number of carbons, a six carbon ring but it's a pentagon (5-sided) shape instead of the hexagon (6-sided). 3. Galactose Disaccharides - Two sugar molecules linked together to create a new sugar molecule. o Sucrose (table sugar) - glucose- fructose disaccharide o Maltose (malt sugar) - glucose - glucose disaccharide - produced during breakdown of starch o Lactose( milk sugar) - glucose - galactose disaccharide - The sugar in milk - Lactose intolerance — impaired ability to digest lactose due to insufficient quantity of the enzymes lactase (lactase cleaves the bond between the glucose and galactose in the lactose disaccharide). As a result, the lactose goes through the gut but is not broken down and thus not absorbed. As it travels to the large intestine bacteria feed on it producing lactose intolerance symptoms. Disaccharides are broken down during digestion and only glucose, fructose and galactose are absorbed into the bloodstream. e) Complex Carbohydrates (Polysaccharides) Polysaccharides - the word saccharide means sugar and poly means many. Complex carbohydrates are actually long chains of sugar units arranged together to form starches, glycogen or fibre (cellulose). - Starches are the plant storage form of carbohydrate o Humans have enzymes that can digest the bonds retrieving the glucose. - Glycogen is the human and animal storage form of carbohydrate o Humans have enzymes that can digest the bonds retrieving the glucose. - Cellulose (fibre) is the indigestible part of a plant food. o Humans don't have the enzyme that would be needed to digest fibre so it typically passes through the G.I. tract unchanged. There are some bacteria in our colon that can digest some cellulose (fibre) but most of it passes through unchanged. Complex Carbohydrate Sources Complex carbohydrates can be found in: - Whole grains (whole wheat bread) - Refined food - Bread, cereal, pasta, crackers, vegetables such as potatoes - Legumes such as black beans, kidney beans. f) Summary - Carbohydrates are composed of carbon, hydrogen, and oxygen atoms - The purpose of carbohydrates in the diet is to provide energy (4 kcal/g) and thus spare protein. - Other than milk, animal products do not contain carbohydrates. - Complex carbohydrates are long chains of glucose units - Starch is the term used for glucose storage in plants - Glycogen is the glucose storage in humans and animals - Fibre is part of the carbohydrate family but it does not provide calories. Part 2: The Body’s Need for Carbohydrates The Body's Need for Carbohydrate a) Carbohydrates for Energy - The body uses glucose for energy - Fructose and galactose are converted to glucose in the liver - The liver and muscles store glucose as the polymer glycogen - Glycogen is chains of linked glucose units Left: By NEUROtiker (Own work) [Public domain], via Wikimedia Commons Right: Image from Sizer, Whitney & Piche (2012) b) When the Body Needs Energy - When the body needs energy, glycogen, stored in the liver is cleaved to provide glucose that is delivered to the body tissues. - If glucose can't be derived from glycogen the body can form glucose from amino acids (gluconeogenesis) and to an insignificant level glycerol (the backbone of a triglyceride). - Glucose is the preferred energy source for brain cells, nerve cells, and developing red blood cells - Excess glucose in the blood stream will be used for energy or if not needed converted to fat and stored as adipose tissue. Starch Cellulose c) Carbohydrate Rich Foods: Source of Fibre - The body needs fibre found in carbohydrate rich foods - Human digestive enzymes cannot break the bond between the glucose molecules in fibre [cellulose] - Bacteria in the colon ferment some fibre for their energy needs - Most fibre provides no energy The starch molecules in the diagram have a V shaped link bond the body can break. Cellulose has a z like link bond humans do not have the enzymes to break. d) Types of Fibre Soluble or viscous fibre - Soluble in water - Form gels with water - Fermented by gut microflora Insoluble fibre - Not soluble in water - Non viscous - Not fermented - Structural part of plant e) Health Benefits of Fibre Intake a. Lowers blood cholesterol thus reduced ( ) risk of heart disease b. Modulates blood glucose levels thus reduced ( ) risk of diabetes c. Maintains healthy bowel function - Prevent constipation - Alleviate hemorrhoids - Prevent appendicitis - Prevent diverticulosis d. Fosters weight control f) Fibre and Blood Cholesterol Role of soluble or viscous fibre How can fibre lower blood cholesterol levels? - The liver makes cholesterol by using blood cholesterol - Cholesterol is stored in the gallbladder and then released into the intestine to help with fatty acid digestion If there is fibre in the diet, the fibre will bind some of the bile and be excreted into feces - Cholesterol can be reabsorbed if available but when it is bound by fibre it cannot be reabsorbed by the body. As such the body will need to use cholesterol from the liver to remake bile and replenish its’ stores. - In a low fibre diet, there is nothing to bind bile in the intestines. Very little cholesterolladen bile is excreted; most is recycled to the bloodstream creating a buildup. g) Fibre and Blood Glucose Control Soluble or viscous fibre - Traps glucose in its gel matrix - Delays transit of chyme in upper GI tract - Delays glucose absorption - Blunts post meal increase in blood glucose - Prevents spikes in insulin level h) Fibre and Bowel Health Insoluble fibre - Adds volume and softens the stool - Speeds up transit time through colon - Reduces pressure needed to evacuate rectum - Strengthens muscles of colon wall and prevents diverticula (sacs or outpouches of the intestinal wall due to a weakening in the muscle layers that encase the intestine. i) Fibre and Weight Control - High fibre foods are o Low fat o Low in added sugar o Less in energy dense - Insoluble fibres o Add bulk and feeling of fullness (satiety) o No calories - Soluble fibres o Slow transit through upper GI tract to enhance satiety o Contribute to feeling of fullness (satiety) with less calories j) Fibres Study Guide The chart in your textbook explains fibre, viscous vs non viscous, kind of food, and effects and health benefits. k) Summary 1. The main purpose of carbohydrate is to provide a source of energy and to spare protein. 2. Fibre plays an important role in health and is found in some carbohydrate rich foods. Part 3: Requirement and Excess Requirements for carbohydrate and the problems with excess a) Recommended carbohydrate intake - Total Carbohydrate DRI o Minimum: 130 g/day for adults and children (minimum acceptable, normal consumption for health is higher) o AMDR: 45–65% of total calories from carbohydrate o Most people should be consuming about 45 to 65% of their total calories coming from carbohydrates so in a 2000 kilocalorie diet that's about 300 g of carbohydrates. - Fibre DRI o AI: Men 19–50 yr 38 g/day o AI : Women 19–50 yr 25 g/day - Added Sugars (WHO) o Less than 10% of total kilocalories from sugar o A further reduction to below 5% or roughly 25 grams (6 teaspoons) per day would provide additional health benefits. b) Current Intake Reports Total Carabohydrate: - Canadians get about 50% of total calories from carbohydrates (low end of acceptable rate). Fibre intake: - Average intake - 14 to 15 g/day - Canadians consume less than recommended c) Added Sugar According to Statistics Canada, Canadians consume 26 tsp sugar per day (2004) - 21.4% of total energy intake Canadians are consuming carbohydrates within the acceptable macronutrient distribution ranges for carbohydrates however, they are consuming on average 21.4% of their total energy intake coming from sugar. The World Health Organization suggests 10%. In the diagram from Statistics Canada we can see that children from 9 to 18 are consuming much more than they should. Adults tend to taper their sugar habits. d) Sugar in Processed Foods - Most teenagers consume soft drinks daily - Soft drinks account for the largest component of adolescent sugar intake o 14% of sugar intake For every tablespoon of ketchup you put on your plate 1 teaspoon is straight sugar, sweetened yogurt contains 7 teaspoons of sugar. A 55 grams piece of chocolate has 8 tsp of sugar, that’s a lot of sugar Canadians are consuming. Food ½ c of canned corn 355 mL cola 1 tbs ketchup 230 g sweetened yogurt 55 g chocolate Sugar content 3 tsp 8 tsp 1 tsp 7 tsp 8 tsp