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Unit : II Macronutriets CARBOHYDRATES Presented by: Hezil Reema Barboza
Objectives learning At the end of class students will be able to • define the carbohydrates • list the sources of carbohydrates • Explain the RDA of carbohydrates • explain the function of carbohydrates • Describe about digestion , absorption and metabolism of carbohydrates
Carbohydrat es Proteins Minerals Fats Fiber Water Vitamins
What are carbohydrates? • Carbohydrates are the sugars, starches and fibers found in fruits, grains, vegetables and milk products. • Carbohydrates are macronutrients, meaning they are one of the three main ways the body obtains energy, or calories, "
Meaning : • Carbohydrates are biological molecules consisting of carbon, hydrogen, and oxygen atoms. • Like proteins and fats, they are macronutrients that are part of our daily diet.
A carbohydrate is an organic compound that is the body’s main source of energy. If you break down the word ‘carbohydrate’, you’ll find part of the names of its main components: carbon and hydrogen. A carbohydrate molecule also includes oxygen. Starch 1 hydrogen and 1 oxygen atom bonded to the rest of the molecule is called a hydroxyl group.
Simple carbohydrates consist of one or two sugars, found in very small molecules. Starches are complex carbohydrates, which are very large molecules made out of many simple carbohydrate units.
Using the sun’s energy and the green pigment in plants called chlorophyll, plants convert carbon dioxide and water into glucose and oxygen. Glucose is the basic sugar molecule from which all carbohydrates (sugars, starches, and fiber) are made.
Classification of carbohydrates Based on Chemical Classification/ number of single carbohydrate units found in each structure
Monosaccharides • Monosaccharides are simple sugars, which possess a free ketone or aldehyde group. • They are the building blocks of higher carbohydrates • Examples include glucose, fructose, galactose, glycerose, ribose, and ribulose.
Disaccharides: • Made up of two monosaccharide units bonded by glycosidic bond. • Sucrose= 1 molecule of glucose+ 1 molecule of fructose • Maltose: 2 molecules of glucose • Lactose: 1 molecule of glucose+ 1 molecule of galactose
Oligosaccharides • “Oligo” meaning few, oligosaccharides are sugars that break down into two to 10 molecules of monosaccharides when hydrolyzed. • Oligosaccharide examples include sucrose, maltose, lactose, raffinose, and stachyose.
Polysaccharides • “Poly” meaning many, polysaccharides are compound molecules that yield more than ten monosaccharide molecules on hydrolysis. • Polysaccharide examples include starch, cellulose, pectin, glycogen etc.
• Physiological Classification of Carbohydrates 1. Simple Carbohydrates • These include sugars like monosaccharides, disaccharides and oligosaccharides like trisaccharides and tetrasaccharides. • Simple carbohydrates are easily digested basic sugars that offer little health value for the body when taken in large amounts.
2. Complex Carbohydrates • The polysaccharides are complex carbohydrates that are considered good for health because it takes more time for the body to break them down. • They usually have a low glycemic load, meaning that you get lower amounts of sugar, which is released at a slower rate, producing small increases in blood sugar levels
3 building stocks of carbohydrates: sugars, starches and fiber • Sugars are simple carbohydrates like glucose, fructose and lactose. They cause a rapid rise in blood glucose levels.
• Starches are complex carbohydrates that are composed of several molecules of glucose. They cause a less rapid rise in blood glucose levels. • Fiber is a non-digestible complex carbohydrate. Our gut does not possess the enzymes needed to break apart the links between sugar units. Undigested fiber travels through our gut and while doing so, provides health benefits.
Calorie value of carbohydrate • It is the energy produced by one gram of carbohydrates. • The calorific value of one gram of carbohydrate is 4 KCal / g • (i. e. When one gram of carbohydrate is oxidized in the body, 4 KCal of energy is liberated )
Recommended daily allowance • Carbohydrates are the main source of energy for the body • 60 -70% of the total energy requirement of the body is provided by carbohydrates. • RDA- There is no fixed recommendation but minimum daily intake must be 100 - 150 grams • Only 10% of daily energy requirement must be provided by sugars and rest should come from complex carbohydrates
Dietary sources of carbohydrates Dietary carbohydrates are of two types: • Available( Digestible) carbohydrates • Unavailable( Indigestible) carbohydrates or dietary fibres.
Available( Digestible) carbohydrates • Part of carbohydrates that can be completely absorbed in the small intestine and can provide about 4 Calories per gram. • Available carbohydrates include: Starch, Sugars like glucose, fructose, galactose, mannose, Glycogen sucrose, lactose, maltose,
Dietary sources • starch : cereals, pulses, tubers etc. . • Glycogen: stored form of glucose in Animals • Sucrose: Table sugar, present fruits, sugar, beet etc. • Maltose: Malt, germinating seeds • Lactose: Milk and milk products • Glucose: Mainly present as starch. Free galucose can be seen in fruits like grapes, orange, watermelon etc. • Fructose: Present in some fruits and honey
Unavailable( Indigestible) carbohydrates or dietary fibers: • cannot be digested and absorbed in the small intestine. • Examples: Cellulose, hemicellulose, lignin, pectin, gum and mucilage etc. • Sources: Present in all vegetables, brans of cereals and hulls of legumes.
Functions of carbohydrates • • Chief source of energy Protein sparing action Prevent ketosis and muscle wasting Absolute requirement by brain Production of non essential amino acids Sweetening agents provides Taste Provides dietary fibers
Mouth • Carbohydrate digestion begins in the mouth. • The salivary glands in the mouth secrete saliva, which helps to moisten the food. • The food is then chewed while the salivary glands also release the enzyme salivary amylase, which begins the process of breaking down the polysaccharides in the carbohydrate food.
Stomach • After the carbohydrate food is chewed into smaller pieces and mixed with salivary amylase and other salivary juices, it is swallowed and passed through the esophagus. • The mixture enters the stomach where it is known as chyme. • There is no further digestion of chyme, as the stomach produces acid which destroys bacteria in the food and stops the action of the salivary amylase.
Pancreas and Small Intestine • In response to chyme being in the duodenum, the pancreas releases the enzyme pancreatic amylase, which breaks the polysaccharide down into a disaccharide, a chain of only two sugars linked together. • The small intestine then produces enzymes called lactase, sucrase and maltase, which break down the disaccharides into monosaccharides. • The monosaccharides are single sugars that are then absorbed in the small intestine.
Large Intestine (Colon) • Carbohydrates that were not digested and absorbed by the small intestine reach the colon where they are partly broken down by intestinal bacteria. • Fiber, which cannot be digested like other carbohydrates, is excreted with feces or partly digested by the intestinal bacteria.
Absorption of carbohydrates • The products of carbohydrate digestion are mainly glucose and in small amount fructose and galactose molecules. • They are absorbed from the intestinal lumen into the intestinal cells by different mechanisms. • Glucose, fructose and galactose are absorbed by facilitated diffusion • Glucose and galactose also absorbed by active transport • They are transported from the intestinal cells into the capillaries by facilitated diffusion
Metabolism of glucose Glycolysis: • Glucose is metabolized to pyruvate or lactate by glycolysis. • Glycolysis gives energy. Lactate is the end product of anaerobic glycolysis and pyruvate is the end product of aerobic glycolysis, which is then converted to Acetyl Co. A. Citric acid cycle: Acetyl Co. A enters Citric acid cycle for complete oxidation to Carbon Dioxide and water releasing energy.
Conclusion • Carbohydrates are one of the basic food groups — are important to a healthy life.
Evaluation • What is the function of carbohydrates ? • What are the sources? • What is the recommended daily allowance ?
References • Prasad RM. Text book of nutrition and biochemistry. 5 th ed: RM publications; 2014. • Swaminathan. Advanced Textbook on Food & Nutrition. Bappco. Bangalore: (2); 2015.