Carbohydrates provide main source of energy required to perform daily activities like walking, lifting, towing and cleaning. Carbohydrates are also called saccharides or sugars. Nowadays, people simply call them as “carbs”. Our body is made of millions of cells and each cell produces energy in the form of ATP (Adenosine triphosphate) mainly from carbohydrates by participating in various metabolic pathways. Our foods contain different types of carbohydrates. Based on structural complexity, carbohydrates are classified into simple sugars (e.g. glucose, fructose) or complex sugars (e.g.starch).
We need energy to perform our daily activities. If we do not get energy, we cannot work and we soon become sick and ill. It is just like charging batteries. Glucose (simple carbohydrate) is the main source of energy that our body requires. During digestion even complex carbohydrates like starch breakdown to glucose.
There are numerous sources of carbohydrates. However, selecting a carbohydrate diet is important because carbohydrates that contain simple sugars increase blood glucose levels faster than that of the complex sugars. If not utilized, they will be stored as fats and leads to obesity.Sweets, sugar, white bread, white flour, pastries, rice, honey are high in simple sugars and it is good to be away from them or use in very minimal quantities.
Fruits (not fruit juice because it contains lot of sugars like pineapple), vegetables, whole wheat, barley, oatmeal, brown rice, legumes, nuts, beans are good sources as many of them contain complex sugars. Complex sugars breakdown slowly and produce glucose slowly thereby maintaining blood glucose levels. Moreover these foods also provide fiber, vitamins and minerals.
Chemically, carbohydrates are polyhydroxy aldehydes or ketones. They contain carbon, hydrogen and oxygen atoms with a general formula of Cn(H2O)n. n increases from simple sugars to complex sugars.
Carbohydrates are classified into
a) Monosaccharides (simple sugars)
Contain a single chain or ring of polyhydroxy aldehydes or ketones. They cannot be broken down further. Based on the number of carbon atoms they are further divided into trioses, tetroses, pentoses and hexoses. Hexoses contain six carbon atoms e.g. glucose, mannose, galactose and fructose are hexoses.
b) Disaccharides
Two joined monosaccharides are called disaccharides. Monosaccharides are linked by glycosidic bonds. In our body, certain enzymes convert them into monosaccharides. These are hydrolysed by enzymes into two monosaccharides but not by bases e.g. sucrose, maltose, lactose
When digested
Sucrose gives one molecule of glucose and one molecule of fructose
Maltose gives two molecules of glucose
Lactose gives one molecule of galactose and one molecule of glucose
c) Oligosaccharides
Contain few monosaccharide chains linked to amino acids (e.g. glycoproteins) or lipids (e.g. glycolipids)
d) Polysaccharides
They are polymers made up of monosaccharides joined by glycosidic linkage. They are further divided into
Homopolysaccharides: When they hydrolyse they form same type of monosaccharides e.g. starch, glycogen, cellulose, chitin
Heteropolysaccharides: When they hydrolyse they form different types of monosaccharides e.g. heparin, hyaluronic acid, Pectie.
Starch is a polysaccharide made up of amylose and amylopectin. Potatoes, Corn (maize), wheat, potato, rice contains starch. During digestion, starch is hydrolysed by salivary or pancreatic amylase to maltose. This further hydrolyses to glucose by pancreatic enzymes in intestine and absorbed.
When we take simple sugars like glucose, it is immediately absorbed into the blood stream and gives immediate source of energy. However, when we take potatoes, corn (maize), wheat or rice they are first digested by enzyme called salivary amylase in mouth. Later, in intestine, in the presence of pancreatic amylases they are converted to oligosaccharides. Brush border enzymes in small intestine (dextrinase, gluco amylase) further break them to glucose, fructose or galactose. Glucose is absorbed into the blood and oxidized to produce immediate energy as ATP. Fructose and Galactose enters into liver and then converted to glucose.If our body does not require immediate energy, glucose is stored in liver as glycogen by insulin. If there is still excess glucose then it is converted to fats and makes obese. In order to reduce excess fat or when we fast we need to minimize the intake of carbohydrates. During fasting to give energy to our body, glycogen is converted to glucose in the presence of glucagon. When there is not sufficient glycogen available, fats start burning and produce energy. Fats and fatty acids cannot form glucose. During this process fats produce ketone bodies. Presence of ketone bodies in the blood is a dangerous situation. High levels of ketone bodies in blood cause metabolic acidosis and then coma. So the main source of our energy should come from carbohydrates. However, to avoid excess calories that make obese, try to get carbohydrates from good sources like vegetables, fruits and grains.
Researchers suggest that about 47% of our total daily calories should come from the carbohydrates especially from polysaccharides like starch. Only about 6 to 7 % should come from simple sugars. The carbohydrates requirement also depends on your daily calorie requirement.
Glycemic index (GI) is a scaled comparison of foods that contain carbohydrates to that of glucose that affect blood sugar levels. A low glycemic index means carbohydrates produce a slight fluctuation in blood glucose level whereas high GI means carbohydrates are estimated to produce high fluctuation range in blood glucose levels. So, intake of low GI carbohydrates could avoid risks of heart disease and diabetes.
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Low GI foods cause slow rise in blood glucose levels and contain GI less than 55 e.g. potato
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Intermediate GI foods contain GI between 55 and 70 e.g. fruits like pineapple
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High GI foods cause rapid blood glucose levels and contain GI more than 70 e.g. sweets
When we take excess carbohydrates, excess glucose is formed and it elevates blood glucose levels. If our body does not require immediate energy, glucose is stored in liver and muscle as glycogen by insulin. If there is still excess glucose, then it is converted to fats and makes obese. Being obese increases the risk of heart problems and diabetes.
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