Carbohydrates

Carbohydrates and energy

Why is  it important to consume carbohydrates?  Carbohydrates is a readily available energy source of our body compared to other nutrients protein and fat which needs more time to process.   They generates  4 kilocalories per gram of food.  Whether you eat grains or fruits, they all same in terms of calorie making.  AMDR for  carbohydrate is 45%-65%, fat is 20%-35% and of protein is 10%-35% of your total kilocalorie (Kcal) intake.  ADMR describes the portion of the energy intake that should come from each macronutriet.  It stands for Acceptable Macronutrient Distribution Ranges and can also be understood as the calorie composition of a diet that gives adequate energy as required and other nutrients.

Carbohydrates and monosaccharides

What are carbohydrates?  They are made up of varying numbers of sugar molecule.  The simplest types of carbohydrate are called sugars. Carbohydrates consist of one sugar molecule is called monosaccharides.  For example, glucose (the most abundant sugar in blood), fructose (the mosta bundant sugar in fruits and vegetables), and galactose (found in dairly products) are belong to monosaccharide.  Glucose and galactose are used as a source of energy (ATP).  Glucose is the only energy source for red blood cell.  Therefore, it is very important to consume enough vegetables and fruits. 

Disaccharides

Second, disaccharides consist of two monosaccharies bonded together.  The most common disaccarides are lactose (galactose and glucose), maltose (glucose and glucose), and sucrose (fructose and glucose). The lactose is the most abundant in milk.  While many babies produce enough enzyme, lactase, to digest the high amount of lactose found in milk, some people doesn't not have enough lactase so they can't breakdown lactose into galactose and glucose.  This is called lactose intolerance.  Maltose is not found in many food; however, it is formed by breakdown of starches.  For example, during the brewing process, cereal starch such as barley are converted to maltose.  Sucrose is found in many plants, such as sugar cane and sugar beets. 

Polysaccharides

Finally, one of the most nutritious carbohydrates, complex carbohydrates consist of many monosaccharides. Also, the complex carbohydrates are divided into oligosaccharides and polysaccharides.  The oligosaccharides are components of cell membrane.  They include dried beans, soybeans, peas, and lentils.  They are raffinose and stachyose.  Because humans lack the enzymes needed to digest these two carbohydrates, they pass undigested into large intestine, where bacteria break them down.  As a result, some people experience abdominal discomfort (bloating and cramps) and flatulence (gas).  Oligosaccharides are also made in the breasts as a human milk.  This helps infants from disease-causing pathogens; therefore, breastfeeding is encouraged to women.

Amylose and amylopectin

Polysaccharides are made up of many monosaccharides bonded together by glycosidic bonds.  Through photosynthesis, plants synthesize glycosidic bonds.  Some polysaccharides have an orderly linear appearance, whereas others are shaped like branches on a tree.  The three most common polysaccharides are starch, fiber, and glycogen. 

To store this importance source of energy plants convert the glucose for starch.    There are two types of starch, amylose (linear structure with alpha-1,4 glycosidic bond) and amylopectin (branched structure with alpha-1,6 glycosidic bond).  Amylopectin is more easy to digested because of branched points can make enzymes can hydrolyze multiple glycosidic bonds simultaneously.  As a result our bodies can breakdown glycogen quickly when we need energy.  

Because of its tightly packed structure, amylose is more resistant to digestion than other starch molecules. Therefore, amylose has been found to be an effected prebiotic.  Unlike amylopectin, amylose is insoluble in water.  Plants generally contain a mixture of both types of starch – amylose and amylopectin.  Examples of starch foods are grains (such as corn, rice, and wheat), products made from grains (pasta and bread), and legumes (beans, lentils, and split peas).  Potatoes, sweet potatoes, and winter squashes also source of starch. 

Amylopectin is a soluble polysaccharide and highly branched polymer of glucose found in plants. Branching takes place with α(1→6) bonds occurring every 24 to 30 glucose units, resulting in a soluble molecule that can be quickly degraded as it has many end points for enzymes to attach onto. In contrast, amylose contains very few α(1→6) bonds, or even none at all.  This causes it to be hydrolyzed more slowly but have higher density and be insoluble.  Its counterpart in animals is glycogen, which has the same composition and structure, but with more extensive branching that occurs every 8 to 12 glucose units.  Humans and other animals that eat plant foods also use amylase, an enzyme that assists in breaking down amylopectin.  Starch is made of about 70% amylopectin by weight, though it varies depending on the source (higher in medium-grain rice to 100% in glutinous rice, waxy potato starch, and waxy corn, and lower in long-grain rice, amylomaize, and russet potato).  Amylopectin is highly branched, being formed of 2,000 to 200,000 glucose units. Its inner-chains are formed of 20-24 glucose subunits.

Dissolved amylopectin starch  has a lower tendency of retrogradation r(gelling) during storage and cooling. For this main reason the waxy starches are used in different applications mainly as thickening agent or stabilizer.  

Fiber

Unlike starch, fiber cannot be digested in the human small intestine.  This is due to its structure, beta-glycosidic bond that are resistant to digestive enzymes.  Undigested fiber passes from the small to the large intestine relatively intact. Then, intestinal bacteria began to break down the fiber, producing gas, lipids, and other substances.  Moreover, dietary fiber promotes the selective growth of beneficial intestinal bacteria, which is turn help inhibit the growth of other disease-causing (pathogenic) bacteria.  

Also, fiber is categorized according to its solubility in water.  Soluble and viscous dietary fiber, for example, is found in oats, barley, legumes, rice bran, psylium seeds, soy, and some fruits.  These foods help soften fecal matter, reduction strain and making elimination easier.  Moreover, they help reduce cholesterol levels in some people.  According to research, the viscous fiber may bind with dietary fat and cholesterol in the gastrointestinal (GI) track making it less likely to be absorbed.  

Insoluble dietary fiber is cellulose and hemicellulose.  Cellulose is the most abundant insoluble dietary fiber in food.  Whole-grain four, wheat bran, whole-grain  breakfast cereals, seeds, and many vegetables including carrots, broccoli, celery, peppers and cabbage.  Because insoluble fiber do not dissolved in water, they do not form viscous gels.  Nor do bacteria in the GI tract, which helps to increase fecal weight and volume.  Generally, large amounts of fecal mass move through the colon quickly by stimulating peristalsis contractions in the colon, propelling the material forward.  When consumed with sufficient amounts of fluid, insoluble fiber can help prevent and alleviate constipation.

Dietary Reference Intakes for Carbohydrates

The Institute of Medicine's Dietary Reference Intakes (DRIs) are based maily on ensuring that the brain has adequate glucose for its energy needs.  The  USDA (United States Department of Agriculture) recommends people to take 130g per day for adults, minimum amount of glucose utilized by the brain.  As there are 4 kcal per gram of carbohydrate, this means a person needing 2,000 kcal daily should consume between 225 and 325 g of carbohydrates (900 and 1,300 kcal, respectively).    

Sources  

McGuire, M. & Beerman, K. A. (2011),  Nutritional Sciences.  New York; Wadsworth

Food and Drug Administration (2013). Claims That Can Be Made for Conventional Foods and Dietary   Supplements. Retrieved on 09/12/2013 from.  http://www.fda.gov/Food/IngredientsPackagingLabeling/LabelingNutrition/ucm111447.htm