Fundamentals of Human Nutrition/Defining Carbohydrates
4.1 Defining Carbohydrates
4.1.1 Introduction to Carbohydrates
- Carbohydrates are often given a bad report, even by doctors who certainly should know better. This misconception only serves to further confuse an already muddled public.
- The confusion comes about when we try to lump all carbohydrates into one category and fail to differentiate between the different types.
- On the other hand, when a differentiation is made, it is often only between two types of carbohydrates: simple and complex. This even further muddles the discussion. In this section we will be discussing three types of carbohydrates:
- Processed simple
- First, we will start with the source of all carbohydrates. All carbohydrates originate from plants. Carbohydrates have one purpose, and that is to create glucose in the blood,hence the reason for proteins and fats not being listed on the glycemic index. The glucose is then transported through the blood to the mitochondria of each cell where it is used to produce the energy molecule, adenosine triphosphate. Without this high energy molecule, there would be no energy for life's processes. Proteins and fats, the other two macronutrients covered later in this text do not do this. They are digested in a different manner.
Carbohydrates are one of the three macronutrients that make up the typical human diet. They make up about half of an average daily caloric intake. Carbohydrates include sugars, starches, and cellulose. They are formed via photosynthesis in green plants. This is accomplished in plants via a pigment known as chlorophyll that absorbs light energy. As seen in Figure 4A, plants convert carbon dioxide (CO2), water (H2O), and energy (sunlight) into oxygen (O2) and glucose, a simple carbohydrate. The chemical equation for this reaction is 6CO2 + 6H2O + light energy → 6O2 + C6H12O6
Figure 4A: Photosynthesis
Some of this glucose is used as energy, some goes on to make cellulose as structural support for the plant, and the rest is converted to alternative chemical forms. Usually, this alternative form is starch, which is stored for later use. The carbohydrates produced by plants are essential for the energy of animals. Animals eat plants and utilize the energy in the carbohydrates through the process of respiration. Respiration takes the carbohydrates from plants and oxygen and converts it to energy, CO2, and water. The energy produced is then used for cell work throughout the body.
Each carbohydrate has the same generic makeup; CnH2nOn, which could also be written as Cn(H2O)n. The formula for glucose is found by using n=6 in this formula. Thus, glucose is C6H12O6. Figure 4B shows the structure of glucose. Fructose is a very similar sugar to glucose and they have the same formula, C6H12O6. However, fructose has a very different structure, seen here. The cyclic form of glucose, pictured here, is a 6-membered ring with an intramolecular hemiacetal formed by a straight-chain aldehyde. Fructose, on the other hand, forms a 5-membered cyclic hemiketal from a straight-chain ketone. These different structural formations cause glucose and fructose to have different functions, as well.
Figure 4B: Glucose and Fructose
Glucose is found in some fruits, vegetables, and honey. In the human body, it is known as blood sugar. Fructose is found in fruits, honey, and corn syrup. It is also known as fruit sugar. Glucose and Fructose are simple carbohydrates (monosaccharaides). More complex carbohydrates (polysaccharides) are made up of multiple monosaccharaides bonded together. Both complex and simple carbohydrates can be part of a healthy diet.
Glucose is found in some fruits, vegetables, and honey. In the human body, it is known as blood sugar. Fructose is found in fruits, honey, and corn syrup. It is also known as fruit sugar. Glucose, Fructose, and Galactose are simple carbohydrates (monosaccharaides). Sucrose, Maltose, and Lactose are combinations of two monosaccharides (disaccharides) which are also considered to be simple carbohydrates. More complex carbohydrates (polysaccharides) are made up of multiple monosaccharaides bonded together. Both complex and simple carbohydrates can be part of a healthy diet. This group of foods may include vegetables like kale, spinach, broccoli, collard greens, and mustard greens. These are said to be the dark green vegetables. Within these plants you find every vitamin, water soluble or fat soluble known to man. Phyto-meaning plant-chemicals are those compounds science has recently discovered that have protective properties against degenerative diseases such as cancer. These compounds are found only within this treasure chest of preventative medicines of nature. Grains like brown rice are an example of another plant grown for human consumption that falls into the complex carbohydrate category. The reason vegetables still look like vegetables by the time they get to the consumers' table and brown rice remains brown is because they are not subjected to the extreme milling process that produces flour. There are three layers to the rice kernel, husk or hull,(for protection and has no nutrients) bran layer, endosperm, and the embryo. During milling only the husk is removed. The brown bran layer, containing all the vitamins and minerals is left intact.
Monosaccharides Definition : Sweet, colorless, crystalline structure which contain one (mono) molecule of sugar (saccharide), with the basic CnH2nOn makeup. One of the smallest units in the class of carbohydrates and they cannot be decomposed by hydrolysis. Monosaccharides can combine with one other monosaccharides to form disaccharides or with many other monosaccharides to form polysaccharides. There are three of these sugars and they are Fructose,Glucose, and Galactose  followed here in detail: references 1. ↑http://ghr.nlm.nih.gov/glossary=monosaccharides 2. ↑http://hyperphysics.phy-astr.gsu.edu/hbase/organic/sugar.html 3. ↑http://www.elmhurst.edu/~chm/vchembook/543fructose.html
Glucose Also known as blood sugar and Dextrose. It is made in plants by photosynthesis, whereby the light energy works with chlorophyll in chloroplasts to convert CO2 to Glucose. It is structurally, C6H12O6. This the same for all monosaccharides. The difference between the three comes from the arrangement of their atoms. This is what accounts for the varying sweetness among monosaccharides. This sugar is an aldehyde, however. It requires no digestion to be absorbed by humans, thus its use for intravenous feeding. Glucose is essential in the body for energy and for many physiological processes to be carried out. Glucose is one of the two sugars is every disaccharide, when glucose combines with itself, the disaccharide formed is called maltose. References 1. ↑http://ghr.nlm.nih.gov/glossary=monosaccharides 2. ↑http://hyperphysics.phy-astr.gsu.edu/hbase/organic/sugar.html 3. ↑http://www.elmhurst.edu/~chm/vchembook/543fructose.html
Fructose Also known as fruit sugar, or called earlier, aslevulose. It is an isomer of Glucose found in plants and honey. Honey was turned into Fructose by the bee's enzyme converting by hydrolysis, the compound, Sucrose (the combination of these two simple sugars discussed, and below under Polysaccharides as a Disaccharide.) As mentioned above, it also has C6H12O6 for its structure, but the linear construction is different because it is a ketone. Fructose is considered to be the sweetest tasting sugar. When fructose combines with glucose, the disaccharide sucrose is formed which is also very sweet due to the fructose in its composition. References 1. ↑http://hyperphysics.phy-astr.gsu.edu/hbase/organic/sugar.html 2. ↑http://hyperphysics.phy-astr.gsu.edu/hbase/organic/sugar.html 3. ↑http://www.elmhurst.edu/~chm/vchembook/543fructose.html
Galactose Also known as milk sugar. It is not found very often free in food, as it is usually ingested as lactose (the disaccharide that galactose is apart of), but it is found in peas. It shares the same chemical composition of glucose and fructose but the arrangement of its atoms are different. Galactose is much less sweet that glucose and fructose. Galactose, when combined with glucose, forms the disaccharide lactose. References 1. http://themedicalbiochemistrypage.org/galactose.php 2. http://chemistry.elmhurst.edu/vchembook/543galactose.html 3. http://www.ncbi.nlm.nih.gov/pubmed/8246770
4.1.3 Complex carbohydrates
Complex carbohydrates form one of the main dietary components. Carbohydrates are one of the three essential macronutrients required for the full functioning of the human body. They include sugars, starches, and fibers. Simple carbohydrates are sugars while complex carbohydrates include starch and fiber. They provide energy for the body, especially the brain and the nervous system. The energy is also used for functions like heartbeat, digestion, breathing and body movement. An enzyme, amylase, breaks down the carbs into glucose that is used for energy. Starch in food must be broken down through digestion before the body can use it as a dietary source.
Complex carbohydrates consist of sugar molecules stuck together in long chains and branches. The body turns both simple and complex carbohydrates into glucose (blood sugar). Glucose is used in the cells of the body and in the brain. Any unused glucose is stored in the liver and muscles as glycogen for use later. Due to their complexity, complex carbohydrates take a little longer to digest, and they don't raise the sugar levels in the blood as quickly as simple carbohydrates. They act as the body's fuel, and they contribute significantly to energy production.
They are found in a variety of foods, including grains, vegetables and legumes - Examples of foods that contain complex carbohydrates include spinach, yams, broccoli, beans, zucchini, lentils, skimmed milk, whole grains, like, millet, oats, wheat germ, barley, wild rice, brown rice, buckwheat, oat bran, cornmeal, amaranth and many other leguminous plants and vegetables. Complex carbohydrates, such as whole grains, contain more nutrients and fiber than simple carbohydrates, such as sugar. Products made from these grains are complex too, like, grain bread, pasta, bagels, buns and rolls, macaroni, breakfast cereals. Complex carbohydrates are also low-glycemic, meaning they have a mild impact on your blood sugar and can enhance appetite control, weight management and energy.
Complex carbohydrate foods provide vitamins, minerals, and fiber that are important to the health of an individual. The majority of carbohydrates should come from complex carbohydrates (starches) and naturally occurring sugars, rather than processed or refined sugars, which do not have the vitamins, minerals, and fiber found in complex and natural carbohydrates. Refined sugars are often called "empty calories" because they have little to no nutritional value. The daily recommendation for dietary fiber – 14 grams for every 1000 calories – is not met by most. Examples of foods made with refined flour include breads, rolls, buns and pizza crust, which are unfavorable sources of fiber. Instead, increasing consumption of beans, peas, vegetables, fruits, whole grains, nuts, seeds and foods with natural fiber would be preferable and more beneficial. Some dairy products such as low-fat milk, low-fat yogurt, or skim milk are also good choices for complex carbohydrates in diet.
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Fiber Complex carbohydrates include disaccharides and polysaccharides. The main disaccharides include three pairs of monosaccharides: maltose, sucrose, and lactose. All three of these disaccharides include a glucose bonded to either another glucose, a fructose, or a galactose, respectively. Sucrose is table sugar and lactose can be found in dairy products. Polysaccharides are much more complicated and can involve multiple units of glucose or even multiple strings of monosaccharides . Most all dietary fibers are polysaccharides.
Disaccharides are two monosaccharides bonded together by a covalent bond . In “Effect of Diet upon Intestinal Disaccharidases and Disaccharide Absorption,” a group of laboratory rats were made to fast for 3 days and then fed either a high sucrose diet – a disaccharide rich diet – or casein, used as a control group. The first group was observed to have extremely heightened sucrase and maltase activity . This leads us to believe that a high dose of disaccharides can affect one's gastrointestinal tract as well as absorption of other disaccharides and polysaccharides.
Polysaccharides fall into two main groups: starches made exclusively from plant matter, and glycogen made from animals. Cellulose is another common polysaccharide, made from cell walls of plants, consisting of long chains of glucose. However, animals cannot digest this type of polysaccharide as it contains beta bonds that require a certain enzyme present to be digested. Humans do not have this enzyme in their digestive system, which is why cellulose is not considered a nutrient. In humans, the main purpose of glycogen and starch is to act as readily available storage of glucose. When more glucose is consumed than needed at the moment, the liver will store the excess as glycogen. When glucose levels are low, the liver will convert the stored glycogen back into glucose ready for use . Starches are a polysaccharide that contain 300 to 1000 units of glucose bonded together. Starches come from plants, and is formed within a grain. These grains contain a hard outer layer. Humans can digest starches as they are smaller molecules that cellulose and more bioavailable to be used for energy . A study in the IEEE scientific journal on certain types of fungi in China and the polysaccharides extracted from them revealed that the polysaccharides contain anti-aging properties as well as anti-infection and anti-tumor properties .
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