What are carbohydrates?
What are complex carbohydrates?
What are simple carbohydrates?
Why are carbohydrates important?
What Is the Difference Between Sucrose, Glucose & Fructose?
Glycolysis
Carbohydrates - What are carbohydrates?
What are carbohydrates?
All carbohydrates are made up from sugars. There are a number of different types of sugars but in the body all carbohydrates metabolism converts sugar to glucose, our body's preferred energy source. Glucose is the main sugar present in many foods but some contain different sugars, such as fructose in fruit, lactose in milk, galactose as well as others. Most sugars are digested and absorbed and converted to glucose, some cannot be digested, we call this fiber.
What are complex carbohydrates?
Complex carbohydrates or starch are simply sugars bonded together to form a chain. Digestive enzymes have to work much harder to access the bonds to break the chain into individual sugars for absorption through the intestines.
For this reason digestion of complex carbohydrates takes longer. The slow absorption of sugars provides us with a steady supply of energy and limits the amount of sugar converted into fat and stored!
What are simple carbohydrates?
Simple carbohydrates are smaller molecules of sugar unlike the long chains in starch. For example the individual sugars themselves - glucose, fructose and galactose ( monosaccharides ), or two sugars bonded together ( disaccharides ).
They are digested quickly because the individual sugars are ready to be absorbed immediately plus digestive enzymes have easy access to the bonds in the paired molecules. You could say most of the work has been done!
Absorption of simple carbohydrates
Their rapid absorption increases the chances of sugar converting to fat but only if there is an abundance of energy absorbed. Foods like cake, pastry, biscuits, chocolate and too much table sugar to name a few contain lots of "empty" calories. Because our cells usually do not require that amount of energy at that time, the sugar must either be converted to glycogen ( sugar storage within cells ) or converted to fat. The cell can only store a limited amount of glycogen so in many cases simple carbohydrates loaded foods may contribute to body fat stores. This rule can change if the glycogen levels are low such as after anaerobic exercise.
Other natural foods like fruit contain naturally occurring simple sugars, however because the amount of energy is low there's less chance for sugar to be converted to fat. Plus many fruits are high in fiber which helps slow digestion again limiting the flood of sugar energy into cells when its not needed!
Why are carbohydrates important?
Carbohydrates are the body's primary source of fuel. The energy can be released quickly and easily to fulfill immediate requirement within cells. Carbohydrates do not require oxygen to burn therefore they fuel most muscular contractions, meaning our carbohydrate intake is very important for regular exercise sessions. If carbohydrates stores are low exercise will seem like a real effort!
Carbohydrate Metabolism
Carbohydrates made up of carbon, hydrogen, and oxygen atoms are classified as mono-, di-, and polysaccharides, depending on the number of sugar units they contain. The monosaccharides— glucose , galactose, and fructose—obtained from the digestion of food are transported from the intestinal mucosa via the portal vein to the liver. They may be utilized directly for energy by all tissues; temporarily stored as glycogen in the liver or in muscle; or converted to fat , amino acids , and other biological compounds.
Carbohydrate metabolism plays an important role in both types of diabetes mellitus. The entry of glucose into most tissues—including heart, muscle, and adipose tissue —is dependent upon the presence of the hormone insulin . Insulin controls the uptake and metabolism of glucose in these cells and plays a major role in regulating the blood glucose concentration. The reactions of carbohydrate metabolism cannot take place without the presence of the B vitamins , which function as coenzymes. Phosphorous, magnesium, iron , copper, manganese, zinc and chromium are also necessary as cofactors.
Carbohydrate metabolism begins with glycolysis , which releases energy from glucose or glycogen to form two molecules of pyruvate, which enter the Krebs cycle (or citric acid cycle), an oxygen-requiring process, through which they are completely oxidized. Before the Krebs cycle can begin, pyruvate loses a carbon dioxide group to form acetyl coenzyme A (acetyl-CoA). This reaction is irreversible and has important metabolic consequences. The conversion of pyruvate to acetyl-CoA requires the B vitamins.
The hydrogen in carbohydrate is carried to the electron transport chain, where the energy is conserved in ATP molecules. Metabolism of one molecule of glucose yields thirty-one molecules of ATP. The energy released from ATP through hydrolysis (a chemical reaction with water) can then be used for biological work.
Only a few cells, such as liver and kidney cells, can produce their own glucose from amino acids, and only liver and muscle cells store glucose in the form of glycogen. Other body cells must obtain glucose from the bloodstream.
Under anaerobic conditions, lactate is formed from pyruvate. This reaction is important in the muscle when energy demands exceed oxygen supply. Glycolysis occurs in the cytosol (fluid portion) of a cell and has a dual role. It degrades monosaccharides to generate energy, and it provides glycerol for triglyceride synthesis. The Krebs cycle and the electron transport chain occur in the mitochondria . Most of the energy derived from carbohydrate, protein, and fat is produced via the Krebs cycle and the electron transport system.
Glycogenesis is the conversion of excess glucose to glycogen. Glycogenolysis is the conversion of glycogen to glucose (which could occur several hours after a meal or overnight) in the liver or, in the absence of glucose-6-phosphate in the muscle, to lactate. Gluconeogenesis is the formation of glucose from noncarbohydrate sources, such as certain amino acids and the glycerol fraction of fats when carbohydrate intake is limited. Liver is the main site for gluconeogenesis, except during starvation, when the kidney becomes important in the process. Disorders of carbohydrate metabolism include diabetes mellitus, lactose intolerance , and galactosemia .
What Is the Difference Between Sucrose, Glucose & Fructose?
Sucrose, glucose and fructose are important carbohydrates, commonly referred to as simple sugars. Sugar is found naturally in whole foods and is often added to processed foods to sweeten them and increase flavor. Your tongue can't quite distinguish between these sugars, but your body can tell the difference. They all provide the same amount of energy per gram, but are processed and used differently throughout the body.
Structure
Simple carbohydrates are classified as either monosaccharides or disaccharides. Monosaccharides are the simplest, most basic units of carbohydrates and are made up of only one sugar unit. Glucose and fructose are monosaccharides and are the building blocks of sucrose, a disaccharide. Thus, disaccharides are just a pair of linked sugar molecules. They are formed when two monosaccharides are joined together and a water of molecule is removed -- a dehydration reaction.
Glucose
The most important monosaccharide is glucose, the body’s preferred energy source. Glucose is also called blood sugar, as it circulates in the blood, and relies on the enzymes glucokinase or hexokinase to initiate metabolism. Your body processes most carbohydrates you eat into glucose, either to be used immediately for energy or to be stored in muscle cells or the liver as glycogen for later use. Unlike fructose, insulin is secreted primarily in response to elevated blood concentrations of glucose, and insulin facilitates the entry of glucose into cells.
Fructose
Fructose is a sugar found naturally in many fruits and vegetables, and added to various beverages such as soda and fruit-flavored drinks. However, it is very different from other sugars because it has a different metabolic pathway and is not the preferred energy source for muscles or the brain. Fructose is only metabolized in the liver and relies on fructokinase to initiate metabolism. It is also more lipogenic, or fat-producing, than glucose. Unlike glucose, too, it does not cause insulin to be released or stimulate production of leptin, a key hormone for regulating energy intake and expenditure. These factors raise concerns about chronically high intakes of dietary fructose, because it appears to behave more like fat in the body than like other carbohydrates.
Sucrose
Sucrose is commonly known as table sugar, and is obtained from sugar cane or sugar beets. Fruits and vegetables also naturally contain sucrose. When sucrose is consumed, the enzyme beta-fructosidase separates sucrose into its individual sugar units of glucose and fructose. Both sugars are then taken up by their specific transport mechanisms. The body responds to the glucose content of the meal in its usual manner; however, fructose uptake occurs at the same time. The body will use glucose as its main energy source and the excess energy from fructose, if not needed, will be poured into fat synthesis, which is stimulated by the insulin released in response to glucose.
Protein Metabolism
Proteins contain carbon, hydrogen, oxygen, nitrogen , and sometimes other atoms. They form the cellular structural elements, are biochemical catalysts, and are important regulators of gene expression . Nitrogen is essential to the formation of twenty different amino acids, the building blocks of all body cells. Amino acids are characterized by the presence of a terminal carboxyl group and an amino group in the alpha position, and they are connected by peptide bonds.
Digestion breaks protein down to amino acids. If amino acids are in excess of the body's biological requirements, they are metabolized to glycogen or fat and subsequently used for energy metabolism. If amino acids are to be used for energy their carbon skeletons are converted to acetyl CoA, which enters the Krebs cycle for oxidation, producing ATP. The final products of protein catabolism include carbon dioxide, water, ATP, urea, and ammonia.
Vitamin B 6 is involved in the metabolism (especially catabolism) of amino acids, as a cofactor in transamination reactions that transfer the nitrogen from one keto acid (an acid containing a keto group [-CO-] in addition to the acid group) to another. This is the last step in the synthesis of nonessential amino acids and the first step in amino acid catabolism. Transamination converts amino acids to L-glutamate, which undergoes oxidative deamination to form ammonia, used for the synthesis of urea. Urea is transferred through the blood to the kidneys and excreted in the urine.
The glucose-alanine cycle is the main pathway by which amino groups from muscle amino acids are transported to the liver for conversion to glucose. The liver is the main site of catabolism for all essential amino acids, except the branched-chain amino acids, which are catabolized mainly by muscle and the kidneys. Plasma amino-acid levels are affected by dietary carbohydrate through the action of insulin, which lowers plasma amino-acid levels (particularly the branched-chain amino acids) by promoting their entry into the muscle.
Body proteins are broken down when dietary supply of energy is inadequate during illness or prolonged starvation. The proteins in the liver are utilized in preference to those of other tissues such as the brain. The gluconeogenesis pathway is present only in liver cells and in certain kidney cells.
Disorders of amino acid metabolism include phenylketonuria , albinism, alkaptonuria, type 1 tyrosinaemia, nonketotic hyperglycinaemia, histidinaemia, homocystinuria, and maple syrup urine disease.
Fat (Lipid) Metabolism
Fats contain mostly carbon and hydrogen, some oxygen, and sometimes other atoms. The three main forms of fat found in food are glycerides (principally triacylglycerol [triglyceride], the form in which fat is stored for fuel), the phospholipids , and the sterols (principally cholesterol ). Fats provide 9 kilocalories per gram (kcal/g), compared with 4 kcal/g for carbohydrate and protein. Triacylglycerol, whether in the form of chylomicrons (microscopic lipid particles) or other lipoproteins , is not taken up directly by any tissue, but must be hydrolyzed outside the cell to fatty acids and glycerol, which can then enter the cell.
Fatty acids come from the diet , adipocytes (fat cells), carbohydrate, and some amino acids. After digestion, most of the fats are carried in the blood as chylomicrons. The main pathways of lipid metabolism are lipolysis, betaoxidation, ketosis , and lipogenesis.
Lipolysis (fat breakdown) and beta-oxidation occurs in the mitochondria. It is a cyclical process in which two carbons are removed from the fatty acid per cycle in the form of acetyl CoA, which proceeds through the Krebs cycle to produce ATP, CO 2 , and water.
Ketosis occurs when the rate of formation of ketones by the liver is greater than the ability of tissues to oxidize them. It occurs during prolonged starvation and when large amounts of fat are eaten in the absence of carbohydrate.
Metabolism
Lipogenesis occurs in the cytosol. The main sites of triglyceride synthesis are the liver, adipose tissue, and intestinal mucosa. The fatty acids are derived from the hydrolysis of fats, as well as from the synthesis of acetyl CoA through the oxidation of fats, glucose, and some amino acids. Lipogenesis from acetyl CoA also occurs in steps of two carbon atoms. NADPH produced by the pentose-phosphate shunt is required for this process. Phospholipids form the interior and exterior cell membranes and are essential for cell regulatory signals.
Cholesterol Metabolism
Cholesterol is either obtained from the diet or synthesized in a variety of tissues, including the liver, adrenal cortex, skin, intestine, testes, and aorta. High dietary cholesterol suppresses synthesis in the liver but not in other tissues.
Carbohydrate is converted to triglyceride utilizing glycerol phosphate and acetyl CoA obtained from glycolysis. Ketogenic amino acids, which are metabolized to acetyl CoA, may be used for synthesis of triglycerides. The fatty acids cannot fully prevent protein breakdown, because only the glycerol portion of the triglycerides can contribute to gluconeogenesis. Glycerol is only 5 percent of the triglyceride carbon.
Most of the major tissues (e.g., muscle, liver, kidney) are able to convert glucose, fatty acids, and amino acids to acetyl-CoA. However, brain and nervous tissue—in the fed state and in the early stages of starvation—depend almost exclusively on glucose. Not all tissues obtain the major part of their ATP requirements from the Krebs cycle. Red blood cells, tissues of the eye, and the kidney medulla gain most of their energy from the anaerobic conversion of glucose to lactate.
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Carbohydrates
are one of three macronutrients that provide the body with
energy
(
protein
and fats being the other two). The chemical compounds in carbohydrates
are found in both simple and complex forms, and in order for the body to
use carbohydrates for energy, food must undergo digestion,
absorption
, and
glycolysis
. It is recommended that 55 to 60 percent of caloric intake come from
carbohydrates.
Chemical Structure
Carbohydrates are a main source of energy for the body and are made of
carbon, hydrogen, and
oxygen
. Chlorophyll in plants absorbs light energy from the sun. This energy is
used in the process of photosynthesis, which allows green plants to take
in carbon dioxide and release oxygen and allows for the production of
carbohydrates. This process converts the sun's light energy into a
form of chemical energy useful to humans. Plants transform carbon dioxide
(CO
2
) from the air, water (H
2
O) from the ground, and energy from the sun into oxygen (O
2
) and carbohydrates (C
6
H
12
O
6
) (6 CO
2
+ 6 H
2
O + energy = C
6
H
12
O
6
+ 6 O
2
). Most carbohydrates have a ratio of 1:2:1 of carbon, hydrogen, and
oxygen, respectively.
Humans and other animals obtain carbohydrates by eating foods that contain
them. In order to use the energy contained in the carbohydrates, humans
must
metabolize
, or break down, the structure of the molecule in a process that is
opposite that of photosynthesis. It starts with the carbohydrate and
oxygen and produces carbon dioxide, water, and energy. The body utilizes
the energy and water and rids itself of the carbon dioxide.
Simple Carbohydrates
Simple carbohydrates, or simple sugars, are composed of
monosaccharide
or
disaccharide
units. Common monosaccharides (carbohydrates composed of single sugar
units) include
glucose
, fructose, and galactose. Glucose is the most common type of sugar and
the primary form of sugar that is stored in the body for energy. It
sometimes is referred to as blood sugar or dextrose and is of particular
importance to individuals who have
diabetes
or
hypoglycemia
. Fructose, the primary sugar found in fruits, also is found in honey and
high-fructose corn syrup (in soft drinks) and is a major source of sugar
in the
diet
of Americans. Galactose is less likely than glucose or fructose to be
found in nature. Instead, it often combines with glucose to form the
disaccharide lactose, often referred to as milk sugar. Both fructose and
galactose are metabolized to glucose for use by the body.
Oligosaccharides
are carbohydrates made of two to ten monosaccharides. Those composed of
two sugars are specifically referred to as disaccharides, or double
sugars. They contain two monosaccharides bound by either an alpha bond or
a beta bond. Alpha bonds are digestible by the human body, whereas beta
bonds are more difficult for the body to break down.
There are three particularly important disaccharides:
sucrose
, maltose, and lactose. Sucrose is formed when glucose and fructose are
held together by an alpha bond. It is found in sugar cane or sugar beets
and is refined to make granulated table sugar. Varying the degree of
purification alters the
SUGAR COMPARISON
|
Sugar
|
Carbohydrate
|
Monosaccharide or disaccharide
|
Additional information
|
|
Beet sugar (cane sugar)
|
Sucrose
|
Disaccharide (fructose and glucose)
|
Similar to white and powdered sugar, but varied degree of
purification
|
|
Brown sugar
|
Sucrose
|
Disaccharide (fructose and glucose)
|
Similar to white and powdered sugar, but varied degree of
purification
|
|
Corn syrup
|
Glucose
|
Monosaccharide
|
|
|
Fruit sugar
|
Fructose
|
Monosaccharide
|
Very sweet
|
|
High-fructose corn syrup
|
Fructose
|
Monosaccharide
|
Very sweet and inexpensive
Added to soft drinks and canned or frozen fruits
|
|
Honey
|
Fructose and glucose
|
Monosaccharides
|
|
|
Malt sugar
|
Maltose
|
Disaccharide (glucose and glucose)
|
Formed by the hydrolysis of starch, but sweeter than starch
|
|
Maple syrup
|
Sucrose
|
Disaccharide (fructose and glucose)
|
|
|
Milk sugar
|
Lactose
|
Disaccharide (glucose and galactose)
|
Made in mammary glands of most lactating animals
|
|
Powdered sugar
|
Sucrose
|
Disaccharide (fructose and glucose)
|
Similar to white and brown sugar, but varied degree of purification
|
|
White sugar
|
Sucrose
|
Disaccharide (fructose and glucose)
|
Similar to brown and powdered sugar, but varied degree of
purification
|
|
SOURCE: Mahan and Escott-Stump, 2000; Northwestern University;
Sizer and Whitney, 1997; and Wardlaw and Kessel, 2002.
|
final product, but white, brown, and powdered sugars all are forms of
sucrose. Maltose, or malt sugar, is composed of two glucose units linked
by an alpha bond. It is produced from the chemical decomposition of
starch, which occurs during the germination of seeds and the production of
alcohol. Lactose is a combination of glucose and galactose. Because it
contains a beta bond, it is hard for some individuals to digest in large
quantities. Effective digestion requires sufficient amounts of the
enzyme
lactase.
Complex Carbohydrates
Complex carbohydrates, or
polysaccharides,
are composed of simple sugar units in long chains called polymers. Three
polysaccharides are of particular importance in human
nutrition
: starch,
glycogen
, and dietary
fiber
.
Starch and glycogen are digestible forms of complex carbohydrates made of
strands of glucose units linked by alpha bonds. Starch, often contained in
seeds, is the form in which plants store energy, and there are two types:
amylose and amylopectin. Starch represents the main type of digestible
complex carbohydrate. Humans use an enzyme to break down the bonds linking
glucose units, thereby releasing the sugar to be absorbed into the
bloodstream. At that point, the body can distribute glucose to areas that
need energy, or it can store the glucose in the form of glycogen.
Glycogen is the polysaccharide used to store energy in animals, including
humans. Like starch, glycogen is made up of chains of glucose linked by
alpha bonds; but glycogen chains are more highly branched than starch. It
is this highly branched structure that allows the bonds to be more quickly
broken down by enzymes in the body. The primary storage sites for glycogen
in the human body are the liver and the muscles.
Another type of complex carbohydrate is dietary fiber. In general, dietary
fiber is considered to be polysaccharides that have not been digested at
the point of entry into the large intestine. Fiber contains sugars linked
by bonds that cannot be broken down by human enzymes, and are therefore
![Pastas and whole-grain breads contain complex carbohydrates, which are long strands of glucose molecules. Nutritionists recommend that 55–60 percent of calories come from carbohydrates, and especially complex carbohydrates. [Photograph by James Noble. Corbis. Reproduced by permission.]](../images/nwaz_01_img0048.jpg)
Pastas and whole-grain breads contain complex carbohydrates, which
are long strands of glucose molecules. Nutritionists recommend that
55–60 percent of calories come from carbohydrates, and
especially complex carbohydrates.
[Photograph by James Noble. Corbis. Reproduced by permission.]
labeled as indigestible. Because of this, most fibers do not provide
energy for the body. Fiber is derived from plant sources and contains
polysaccharides such as
cellulose
, hemicellulose, pectin, gums, mucilages, and lignins.
The indigestible fibers cellulose, hemicellulose, and lignin make up the
structural part of plants and are classified as
insoluble
fiber because they usually do not dissolve in water. Cellulose is a
nonstarch carbohydrate polymer made of a straight chain of glucose
molecules
linked by beta bonds and can be found in whole-wheat flour, bran, and
vegetables. Hemicellulose is a nonstarch carbohydrate polymer made of
glucose, galactose, xylose, and other monosaccharides; it can be found in
bran and whole grains. Lignin, a noncarbohydrate polymer containing
alcohols and acids, is a woody fiber found in wheat bran and the seeds of
fruits and vegetables.
In contrast, pectins, mucilages, and gums are classified as soluble fibers
because they dissolve or swell in water. They are not broken down by human
enzymes, but instead can be metabolized (or fermented) by
bacteria
present in the large intestine. Pectin is a fiber made of galacturonic
acid and other monosaccharides. Because it absorbs water and forms a gel,
it is often used in jams and jellies. Sources of pectin include citrus
fruits, apples, strawberries, and carrots. Mucilages and gums are similar
in structure. Mucilages are dietary fibers that contain galactose, manose,
and other monosaccharides; and gums are dietary fibers that contain
galactose, glucuronic acid, and other monosaccharides. Sources of gums
include oats,
legumes
, guar, and barley.
Digestion and Absorption
Carbohydrates must be digested and absorbed in order to transform them
into energy that can be used by the body. Food preparation often aids in
the digestion process. When starches are heated, they swell and become
easier for the body to break down. In the mouth, the enzyme amylase, which
is contained in saliva, mixes with food products and breaks some starches
into smaller units. However, once the carbohydrates reach the acidic
environment of the stomach, the amylase is inactivated. After the
carbohydrates have passed through the stomach and into the small
intestine, key digestive enzymes are secreted from the pancreas and the
small intestine where most digestion and absorption occurs. Pancreatic
amylase breaks starch into disaccharides and small polysaccharides, and
enzymes from the cells of the small-intestinal wall break any remaining
disaccharides into their monosaccharide components. Dietary fiber is not
digested by the small intestine; instead, it passes to the colon
unchanged.
Sugars such as galactose, glucose, and fructose that are found naturally
in foods or are produced by the breakdown of polysaccharides enter into
absorptive intestinal cells. After absorption, they are transported to the
liver where galactose and fructose are converted to glucose and released
into the bloodstream. The glucose may be sent directly to organs that need
energy, it may be transformed into glycogen (in a process called
glycogenesis) for storage in the liver or muscles, or it may be converted
to and stored as fat.
Glycolysis
The molecular bonds in food products do not yield high amounts of energy
when broken down. Therefore, the energy contained in food is released
within cells and stored in the form of adenosine triphosphate (ATP), a
high-energy compound created by cellular energy-production systems.
Carbohydrates are metabolized and used to produce ATP molecules through a
process called glycolysis.
Glycolysis breaks down glucose or glycogen into pyruvic acid through
enzymatic
reactions within the
cytoplasm
of the cells. The process results in the formation of three molecules of
ATP (two, if the starting product was glucose). Without the presence of
oxygen, pyruvic acid is changed to
lactic acid
, and the energy-production process ends. However, in the presence of
oxygen, larger amounts of ATP can be produced. In that situation, pyruvic
acid is transformed into a chemical compound called
acetyle coenzyme A,
a compound that begins a complex series of reactions in the
Krebs Cycle
and the electron transport system. The end result is a net gain of up to
thirty-nine molecules of ATP from one molecule of glycogen (thirty-eight
molecules of ATP if glucose was used). Thus, through certain systems,
glucose can be used very efficiently in the production of energy for the
body.
Recommended Intake
At times, carbohydrates have been incorrectly labeled as
"fattening." Evidence actually supports the consumption of
more, rather than less, starchy foods. Carbohydrates have four
calories
per gram, while dietary fats contribute nine per gram, so diets high in
complex carbohydrates are likely to provide fewer calories than diets high
in fat. Recommendations are for 55 to 60 percent of total calories to come
from carbohydrates (approximately 275 to 300 grams for a 2,000-calorie
diet). The majority of carbohydrate calories should come from complex
rather than simple carbohydrates. Of total caloric intake, approximately
45 to 50 percent of calories should be from complex carbohydrates, and 10
percent or less from simple carbohydrates.
It is important to consume a minimum amount of carbohydrates to prevent
ketosis
, a condition resulting from the breakdown of fat for energy in the
absence of carbohydrates. In this situation, products of fat breakdown,
called ketone bodies, build up in the blood and alter normal
pH
balance. This can be particularly harmful to a fetus. To avoid ketosis,
daily carbohydrate intake should include a minimum of 50 to 100 grams. In
terms of dietary fiber, a minimum intake of 20 to 35 grams per day is
recommended.
Exchange System
The exchange system is composed of lists that describe carbohydrate, fat,
and protein content, as well as caloric content, for designated portions
of specific foods. This system takes into account the presence of more
than one type of nutrient in any given food. Exchange lists are especially
useful for individuals who require careful diet planning, such as those
who monitor intake of calories or certain nutrients. It is particularly
useful for diabetics, for whom carbohydrate intake must be carefully
controlled, and was originally developed for planning diabetic diets.
Diabetes, Carbohydrate-Modified Diets, and Carbohydrate Counting
Diabetes is a condition that alters the way the body handles
carbohydrates. In terms of diet modifications, diabetics can control blood
sugar levels by appropriately managing the carbohydrates, proteins, and
fats in their meals. The amount of carbohydrates, not necessarily the
source, is the primary issue. Blood glucose levels after a meal can be
related to the process of food preparation, the amount of food eaten, fat
intake, sugar absorption, and the combination of foods in the meal or
snack.
One method of monitoring carbohydrate levels—carbohydrate
counting—assigns a certain number of carbohydrate grams or
exchanges to specific foods. Calculations are used to determine
insulin
need, resulting in better control of blood glucose levels with a larger
variety of foods. Overall, diabetic diets can include moderate amounts of
sugar, as long as they are carefully monitored.
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The carbohydrate world can be very confusing. At times, carbohydrates are accused of being the cause of gaining weight, while other times carbohydrates are viewed as the ideal energy source for the body. Let’s take a closer look at the functions of carbohydrates:
- Carbohydrates spare protein so that protein can concentrate on building, repairing, and maintaining body tissues instead of being used up as an energy source.
- For fat to be metabolized properly, carbohydrates must be present. If there are not enough carbohydrates, then large amounts of fat are used for energy. The body is not able to handle this large amount so quickly, so it accumulates ketone bodies, which make the body acidic. This causes a condition called ketosis.
- Carbohydrate is necessary for the regulation of nerve tissue and is the ONLY source of energy for the brain.
- Certain types of carbohydrates encourage the growth of healthy bacteria in the intestines for digestion.
- Some carbohydrates are high in fiber, which helps prevent constipation and lowers the risk for certain diseases such as cancer, heart disease and diabetes.
How Carbs Turn to Fat
The digestion of carbohydrates actually starts in the mouth where an enzyme called salivary amylase starts the breakdown. The rest of the digestion process occurs mainly in the small intestine where enzymes break down large carbohydrate molecules into a simpler form called glucose. Glucose is absorbed into the blood stream and is used in several different ways:
- Much of the glucose is used for immediate energy needs by the cells.
- If there is more glucose than the cells need, then part of the glucose is stored as glycogen in the liver and muscle tissue. If blood glucose levels drop too low, the body can use this stored glycogen to replenish the supply. If levels are too high, the excess continues to be stored as glycogen.
- After energy needs are met and the glycogen stores are filled, any excess glucose can be converted to fatty acids and stored as fat tissue. The fat tissue has unlimited storage capabilities.
Fiber is also a type of carbohydrate but it has a different chemical make-up. Humans do not have the enzymes necessary to break down this type of carbohydrate. Therefore it is not digested and provides no calories or energy. Fiber gives the bulk to the intestinal contents and aids in normal elimination.
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Different Types of Carbs
One way to classify carbohydrates is by their chemical make-up:
| Monosaccharides |
Glucose |
Found naturally in fruits, sweet corn and honey. It is also the basic unit of complex carbohydrates. Glucose is the form of sugar normally found in the blood stream and used by the body for energy. |
| |
Fructose |
Found in fruits and honey. |
| |
Galactose |
Does not occur freely in nature but is produced from the breakdown of milk sugar (lactose). |
| Disaccharides |
Sucrose |
Ordinary table sugar. It is found mainly in sugar cane, sugar beets, molasses, maple syrup, and maple sugar. Sucrose if formed when glucose and fructose bond together. |
| |
Maltose |
Appears when starch is broken down by the body and also occurs in germinating seeds. It is formed when two units of glucose bond together. |
| |
Lactose |
The sugar found in milk. It is made by the combination of glucose and galactose. |
| Polysaccharides |
Starch |
Found in grains, roots, vegetables and legumes. It is made up of many (up to 1000) glucose units. Humans can digest it. One only needs to cook and chew the plant cells to break open the cellulose walls. Enzymes release the individual glucose units, which are absorbed into the blood stream. |
| |
Glycogen |
The storage form of carbohydrates in man and animals and is the primary source of glucose and energy. Muscle glycogen is used directly as energy. Liver glycogen may be converted to glucose and carried by the blood to the tissues for their use. |
| |
Cellulose |
Made up of many glucose molecules and is the supportive framework of plants. Cellulose cannot be digested by humans. Therefore, it provides bulk to the stool. Cellulose is a type of fiber. |
| |
Hemicelluloses |
Includes pectin and agar-agar. The body does not digest them. However they do absorb water, form a gel and increase the bulk of the stool, which gives a laxative effect. Pectin is found in ripe fruit and agar-agar comes from seaweed. |
| |
Fiber |
Only found in plant foods. It is the part of plants that the body cannot digest. There are two kinds of fiber, and it is important to have both kinds in the diet every day. |
Soluble fiber is found in beans, peas, lentils, oats, and barley. Some fruits and vegetables also have soluble fiber, such as apples, carrots, plums and squash. Eating foods with soluble fiber may help to lower blood cholesterol and decrease your risk of heart disease. These foods may also help lower blood sugar levels, which is important if you have diabetes.
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Insoluble fiber is found in foods like wheat bran, whole grains and all vegetables and fruits. It is often called roughage or bulk because it keeps the digestive system running smoothly. This helps with constipation, hemorrhoids, and other digestive problems. It may help to prevent some types of cancer.
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The Glycemic Index
A new system for classifying carbohydrates is the glycemic index. The glycemic index ranks foods on how they affect blood sugar level by measuring how much the blood sugar increases after one eats. For example, white bread is digested quickly into glucose, causing blood sugar to spike quickly. Therefore white bread has a high glycemic index number. In contrast, brown rice is digested more slowly, causing a lower, more gentle change in blood sugar. It therefore has a lower glycemic index number.
Diets filled with high glycemic index foods, which cause quick and strong increases in blood sugar levels, have been linked to an increased risk for diabetes and heart disease.
Using the glycemic index can be somewhat confusing. Some foods that contain complex carbohydrates, such as potatoes, quickly raise blood sugar levels, while some foods that contain simple carbohydrates, such as whole fruit, raise blood sugar levels more slowly.
The Bottom Line
The basic message is simple when it comes to selecting the amount and type of carbohydrate foods. Carbohydrates should make up 45% - 65% of the total daily calories in a healthy diet. At least 130 grams of carbohydrate should be included in the diet to prevent ketosis. Whenever possible, replace highly processed/refined grains, cereals, and sugars with minimally processed whole-grain products.
The harder your body has to work to convert the carbohydrate into glucose (and ultimately fat), the lower the food’s glycemic number. Therefore, anything that slows the digestion and absorption of a carbohydrate-containing food will lower its glycemic index. These factors include:
- Particle size. Larger particle sizes found in stone-ground flour, as opposed to finely processed flours, will slow digestion and lower the glycemic index.
- Soluble fiber. This type of fiber, found in some fruits, vegetables, legumes, oat bran, and oatmeal, slows digestion and lowers the glycemic index.
- Fiber coverings. Foods with a fibrous cover such as beans and seeds are digested more slowly and have a lower glycemic index.
- Acidity. The acid found in some fruits, pickled foods, and vinegar slow digestion and lowers the glycemic index.
- Type of starch. Starch comes in many different configurations. Some are easier to break into sugar molecules than others.
- Ripeness. Some ripe fruits and vegetables tend to have more sugar than unripe ones, and so tend to have a high glycemic index.
- Fat. Fat slows digestion and lowers the glycemic index.
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Notes Carbohydrates
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