Carbohydrates are a major source of energy for cells and activities within the cells, which means they provide energy for the entire body.
They are commonly known as sugars and starches and are organic compounds made up of carbon, hydrogen, and oxygen.
They are also the major source of energy for cells and cellular activities and for providing energy for a person’s entire system.
In terms of foods, some of the best sources of carbohydrates are legumes, grains, potatoes, and many vegetables and fruits.
Why are carbohydrates a major part of the human diet?
All human cells have evolved so that carbohydrates are the body’s primary energy source. In fact, the body’s entire metabolic system begins with glucose. In general, the digestive system changes carbohydrates into glucose, which is then used for energy for cells, tissues, and all the body’s organs.
Which is a better source of energy for the body, carbohydrates or fat?
In general, fats contain nine kilocalories (indirectly, a form of energy) per gram, while carbohydrates average about four kilocalories per gram.
Thus, fats are useful for storing energy, but sugars are easier to break down during metabolism.
But no one truly agrees which source of energy is “better.” Perhaps the answer lies in individual situations.
For example, babies require fat in their diets for both energy and to build a healthy nervous system, whereas many middle-aged adults often consume too much fat for their body’s metabolic requirements, often leading to their becoming overweight.
Foods rich in carbohydrates are a staple of people’s diets because glucose is a main source of energy.
Why is the role of carbohydrates in the human diet so highly debated?
T he role of carbohydrates in our diet is a hotly debated subject, and the reason why is clear: Many popular diets, especially a low-carbohydrate diet, propose that the only way to lose weight is to eliminate carbohydrates.
Because of such “trend” diets, for many people, the word “carbohydrate” has become inherently bad.
But there seems to be more of a case for the other side.
Carbohydrates are fuel for the brain, nervous system, muscles, and various organs.
In fact, they are more high-quality fuels than fats and proteins, mainly because it takes little for the body to break them down and release their energy.
Thus, the body metabolizes these simple carbohydrates (sugar) and starches into glucose (blood sugar), which becomes the body’s primary fuel source, as long as carbohydrates are eaten in moderation.
Is fiber a form of carbohydrate?
Yes, fiber is another form of carbohydrate, one that has many major health benefits. For example, whole grains are important for reducing the risk of colon cancer and keeping the body’s digestive tract in good working order. Many long-term studies have shown that a diet with the most whole grains and cereal fibers, especially nutrient-rich grains and fibers that are less milled or processed, can provide protection from certain cancers, heart disease, and even type 2 diabetes.
How were carbohydrates once classified, and why was the classification changed?
In the past, carbohydrates were classified as being simple or complex.
The simple carbohydrates were considered to be those composed of sugar, such as glucose and fructose.
They were the carbohydrates that because of their simple structure were easily and quickly used in the body for energy, increasing blood glucose and insulin secretions.
They were also known as carbohydrates that could have negative health effects.
The complex carbohydrates were those with the more complex chemical structures, with three or more sugars linked together.
They were considered to be foods that contained fiber, vitamins, and minerals and took longer to digest, thus causing blood glucose to rise more slowly.
Not all the complex carbohydrates were nutritious, either, especially such foods as white bread and potatoes, which contain mostly starch.
The reason for the change in classification was that these two divisions did not account for the effect of carbohydrates on blood glucose levels and chronic diseases. Therefore, more minute divisions of carbohydrates have been developed to indicate how these organic compounds affect the body. The glycemic index, and later the glycemic load, were developed to better represent carbohydrates, foods, and the body.
How are carbohydrates currently classified?
In recent years, carbohydrates have been classified in several different ways.
For example, they are classified by their overall length (monosaccharide, disaccharide, and polysaccharide), and often these classifications are broken down into smaller units.
Thus, monosaccharides (single-unit sugars) are further grouped by the number of carbon molecules they contain, including triose (three carbon molecules), pentose (five), and hexose (six).
Carbohydrates are also classified by function.
For example, storage polysaccharides (glycogen and starch), which store energy, and structural polysaccharides (cellulose and chitin) are both categorized based on function.
What are some of the uses of carbohydrates by the body?
Various carbohydrates have different functions in the human body. The following chart identifies some common carbohydrates, some associated with diabetes, others not, and their general functions:
Carbohydrate Name
Type
General Function in the Body
Deoxyribose
monosaccharide
DNA (deoxyribonucleic acid) is a major constituent of hereditary material
Ribose
monosaccharide
Constituent of RNA (ribonucleic acid)
Fructose
monosaccharide
Important in cellular metabolism
Galactose
simple monosaccharide
Found in brain and nerve tissue
Glucose
monosaccharide
Main energy source for the body’s cells
Lactose
simple disaccharide
Milk sugar; helps the absorption of calcium
Sucrose
simple disaccharide
Produces glucose and fructose
Cellulose
polysaccharide
Not digestible but is an important fiber that provides bulk for the proper movement of food through the intestines
Glycogen
polysaccharide
Stored in the liver and muscles until needed as an energy source and is then converted to glucose
Heparin
polysaccharide
Prevents excessive blood clotting
What are some sources of the various carbohydrates and their effect on blood glucose levels?
There are numerous sources for the various carbohydrates, some that raise a person’s blood sugar rapidly and others that do so slowly. The following lists the name of the carbohydrate, type of carbohydrate, how fast it raises blood glucose levels, and which foods contain the carbohydrate (note: two starches in this list have a different response in the body, depending on whether it is a straight- or branched-chain type of starch):
Dairy products such as milks and cheeses contain the sugar lactose, which will raise blood sugar, but it will do it more slowly than maltose or fructose.
Maltose , Maltose, or malt sugar, is a simple disaccharide made up of two glucose units; thus, it raises blood glucose levels extremely fast. It is produced during the breakdown of starches.
Dextrose , Dextrose is a simple disaccharide that raises the blood glucose levels very rapidly; it is found in many candies and in diabetic products, such as those meant to treat hypoglycemic events (also known as glucose tablets).
Sucrose , Sucrose is a simple disaccharide that raises blood glucose levels quickly; it is found in simple table sugar and in fruits, vegetables, and grains.
Starch , Starch is a straight chain and is made up of long chains of glucose; it raises the blood glucose levels swiftly and is found in potatoes, rice, bread, and cereals.
Fructose , Fructose is a simple monosaccharide that raises the blood glucose levels moderately quickly; it is found in such foods as table sugar, fruit, molasses, and honey.
Lactose , Lactose, also called milk sugar, is a simple disaccharide; it raises blood glucose levels slowly. It is found in milk and dairy products.
Galactose , Galactose is a simple monosaccharide that raises blood glucose levels slowly; it is found in milk and dairy products.
Starch , Starch (a different one than listed above) is a branched chain that raises blood glucose levels very slowly; it is found in legumes and pastas.
Fiber , Fiber is a complex polysaccharide that raises blood glucose levels very slowly; it is found in fruits, vegetables, and legumes.
Why are carbohydrates a highly debated subject in the context of type 2 diabetes?
Carbohydrates are definitely a debated subject when it comes to type 2 diabetes.
In particular, some researchers suggest that it is actually an overabundance of carbohydrates in the diet that leads to people’s being excessively overweight.
They believe that the ups and downs of glucose levels after carbohydrate ingestion eventually cause the pancreas to “wear out,” or stop functioning well, leading to type 2 diabetes. (For more about this controversy, see the chapter “Diabetes and Obesity.”) But overall, recent research has shown that people develop type 2 diabetes for many reasons.
DIABETES, FIBER, AND FATS
What is fiber?
Fiber (also called dietary fiber) is a type of carbohydrate that cannot be broken down by digestive enzymes.
Because of this, fiber passes through the digestive tract more quickly, aiding in elimination.
There are two basic types of fiber: insoluble and soluble.
The insoluble fibers help to move food through the digestive tract, while the soluble fibers help to slow down food in the digestive tract.
Because both types of fiber absorb water, in most cases, they help treat and prevent constipation.
The soluble fibers dissolve in water and stick together.
Fibers include such foods as oatmeal, oat bran, lentils, barley, and even pectin-rich fruits such as apples and strawberries.
Insoluble fiber does not dissolve in water; it passes through the digestive system chewed but otherwise unchanged.
Insoluble fibers include such foods as the edible skins of many fruits (such as apples, pears, and peaches), wheat bran, brown rice, and whole-wheat products.
What are fibrous carbohydrates?
Fibrous carbohydrates are not like sugar or starch carbohydrates, as the body cannot use them for energy, but they are still important for the body’s overall health. In fact, “fibrous carbohydrate” is merely another name for “fiber.” (For more about carbohydrates, see this chapter.)
What is the difference between a lipid and a fat?
These two terms are often confused. In reality, “fats” are a category of lipids, but everyone uses the terms interchangeably. Lipids are bio-organic molecules that are hydrophobic (they do not mix with or dissolve in water), but they can be dissolved in certain organic solvents such as ether, alcohol, and chloroform. Besides fats, lipids include oils, phospholipids, steroids, and prostaglandins.
Why are fats important to the human body?
Fats are energy-rich molecules that are used as an internal source of energy for the body. They are stored in the form of triacylglycerols, or what are commonly known as triglycerides (for more about triglycerides, see the chapter “How Diabetes Affects the Circulatory System”). Fats also provide the body with insulation, protection, and cushioning (especially of the body’s organs) and help the body absorb certain vitamins, including vitamins A, D, E, and K.
Bacon, eggs, and grease all contain lots of saturated fats, increasing the bad LDL cholesterols in the blood when consumed. This, in turn, can lead to insulin resistance and glucose intolerance.
What is the difference between saturated and unsaturated fats?
Saturated fats are solid at room temperatures (except palm, palm kernel, and some coconut oils) and include most animal fats (meat, poultry, eggs, and dairy, such as beef, butter, and cheeses). Saturated fats are often associated with raising blood cholesterol. This usually occurs because saturated fats interfere with the removal of cholesterol from the blood.