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Fundamentals of Human Nutrition/Functions

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4.3 FunctionsEdit

Carbohydrates come in many forms – as complex or as simple, as fructose, sucrose, lactose, glucose, and maltose. Carbohydrates consist of starches, sugars, dextrins, and gums. The utmost important function of carbohydrates in the human body is to provide energy - energy for the brain, our muscles, and all the way down to our cells. In addition, carbohydrates are important for regulating our blood glucose levels, enabling the metabolism of fat, and to help prevent our protein intake from being used as our first and main energy source.

An extremely important part of the energy supplied by carbohydrates is to raise low blood glucose levels. This occurs through the breakdown of carbs by the enzyme amylase. When we eat carbohydrates, our blood stream collects the carbs and our blood sugar rises. With the introduction of insulin, our cells uptake the carbohydrates, removing them from the blood stream. However, sometimes too much insulin is introduced, and our blood sugar decreases so much that it goes low – meaning below the lower threshold. When this occurs, we then need to consume more carbohydrates – a form of sugar – to increase our blood sugar.

Carbohydrates come in the forms of complex and simple – where complex sugars take longer to activate in your system, producing less of a spike in your blood sugar, whereas simple sugars react immediately. We need the glucose from carbohydrates to supply our brain and muscles with energy. This is why when we have not eaten in hours and lack an intake in carbohydrates we become weak, faint, dizzy, and cannot function at our full potential.

Carbohydrates are the preferable method of energy formation, instead of protein or fat being used first. Fat will be utilized after the whole supply of carbohydrates has run out. Once fat has started being used due to the lack in carbohydrates, fat fragments start to clump together and form ketone bodies. Although at times the ketone bodies can be a good source of energy, they are usually more harmful than good. When the production of ketone bodies is larger than the rate of usage, ketosis occurs, which affects our bodies’ acid-base balance in a negative way. On the other hand, carbohydrates are also used in preventing the protein we consume from being used as the first source of energy. Similarly to the usage of fats, the protein we consume is used for energy when our carbohydrate glucose storage runs out. Our bodies’ protein tissues are forcibly broken down to make glucose through a process called gluconeogenesis. Gluconeogenesis is another way to help prevent low blood sugars from occurring, and forms from pyruvate, lactate, glycerol, and glucogenic amino acids.


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Lawrence, R. (n.d.). Interactions of Fat and Carbohydrate Metabolism—New Aspects and Therapies: (Section of Therapeutics and Pharmacology). Retrieved November 30, 2015, from

Whitney, E., & Rolfes, S. (2015). Understanding nutrition (14th ed.). Belmont, CA: Wadsworth.

2.3.1 Sugar and StarchEdit

Carbohydrates are sugars, starches, dextrins, and gums. Both sugars and starches are classified as saccharide. Sugar is a simple carbohydrate with the chemical composition of (CH2O)n. Most sugars form ringed structures when in solution. Generally refers to as monosaccharides and disaccharides. Starch is a carbohydrate made of multiple units of glucose attached together in a form the body can digest; also known as complex carbohydrate.(1)

Starches are a form of glucose in plants. The body converts starches and sugars into dextrin. Starches and sugars are broken down into monosaccharides and the glucose is then used for energy.

The simple sugars in foods that are most important to human nutrition are called sucrose, fructose, lactose, and maltose. The body needs the simple sugar called glucose, so these other simple sugars in food break apart in the body to become glucose which yields energy of 4Kcal per gram of carbohydrate. They do this by coming apart easily at the water connections. Starches include such foods as potatoes, cereals, wheat and other grains, and rice. Starches are complex sugars, and complex sugars break down into one of the simple sugars (maltose), and then to glucose by easily breaking apart at the water connections. Essentially, starches are sugars that merely require a few more steps to make them into glucose.

’‘’Lipid metabolism’‘’
Lipids are absorbed from the intestine and undergo digestion and metabolism before they can be utilized by the body. Most of the dietary lipids are fats and complex molecules that the body needs to break down in order to utilize and derive energy from.(2)

Short chain fatty acids enter the circulation directly but most of the fatty acids are reesterified with glycerol in the intestines to form triglycerides that enter into the blood as lipoprotein particles called chylomicrons.

Lipoprotein lipase acts on these chylomicrons to form fatty acids. These may be stored as fat in adipose tissue, used for energy in any tissue with mitochondria using oxygen and reesterified to triglycerides in the liver and exported as lipoprotein called VLDL (very low density lipoproteins).

VLDL has a similar outcome as chylomicrons and eventually is converted to LDL (low density lipoproteins). Insulin simulates lipoprotein lipase.

During starvation for long periods of time the fatty acids can also be converted to ketone bodies in the liver. These ketone bodies can be used as an energy source by most cells that have mitochondria.


1. What are sugars and starches – By Dr. Beth Gruber, published on July 29, 2003 at

2. Lipid Metabolism – By Dr. Ananya Mandal, MD, published in

3. [1]

2.3.2 FiberEdit


The current research of glucose balance is ever increasing in breadth and depth of understanding. Glucose balance is a hot topic and includes the major illnesses of obesity and diabetes. From glucose supplements, hip contemporary healthy ‘how- to’ books, notable lectures and nutritional philosophies; glucose is certainly the topic of the day. It has been a curious process to find a starting point in which to explain the central concept of glucose balance while sifting through the morass of data. This brief unscientific overview is aimed at the fundamentals of what glucose is, why we need it and a general sense of what happens when we have too little or too much of this life giving simple sugar.

Glucose Balance

Glucose is a simple sugar derived from carbohydrates in our food.[1] A steady supply of glucose provides our body with an energy source in which to support healthy functioning and life. Too much or too little glucose in our blood stream can have unhealthy effects to our body. Staying in balance supports healthy functioning.[2] Glucose balance (glucose homeostasis or blood sugar regulation) is dependent upon two hormones, glucagon and insulin.[3] The presence of these hormones regulates the absorption of glucose.[1] Insulin allows absorption of glucose and glucagon stimulates the liver to release more glucose . Our brain and muscle tissue are primary receivers of glucose and utilize it as an energy source. When glucose is not absorbed for energy use, it is deposited into fat cells as storage. A simple diagram found in a journal of Nature shows how this is coordinated between the liver, pancreas and other organs in the body.[4] Finding the right glucose balance is specific to your unique genetic disposition. Talking with your doctor can provide clues to what your balance would look like. Healthy eating practices and eating nutritionally dense foods are continually stressed throughout the research on glucose. And there is little, if at all, research finds that symptoms of an unbalanced glucose balance yield desirable outcomes for people.[5] Two major conditions with evidence pointing to blood glucose are diabetes [6] and obesity. Obesity researchers are finding how the brain senses glucose and how this is linked to obesity and metabolism.[7]

Where can we find glucose and what food choices are better for us to consume? These are both broad questions and will not be the focus of this short study. However, there can be some quick comments made to examine this question. Understanding carbohydrates and digestion of carbohydrates will aid in the choices you make.[8] Since carbohydrates are mainly found in plants, consider the fiber intake of these plant based carbohydrates.[9] It is suggested that glucose absorption can be influenced by the fiber you are consuming. And eating whole foods, fiber and all, will aid in the proper balance of glucose in most people’s diets.[10]


The body uses glucose or energy if glycogen stores are unavailable. If glycogen stores are depleted, protein is used to create glucose through the process called glycogenesis. It is important to have enough carbohydrate present in the diet to prevent the need to breakdown protein for energy.

The accumulation of ketone bodies in blood is known as ketosis. It upsets the acid-base balance in the body. The body uses glucose to make body fat when carbohydrates are consumed excessively.

Gut health
Cholesterol balance

Other Functions of Carbohydrates

Dietary fibers are the structural components of plants and are found in all plant foods such as vegetables, fruits, legumes and whole grains. The bonds between their monosaccharides cannot be broken down by digestive enzymes in the body, unlike starches. Therefore, they contribute little to no energy. Dietary fibers provide structure for plants and are not able to be broken down by human enzymes.

Soluble fibers are found in oats, legumes and citrus fruits. They are associated with protecting against heart disease and diabetes by lowering blood cholesterol and glucose levels by reducing LDL cholesterol levels. They stimulate the growth of bacteria in the stomach which helps to break down food so that it can be used as energy in the body. Soluble fibers bind with fatty acids. Stomach emptying is prolonged by these fibers. Fiber slows the absorption of glucose and facilitates the passage of food through the GI tract.

Insoluble fibers do not dissolve in water or form gels and are less readily fermented. These are found mostly in whole grains and vegetables. These fibers promote bowel movements, alleviate constipation, and prevent diverticular disease. Insoluble fiber causes toxic waste to move through the colon much faster. It helps to keep an optimal pH in the intestines to protect against diseases.

Abstract: This section looks at arguably the most important macronutrient in our diets: carbohydrates. Carbohydrates are an important part of the body as they are the primary source of energy for cells. Without them, various functions including but not limited to metabolizing energy, storing energy, sparing proteins, and building macromolecules would not be possible.

The main function of carbohydrates is to provide energy to cells throughout our body [1]. After a carbohydrate is consumed, it’s broken down into smaller units of sugar – fructose, galactose, and glucose – in the stomach and small intestine [2]. Once broken down, these sugars enter the bloodstream and travel to the liver where fructose and galactose are converted to glucose [2].

When glucose is needed immediately to provide energy to the cells, the metabolic process of glycolysis begins [3]. Glycolysis is essentially just splitting glucose and results in the products pyruvic acid and ATP. Following glycolysis, glucose is broken down in the mitochondria where one carbon and two oxygen atoms are removed to produce more energy for the cells to utilize [1]. This energy is transported to the cells in another form, thus making it useable [1].

When the body has an adequate amount of energy to support its functions, the excess glucose is stored in the muscle and liver as glycogen [1]. Usually, because the body has an adequate amount of glucose, another function of the carbohydrates is to spare proteins from having to break down as a source of energy. However, in a case where there isn’t enough glucose in the body and carbohydrate intake is inadequate, proteins are then broken down and used as a source of energy [2]. The process breaks down amino acids in muscle tissue therefore causing proteins to lose their primary role as building blocks for muscles [2].

Another important role of carbohydrates is assisting in the assembly of macromolecules [1]. The glucose that isn’t used to make energy is converted to ribose and deoxyribose, which are building blocks for RNA and DNA, as well as ATP and NADPH [1]. NADPH is a very important macromolecule that serves in various chemical reactions and protects against oxidative stress [1].

In addition to that, carbohydrates, specifically glucose, also play an essential role in the central nervous system [2]. The brain is sensitive to low levels of blood glucose because glucose is the brains only source of energy, unlike in other parts of the body [1]. A lack of carbohydrates can result in hypoglycemia, or low blood glucose, which can cause physical and mental fatigue, as well as contribute to dizziness and weakness in the body [2].

If all these functions of a carbohydrate are sufficiently met, excess glucose can also be used to make fat [1].


(1) The Functions of Carbohydrates in the Body. (n.d.). Retrieved December 1, 2015, from (Links to an external site.)

(2) (n.d.). Retrieved November 30, 2015, from

(3) Overview Metabolism. (n.d.). Retrieved December 1, 2015, from