Carbohydrates: Functions, Recommended Intake, Deficiency

What are Carbohydrates?

Carbohydrate is a macronutrient. Carbohydrates are made by green plants during a process called photosynthesis. The plants use energy from sunlight to turn water (from the soil) and carbon dioxide gas (from the air) into carbohydrate, which they store in their roots, stems, fruits and leaves.

The energy is ‘trapped’ in the carbohydrate so when we eat it, the energy is released in our bodies. This means that plant foods are the most important sources of carbohydrate. There are two main types:

  • sugars
  • complex carbohydrates.


Sugars are the simple units (molecules) from which all carbohydrates are made. There are two groups of sugars with different types in each.

Sugar group Individual sugars Foods which supply them
Simple sugars

Chemical name:


Fructose Fruits, plant juices, honey
Glucose Vegetables, fruits (especially when ripe), sugar used in cooking
Galactose Milk
Double sugars

Chemical name:



Made from

1 unit of glucose


1 unit of fructose

fruits and vegetables

Sugar cane and sugar beet (made into caster sugar, granulated sugar, brown sugar, etc.), also found in some

Made from:

1 unit of glucose


1 unit of galactose

Milk and some milk products such as yogurt

Made from:

1 unit of glucose +

1 unit of glucose

Cereal plants such as barley, and added to products such as malted biscuits, malted milk drinks

Complex Carbohydrates

Complex carbohydrates are made up of long ‘chains’ (molecules) of glucose units all joined together in different ways. There are five main groups of complex carbohydrates, which are also known as polysaccharides. Polysaccharide means ‘poly’ = many + ‘saccharides’ = sugars

Polysaccharide name What it is and what it does Foods which are good sources
  • The main energy store for plants
  • Broken down during digestion to glucose units and used for energy in the body
  • Root vegetables (e.g. carrots, parsnips), potatoes, yams, plantains, bananas, cereals (rice, wheat, millet, oats), cereal products (e.g. bread, pasta, pastries, biscuits, breakfast cereals), lentils, beans, seeds
Dietary fibre

Chemical name: non-starch polysaccharides (NSP)

  • The parts of a plant that give it strength and structure
  • Includes cellulose and gums
  • Cannot be digested by the body
  • Helps the body to get rid of solid waste products (faeces)
  • Whole grain cereal foods (e.g. whole wheat, brown rice, oats), whole grain cereal products (e.g. bread, pasta, breakfast cereals, wheat and oat bran), seeds, beans, lentils, fruits and vegetables (especially leaves and stems)
  • Makes a gel in products such as jam so that the jam sets
  • Cannot be digested by the body
  • Helps the body to get rid of solid waste products (faeces)
  • Some fruits (e.g. plums, apricots, damsons, apples)
  • Formed during the baking and toasting of starchy products
  • Broken down during digestion to glucose units and used for energy in the body
  • Toasted bread, the crust on cakes, bread, pastries
  • Formed in the body in the liver from the digestion of carbohydrates
  • Stored in the liver and muscles as a supply of energy
  • Made in the body

Functions of Carbohydrates

It’s hard to deny that carbohydrates play an important role in the human body, regardless of where you fall on this debate.  Below are the key functions of carbohydrates:

1. Supply your body with energy

Energy is one of the primary functions of carbohydrates.

Before entering the bloodstream, carbohydrates in foods are digested and broken down into glucose.

In cellular respiration, glucose in the blood is taken up into your cells and used to produce adenosine triphosphate (ATP), a fuel molecule. ATP can be used by cells for a variety of metabolic functions.

2. Provide stored energy

The body can store excess glucose if it has enough glucose to meet its current needs.

Glucose is stored in the liver and muscles as glycogen.

There are approximately 100 grams of glycogen in the liver. In between meals, these glucose molecules can be released into the blood to provide energy throughout the body.

3. Help preserve muscle

You body uses glucose storage to ensure that it has enough glucose to carry out all of its functions.

For energy, muscle can also be broken down into amino acids and converted into glucose or other compounds when glucose is lacking from carbohydrates.

Muscle cells are crucial to body movement, so this situation isn’t ideal. The loss of muscle mass has been associated with poor health and a higher death rate

4. Promote digestive health

Dietary fiber does not break down into glucose like sugars and starches.

The body does not digest this type of carbohydrate. There are two main types of fiber: soluble and insoluble.

Oats, legumes, and the inner parts of fruits and vegetables contain soluble fiber. As it passes through the body, it draws in water and forms a gel-like substance. Making your bowel movements easier is made easier by increasing the bulk of your stool and softening it.

5. Influence heart health and diabetes

You may develop diabetes if you consume excessive amounts of refined carbs.

Dietary fiber, however, can be beneficial to your heart and blood sugar levels.

In the small intestine, viscous soluble fiber binds to bile acids and prevents them from being reabsorbed. Blood cholesterol is used by the liver to make more bile acids.

Recommended Carbohydrate Intake

The DRI committee advises that carbohydrates should contribute about half (45 to 65 percent) of the energy requirement. A person consuming 2000 kcalories a day should therefore obtain 900 to 1300 kcalories’ worth of carbohydrate, or between 225 and 325 grams. This amount is more than adequate to meet the RDA for carbohydrates, which is set at 130 grams per day based on the average minimum amount of glucose used by the brain.

When it established the Daily Values that appear on food labels, the FDA used a guideline of 60 percent of kcalories in setting the Daily Value for carbohydrates at 300 grams per day. For most people, this means increasing total carbohydrate intake. To this end, the Dietary Guidelines for Americans encourage people to choose fiber-rich whole grains, vegetables, fruits, and legumes daily.

Deficiency of Carbohydrate

The body must have a constant supply of energy. It can also get energy from fat and protein foods but prefers to use carbohydrates. If we do not eat enough carbohydrates, our bodies will use fat from our food intake and body stores, and we will lose weight. If there is still not enough from these sources, protein from the muscles will be broken down and converted to energy, but this is not good for the body and will weaken it.

In areas of the world where there are long-term food shortages and people suffer from famine, it is a common sight to see very thin people with little or no muscle on their bodies.

People who are training to take part in sports activities have to make sure that they have enough glycogen stored in their liver and muscles before they exercise. If they do not have enough, their muscles will run out of energy, they will start breaking down fat for energy (which is a much slower process), and will suffer from severe fatigue (tiredness) which is known as ‘hitting the wall’. To prevent this, athletes must make sure they load their body with carbohydrates in the days before a sporting event so that their liver and muscle glycogen stores are full.

Side Effects of Too Much Carbohydrates

If we eat too much carbohydrates and do not use up the energy we have eaten, the body will store the excess energy from the carbohydrate as fat in a special tissue called adipose tissue under the skin.

Consuming too many carbohydrates or too much of the wrong type of carbohydrates leads to the following health problems.

Tired Feeling

Blood sugar levels spike rapidly when you consume simple carbohydrates such as candy, cookies, crackers, fruit and vegetables, soft drinks, energy drinks, and fruit drinks. When blood sugar spikes rapidly, an energy crash usually follows within a few hours.


A high-carbohydrate diet increases caloric intake and causes obesity. A survey published in the February 2004 issue of the Centers for Disease Control and Prevention’s “Morbidity and Mortality Weekly Report” found that between 1971 and 2000 women’s daily caloric intake increased by 22 percent and men’s by 7 percent. This increase is primarily due to carbohydrate intake. 

Gastrointestinal Distress

The amount of gastrointestinal distress you experience may be exacerbated by carbohydrate intake. Carbohydrate digestion causes more gas than any other type of food, including fat, according to the National Digestive Diseases Information Clearinghouse. Gas builds up in the digestive tract, causing abdominal discomfort, belching, bloating, and flatulence.

Triglyceride Levels

Added sugars, such as those added during food processing and those added before consumption, may increase cholesterol levels. Circulation, a journal published by the American Heart Association, reports that diets high in fructose, glucose, and sucrose often result in high triglyceride levels. Increased risk of heart attack and stroke is associated with triglycerides, a type of cholesterol that builds up in your arteries.

How to Reduce Carbohydrate Intake

Carbohydrates are typically found in diets that include sugary snacks, chips, refined grains, and high-calorie drinks. The 2010 Dietary Guidelines for Americans recommend consuming more naturally occurring carbohydrates, such as whole grains, vegetables, lentils, and fruits while reducing your intake of processed foods with added sugar. 

You can reduce your desire for high-carbohydrate snacks and overeating during meals by eating high-fiber foods. 

You can also eliminate more carbohydrates from your diet by eliminating liquid calories such as soft drinks, fruit drinks, and energy drinks.

Leave a Comment