The Nutrition Academy: Food Groups Carbohydrates

The Nutrition Academy: Food Groups Carbohydrates


Carbohydrates are the most abundant of the four major classes of biological molecules that make up the body, which are:


Carbohydrates provide the body with the energy and energy storage to allow metabolic functions to:

  1. Build new molecular structures
  2. Rebuild and repair existing structures within the body


The Chemical Composition of Carbohydrates 

Carbohydrates are biological molecules that consist of:

  • Carbon
  • Oxygen
  • Hydrogen



Monosaccharides (meaning: one sugar) are the simplest carbohydrate molecules.

Larger, more complex carbohydrates are formed by connecting two or more monosaccharides together.

Monosaccharides and Disaccharides 

Monosaccharides and disaccharides (meaning: two sugars; two connected monosaccharides units) are more commonly known as sugars.

Sugars are sweet tasting and serve to provide the body with energy and carbon molecules. They provide carbon because the breakdown of monosaccharides yields carbon.


Glucose is the most abundant monosaccharide. And it is the most important, as it fuels metabolic processes that produce oxygen within the body; particularly the brain.

If blood glucose levels are low, there is marked impairment in brain function.


Polysaccharides (meaning: many sugars) are complex carbohydrate molecules that are made up of more than two monosaccharides units.

Given this chemical make-up, it’s no surprise that polysaccharides molecules function as storage molecules.

Within plants, polysaccharides also function by structuring the walls of cells. The polysaccharide that is used for this purpose is known as cellulose.

Humans can’ t digest cellulose, so when plant cells are digested, the cellulose moves through the body aiding digestion. In this capacity, we refer to cellulose as fibre.

Simple Carbohydrates

What are simple carbohydrates?

Simple carbohydrates are the monosaccharides and disaccharides that we often refer to as sugars.

They are referred to as “simple” because they only contain one or two monosaccharide units. This makes them more chemically simple than other carbohydrates.

Given that simple carbohydrates (often referred to as simple sugars) need little digestion due to their chemical simplicity, they are readily available to be used as a sources of energy within the body.

The function of Simple Carbohydrate

Simple carbohydrate are primarily used as sources of energy within the body.

However, they also serve as building blocks of other biological chemicals.

For instance, nucleic acids contain monosaccharides, and nucleic acids are the backbone of DNA, which is the primary source of life.

similarly, the breakdown of glucose (the most abundant monosaccharides) into carbon dioxide and water produces the energy that allows all metabolic functions to happen.

However, large amounts of simple sugar can create and imbalance. This has poor health and dietary side-effects.

Because simple sugars can be processed and enter the bloodstream so quickly, consuming them in large amounts can create a “sugar rush”; a short-lived high-energy feeling that is shortly followed be a “crash”.

The “crash” is a lack of energy brought on by the rapid pace with which simple sugars are processed within the body, leaving the blood stream as fast as they entered it.

Dietary Considerations

The high-energy feeling that is brought on by consuming simple sugars is a pleasant feeling to most people.

However, the crash that follows a “sugar high” is unpleasant, and many people seek to rid themselves of the unpleasant feeling by eating more food high in simple sugars.

This can have health consequences, as foods that contain simple sugars often lack nutritional value and are very high in calories.

Complex Carbohydrates

What are complex carbohydrates?

Complex carbohydrates are biological molecules composed of two or more monosaccharide units.

Complex carbohydrates are often referred to as:

  1. Starches
  2. Fibrous Carbohydrates


Due to their composition, complex carbohydrates (complex sugars) function as energy storage and supply.

The function of Complex Carbohydrates

If complex carbohydrates enter the body when it is in need of immediate energy, the complex sugar will be broken down into monosaccharide sub-units and used right away as a source of energy.

If the body has sufficient energy available, the complex sugar will be converted to glycogen and stored in the muscle and liver to be accessed when energy is needed once again.

The amount of glycogen that is stored away is not a long-term supply; glycogen stores will run out after approximately one day if they are not replenished by food consumption.

Dietary Considerations 

As outlined above, complex sugars are capable of providing short-term and long-term energy supply.

This is an important dietary consideration, because foods that contain complex sugars are high in nutrients and often lower in calories.

This is important to take note of with respect to diet planning, because complex carbohydrates are more beneficial to the body overall.

Similarly, because complex carbohydrates provide energy storage, there is no “sugar rush”; energy is released when it is needed in appropriate quantities.

This is important, as sustained blood sugar levels allow an individual to function more effectively and maintain constant energy levels rather than the ups and downs of energy highs and lows.

Energy maintenance also aids in curbing craving, as the body will not signal that it needs an influx of sugar.

Dietary Sources of Carbohydrates 

Simple carbohydrates are often consumed via sources that have little nutritional value in the form of fibre or nutrients. These sources include:

  • Refined sugar
  • Honey
  • Syrups


Foods that include these sources a ingredients are often still lacking in nutritional value, and very high in calories.

Examples of foods that contain sources of simple sugars and have little nutritional value are:

  • Cakes
  • Biscuits
  • Sweets
  • Chocolate
  • Flavored and fizzy drinks
  • Heavily processed foods


Although may simple carbohydrate dietary sources have little positive benefit, there are some that contain nutrient, fibre, and water.

Some of these also have reasonable calorific content such as:

  • Fruit
  • Milk
  • Some vegetables


Consequently, in contrast with sources that have little nutritional value, these sources are less likely to produce spikes in blood sugar levels, as they contain other nutrients that work to control blood sugar spiking.

For example, the fruits and vegetables that contain simple sugars also contain fibre, and milk contains protein, both of which help maintain blood sugar levels.

Sources of Complex Carbohydrates

Complex carbohydrates are central to sound dietary planning, and are often the staples of a diet.

Sources of complex carbohydrates include:

  • Nuts
  • Seeds
  • Starchy vegetables, such a potatoes
  • Fibrous carbohydrates such as celery and broccoli


Whole grains also constitute a large portion of the complex sugar sources such as breads (particularly whole grain rather than white) and cereals such as oatmeal, weetabix and muesli (not sugary, processed cereals such as the many brands that are targeted towards children).

Legumes are rich sources of complex sugars as well; sources such as chickpeas, beans and lentils are rich in nutrient and complex sugars.

Typically, when outlining a diet plan it is important to assess the make-up of any food, even if it lies within a category that is know to be dense in complex carbohydrate sources, such as breads.

For example, most white bread has little nutritional value, so choosing bread that you want to be a quality source of complex carbohydrate, wholewheat would be a better choice.

Common Problems Associated With Carbohydrates

Blood Glucose Imbalance

This is a very common problem that you are likely to encounter on a regular basis.

To understand this problem you need to understand a bit of simple biochemistry.

The body regulates glucose its energy source in the blood very carefully. Too much glucose is dangerous and can cause cell damage, leading to nerve damage., blindness and other complaints.

This is what happens to long-term untreated diabetes.

Too little glucose is also dangerous and may cause you to feel tired, dizzy, irritable and unable to think straight. We can all feel like this if we miss a meal. In extreme cases you may faint or suffer palpitations and sweats.

The body maintains blood glucose balance by using different hormones.

When blood glucose is too high the hormone insulin is released and when it is too low, the hormone glucagon is released.

Also when levels are low the stress hormone cortisol may be released. This is linked to some of the symptoms of low blood glucose such as a racing heart and irritability.

Blood Sugar Levels

If your blood glucose levels are constantly fluctuating in extremes, this puts a strain on the body and eventually the body may not produce enough insulin or may not be responsive to insulin anymore.

This is what happens in diabetes II.

The type of carbohydrate you eat is very important for blood glucose balance. Simple sugars and foods that contain a lot of simple sugars such as sweets, cakes, biscuits, chocolate, sweet drinks, alcohol, may all raise blood glucose levels sharply, particularly if they are consumed alone or with a caffeinated drink.

This will result in release of insulin to lower the blood glucose level.

However, we are not designed to cope with lots of sweet foods and often the release of insulin in the case results in our blood glucose levels dropping to low, resulting in symptoms of low blood glucose.

These are crashes that we mentioned earlier on.

With today’s busy lifestyles, missed meals, sweet snack foods and reliance on coffee and caffeinated drinks such as a coke, many clients present with this problem.

The way to avoid this scenario, is to eat little and often, avoid too much caffeine and most importantly sway refined sweet carbohydrates for complex carbohydrates.

So swap white grains for wholegrain; cakes and biscuits for fruit and vegetables; and drink more water and herbal tea.

The Glycemic Index (GI)

One way of measuring how quickly carbohydrate food is digested and release glucose into the blood stream is to use glycemic index. Which we will discuss more in the future.

Foods which are high in the glycemic index release glucose quickly into the bloodstream. Foods that are low have a slower release and are therefore more desirable. Diabetic diets now incorporate this principle

Also many slimming diets utilize the GI.

Foods which are high GI include sweet drinks, undiluted fruit juice, white bread and baked potatoes. Foods which are low in GI include whole-grains pulses and legumes, nuts and seeds, and most vegetables and fruits.

Proteins and fats are not measured using this scale as they contain no glucose.

Carbohydrate Intolerance 

Some people are intolerance to certain types of carbohydrate. The following sections outlines some problems you may encounter.

Lactose Intolerance 

Lactose intolerance occurs when an individual lacks the enzymes (lactase) to break down lactose; a disaccharide that is present in milk and milk products.

Individuals are either born with this intolerance or may acquire it temporarily due to gastrointestinal upset. There is a higher prevalence of lactose intolerance in Asian and African populations.

Symptoms Include:

  • Abdominal pain
  • Flatulence
  • Nausea
  • Diarrhea


Treatment of lactose intolerance is predominantly dietary, and many lactos intolerant people need only cut out products such as:

  • Ice cream
  • Milk
  • Some yogurts
  • Cottage cheese


These all contain high levels of lactose.

Yet, there are many products available that are designed for lactose intolerant people. They have lactose (the enzymes lactose intolerant people are deficient in) added to them.

Live yogurt naturally contains probiotic bacteria which help break down the lactose, so some yogurt can be consumed by people who are lactose intolerant.

In the case of temporary lactase intolerance, live yogurt and probiotic supplements can be used as a treatment.

Secondary Lactose Intolerance

Secondary lactose intolerance is common and may be caused by gastrointestinal upset, e.g. food poisoning, or mal-absorption conditions such as:

  • Celiac disease
  • Stress
  • Medication (e,g antibiotic and steroid use or contraceptives)

These factors may all disrupt the gut bacteria causing an overgrowth of “bad” bacteria and not enough good bacteria or probiotics. The bacterial strain, lactobacillus, found in many live yogurts promotes lactose digestion.

Type II Diabetes 

Type II diabetes is the most common form of diabetes, and occurs when the body does not produce enough insulin, or does not react properly to the presence of insulin.

Without insulin, the body cannot properly absorb and use sugar, so it remains in the bloodstream. High blood sugar levels can ultimately lead to issues such as:

  • Kidney damage
  • Heart disease
  • Vision problems
  • Nerve damage
  • Difficulty healing
  • Delayed gastric emptying


Healthy living can decrease the risks and symptoms associated with type II diabetes.

Eating healthy, balanced meals and eating snacks consistently can minimum blood sugar levels and avoid complications related to type II diabetes.

Fibre And Water 


This is a carbohydrate that is provided solely by plant material. plant cell walls are made up of a compound called cellulose, which constitutes the bulk of dietary fibre.

Fibrous molecules are not digestible by the human body, and serve to aid in:

  • Digestion
  • Toxin Excretion
  • Reduction


Insoluble Fibre 

Insoluble fibre does not dissolve in water, which allows fibre molecules to act as an irritant in the colon, encouraging bacterial growth and in turn increasing fermentation.

This also adds bulk to solid waste, and causes it to retain some water which allows the waste to move throughout the colon more easily and avoids excess drying and compaction.

This can result in constipation and uncomfortable bowel movements.

Sources of insoluble fibre include:

  • Wholegrain
  • Vegetable
  • Fruit peel
  • Nuts
  • Seeds


Soluble Fibre

Soluble fibre dissolves in water and also aids in avoiding constipation through retaining some water in the faeces, allowing it to move through the colon more freely.

In addition, soluble fibre binds cholesterol which prevents it from entering the blood stream and contributing to heart disease.

The presence of soluble fibre throughout the digestion process maintains, a constant rate of digestion, helping to avoid spikes in blood sugar levels.

Soluble fibre can be found in:

  • Dried fruit
  • Soya products
  • Oatmeal
  • Lentils
  • Fruit
  • Vegetable


Special forms of fibre known as fructo-oligosacharides or FOS help maintain a good balance of beneficial probiotic bacteria in the lower intestines.


Water is pivotal to complete health. The average human is composed of approximately 70% water, which accounts for the dietary recommendation of drinking 6 – 8 glasses of water a day.

Water is responsible for:

  • Maintaining body temperature
  • Lubricating organs
  • Facilitating chemical reactions
  • Flushing our system of toxins
  • Providing electrolyte absorption and motility in the digestive system


Without water in the digestive system, digestion would come to a halt, as water is the means by which nutrients and electrolytes are absorbed, and waste material is transported out of the body.

In addition to the interactions that water has with biological molecules. It serves in mechanical digestive processes such as facilitating the movement of faeces through the colon.