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Man and woman sitting at a table eating spaghetti pasta, a carbohydrate

What are carbohydrates? Everything you need to know

When you think of carbohydrates, or ‘carbs’, do you think of mashed potato, chunky bread or a big bowl of pasta? You wouldn’t be wrong – carbs have a reputation as stodgy comfort foods which are not known for being the dieter’s choice.

What are carbs exactly?

Carbohydrates are biomolecules. This means they are found in living organisms, like plants. There are three other biomolecules which make up a living organism: nucleotides, proteins and lipids (fats).

Why do we need carbohydrates?

Put simply, we need carbs to keep our bodies going. Whereas the amount and type of carbs we need are a subject of much debate, consuming some form of carbohydrates is essential to provide energy to our bodies and help us eliminate waste.

When people talk about carbs, they don’t usually specify if they are referring to sugar, starch or fibre. This is where the confusion comes from which can lead people to eliminate carbs completely from their diets (this is not advisable).

There are different types of carbohydrates. In foods, the three most common types of carbohydrates are ones you will probably recognise - sugar, starch and fibre.

What do we mean when we talk about carbohydrates?


‘Free’ sugars are the type added to food and drinks such as biscuits, cakes, chocolates, sweets and most carbonated drinks. Free sugars are also found in honey, agave, maple syrup, fruit juices and smoothies. We might think it is easy to spot a food or drink high in free sugar by its sweet taste, but beware! Many savoury sauces and soups are also very high in free sugar.

Although sugar is found naturally in fruit, vegetables and dairy products, this does not count as free sugar. Free and added sugar, rather than naturally occurring sugar, is the type that health experts say we should all cut down on as much as possible.


This category is probably what most people think of when they consider carbs. Starch is present in all plant-derived foods, including pasta, bread, potatoes, grains and cereals.


Fibre a type of carbohydrate, derived from plants, which the body cannot digest. It is present in fruit and vegetables, whole grains, beans and lentils.

Why are carbohydrates important?

Your body uses carbohydrates as its main source of energy. It breaks carbs down into glucose, which is then absorbed into your bloodstream. When it meets insulin in your blood, glucose can cross over into your body’s cells where it is used as energy. Without carbohydrates providing this readily available energy in your bloodstream, your body turns to its stored fat reserves for its energy.

While this can be a good thing in the short term, your body using fat stores as its main energy source over a longer period of time might leave you feeling:

  • low on energy
  • weak
  • dizzy
  • sick
  • tired and irritable.
Carbohydrates are also important for the fibre they provide. We all need fibre to stay healthy. People who think they should be eliminating carbs from their diets often don’t realise that not getting enough fibre can cause:
  • constipation
  • bloating
  • loose stools
  • a general feeling of sluggishness.

Without fibre, undigested food, waste products and bacteria hang around in your gut for longer without being eliminated, which can cause inflammation. Additionally, a diet lacking fibre can lead to weight gain, as without fibre to make us feel full, we are at risk of overeating. The official UK guidelines for fibre intake is 15g per day for children and 30g per day for adults.

Carbohydrates are also sources of vitamins and minerals. Starchy foods, for instance, as well as providing energy, give us nutrients such as iron, calcium and B vitamins.

What are refined carbs?

Refined carbohydrates include sugars as well as refined grains which have been processed to remove nutrients and fibre. This includes anything made from white flour (bread, pasta) and white rice as well as cereal and cereal bars. Your body converts refined carbohydrates into glucose rapidly, causing a sudden blood sugar raise, or ‘spike’ soon after eating.

Consuming refined carbs also causes you also produce insulin to allow the glucose to enter your body’s cells to be used as energy. Therefore, you will also experience an insulin spike along with your blood sugar high. Some changes in blood sugar are normal, such as a raise shortly after eating. However, your blood sugar being raised too high and too often causes the over-production of insulin in your body, which can lead to insulin resistance.

Insulin is a hormone which is produced in response to the presence of glucose in the blood, and it helps your body absorb and store the glucose safely. Insulin resistance is a problematic state where your body takes on too much glucose through diet, and therefore produces so much insulin that your cells stop responding to it, shutting down their ability to absorb and store glucose.

What are complex carbs?

Complex carbohydrates (aka ‘good carbs’) are those which are not broken down into glucose rapidly by the body. They are digested more slowly, and provide a more steady, long-lasting source of energy. Complex carbohydrates are found in whole grains bread, pasta and rice, as well as quinoa, oats and some vegetables e.g. sweet potatoes, kale, broccoli and peas.

How many carbohydrates should we have per day?

The NHS EatWell Guide recommends that more than 1/3 of your diet should be made up of starchy foods, such as potatoes, bread, rice and pasta, and more than 1/3 should be fruit and vegetables.

Last updated: 17 March 2020



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