The Macronutrients: Carbohydrate

The Macronutrients: Carbohydrate

I was talking to someone over the weekend about nutrition and the media. They mentioned that although they read about the (mostly) negative aspects of Carbohydrates‘carbohydrates’ all the time, they were still unsure of what exactly carbohydrates are, in practical terms. This article will hopefully shed a little more light on one of the macronutrients in our diets: Carbohydrate.

The word ‘Carbohydrate’ is derived from ‘carbon’ and ‘water’. Carbohydrates are sugar compounds that plants synthesise when they are exposed to light. There are three main types in our diet: 

Sugars

A monosaccharide (or simple sugar) is a carbohydrate with one unit of sugar.

For example: glucose (the main form in which carbohydrate circulates in our body) found in table sugar, honey, soft drinks and confectionery. Fructose (fruit sugar) is another simple sugar. A disaccharide is a carbohydrate with two units of sugar. For example: sucrose (table sugar) and lactose (milk sugar).

Starches

Polysaccharides, (or complex carbohydrates) have more than two units of sugar linked together. Starch is found in cereal grains including bread, flour, rice, pasta, couscous and breakfast cereals. Some fruits and vegetables especially potatoes, root vegetables and pulses contain a mixture of sugars and starches.

Fibre

Dietary fibre is a generic term for a group of carbohydrates derived from the edible parts of plants that are not broken down and absorbed by the small intestine. Root vegetables, nuts and seeds, oats, fruit, cereals and wholemeal bread are valuable sources of fibre.

Fibre cereal in heart shapeStarches and fibre sources are important to:

  • regulate blood sugar levels
  • prevent use of protein for energy (it is required for other vital functions)
  • give a feeling of fullness (assisting weight control)
  • dietary fibre helps protect against heart disease and colorectal cancer and helps prevent constipation.

All dietary carbohydrate, both sugars and starches, are ultimately converted to and absorbed into the blood in the form of glucose, to provide the body’s primary energy fuel. Simple carbohydrates digest relatively quickly whereas more complex carbohydrates take longer to break down into their individual sugar units therefore resulting in a slower rise in glycaemic (blood sugar) level and a more sustained release of energy.

Glucose in the blood is carried into cells with the help of the hormone insulin. We convert any sugar the cells do not need immediately from glucose to glycogen and store it in the liver and muscles for use at a later date. The body can store about 400g of glycogen in liver and muscle cells. This equates to about 1,800 calories.  If the diet provides more carbohydrate that it needs to replenish these glycogen stores then the excess will be converted to fat.

The majority of carbohydrate in your diet should come from foods that contain fibre and are nutrient dense. These foods include whole-grain breads, cereals, and pastas; beans and legumes; vegetables; and fruits. These foods are minimally processed, contain many vitamins and minerals, and as such will contribute to good health. Sugary foods and drinks generally do not contain many other nutrients so have them occasionally in small amounts, if at all.

Over the coming weeks I will talk about the other macronutrients: protein and fat.

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Liam Leech, BSc (Hons) Sport and Exercise Science, MSc. ANutr.

Liam Leech

BSc (Hons) Sport and Exercise Science, MSc. ANutr.

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