Understanding Carbohydrates

The last of the macronutrients to turn our attention to are carbohydrates. The main function of carbohydrates is to provide energy, and the majority of cells in the body will use carbohydrates and fats for this purpose. Only using protein when carbohydrates are limited for this purpose. Indigestible carbohydrates, known as fibre, are also critical for aiding gut function and health. 

The government guidelines regarding nutrition recommend that the majority of our diet should be from carbohydrates, around 50-60%. However, I would take this figure with a pinch of salt - pun intended. While the total amount of carbohydrate intake will vary among person to person, an individual’s goals and the quality of carbohydrates should take precedence. As I’ve spoken about in other posts, when calculating macronutrient targets for clients, I always base the initial figure on on protein intake (between 2 and 2.8g per kg of lean mass in most cases), then factor in the fat intake, while the remainder of calories will be made up of carbohydrates. Now, in some cases, this will be about 50% of calories, but the total number and percentage will always depend on energy requirements, and how the individual responds to the first two factors. 

Carbohydrates are always converted into glucose by the body, to be used by cells. The stored form of glucose - glycogen - can then be stored directly in the muscles and in the liver. In excess consumption, where the body does not immediately require glycogen, excess glucose is stored as body fat.

All carbohydrates are made up of molecules called saccharides divided into three categories: simple carbohydrates (sugars); complex carbohydrates (starches); and non-starch polysaccharides (NSP) or  fibre. 

Simple carbohydrates can be classified into two groups as monosaccharides, a single unit of sugar: either glucose, fructose or galactose. Or as disaccharides of two sugar units joined together: Sucrose (glucose + fructose), Lactose (Glucose and galactose), Maltose (two glucose molecules). 

Sources of simple carbohydrates also fall into two categories of ‘unrefined’ and ‘refined.’ Unrefined carbohydrates contain fructose and glucose in varying amounts, as well as vitamins, minerals and high levels of dietary fibre. Refined carbohydrates contain very little in the way of nutrients, as well as high levels of sugar. This is important to remember that in order for energy within simple carbohydrates to be released, vitamins and minerals have to be present. Fresh fruits naturally contain the vitamins and minerals needed for the release of energy. Whereas refined and processed foods, while still providing energy, lack the required vitamins and minerals. In this regard, they can be classed as ‘anti-nutrient.’ More on this concept later.

A second form of carbohydrates, complex carbohydrates, can also be defined as unrefined or refined, and are characterised through long and complex chains of glucose molecules. Sources of unrefined complex carbohydrates include wholemeal or wholegrain products, fresh and frozen veg, and pusles and all have similar nutritional profiles to simple carbohydrates. Whereas refined carbohydrates are manufactured containing processed products. Think cakes, biscuits and white rice. Little or no vitamins are present due to the manufacturing process, and adversely affect the body’s insulin response. The insulin response of carbohydrates is ranked in the Glycemic Index of foods, developed by Dr David Jenkins in 1981. It is a ranking system given to carbohydrate foods based on how quickly their sugars are released and absorbed into the bloodstream. The quicker the carbohydrates are broken down into glucose and absorbed the higher the GI ranking, alternatively the slower the release of glucose and absorption the lower the GI ranking.

The final form of carbohydrates to discuss, and a form that is essential to gut health and digestive function, is fibre. Basically the skeleton of plants, fibre is found in the outer walls of plants and seeds. Fibre is therefore abundant in unrefined foods. While not providing an energy source, fibre assists in the transportation of foods through the digestive tract and comes in two forms: insoluble and soluble. 

Insoluble fibre is the outer protective layer of plants. It can be found in wheat bran, whole grains and cereals along with a wide range of fruit and vegetables. It holds water in the digestive tract, increasing bulk and stimulates the muscles of the digestive tract to contract, which helps to maintain strength and tone. A healthy digestive system may help to prevent conditions such as constipation and in preventing the development of colon cancer.

Soluble fibre It is normally found in the inner part of plants. It can be found in oats, beans, barley, broccoli, apples and other legumes. It is not fully known how the exact mechanism of soluble fibre works within the digestive tract; it is believed that it helps with the reduction in cholesterol by binding with fats in the digestive system and excreting them with faeces. Dietary fibre also assists in weight management as it can delay gastric emptying and lowering the glycemic index of high and moderate glycemic index foods. This helps individuals to feel fuller for longer and creates a slow and steady release of sugar (glucose) into the bloodstream. 

To conclude, carbohydrates are critical to the body as an energy source, although an excessive consumption can lead to the body storing the excess glucose as body fat. However, ensuring that the bulk of your carbohydrates come from unrefined sources helps to ensure that the appropriate levels of fibre are present in the diet. This can ensure that metabolic health is maintained. If you have any comments or questions, or if you want me to discuss any aspects of these posts in more detail, then please leave a comment below.