Carbohydrates: Your Energy Source

General information

Carbohydrates, which include sugar and starch among others, are not essential, meaning the body can produce them itself (for example from amino acids). They serve as the most readily available energy source. Like protein, their energy content is 17 kJ/g (= 4 kcal/g). Carbohydrates make up by far the largest share of organic matter on the Earth's surface. Like fats, carbohydrates are made up of the elemental building blocks carbon (C), hydrogen (H) and oxygen (O) (ratio 1:2:1). However, they are water-soluble. Unlike protein, they contain no nitrogen (N).

Depending on the number of sugar building blocks, a distinction is made between simple sugars (monosaccharides), multiple sugars (oligosaccharides) made up of two to nine simple sugar units, and complex sugars (polysaccharides). Of the multiple sugars, double sugars (disaccharides) made up of two sugar units are especially important from a nutritional standpoint.

Simple sugars include glucose, fructose and galactose, which are found, for example, in fruit and honey. They are the individual building blocks for double and multiple sugars. Double sugars include, for example, milk sugar (lactose), made up of one molecule of glucose and one molecule of galactose, to which some people, particularly in Asia, are intolerant. Malt sugar (maltose), found for example in beer and made up of two glucose molecules, as well as cane or beet sugar (sucrose), found in ordinary household sugar and made up of glucose and fructose, are also double sugars. Complex sugars (polysaccharides), finally, are the storage form of sugar in the body. These are highly complex molecules made up of, in some cases, over 1000 simple sugar building blocks. In plants such as potatoes, rice and grains, the "sugar store" takes the form of starch, while in animal and human organisms it is glycogen, which is therefore often also referred to as "animal starch".

Carbohydrates in food

Carbohydrates are found almost exclusively in plant-based foods. Simple sugars such as glucose, fructose and galactose are found mainly in fruit, honey and dairy products. Important double sugars found in food include milk sugar (lactose), malt sugar (maltose), found for example in beer, and cane or beet sugar (sucrose), which is ordinary household sugar. Complex sugars are found in the form of starch, mainly in potatoes, rice and grains. Many dietary fibres (such as cellulose, see below) also belong to the carbohydrates.

Digestion and absorption

Carbohydrates are absorbed in the small intestine only in the form of monosaccharides (glucose, fructose and galactose). Before this happens, all larger carbohydrate complexes are broken down into these three monosaccharides. This takes place in the small intestine with the help of enzymes produced by the pancreas. These are the body's own catalysts, which control every biochemical reaction. Once absorbed, galactose and fructose are mostly converted into glucose in the liver, while glucose is used directly by the metabolism. Body cells absorb part of the glucose, break it down and store the remaining part in the form of glycogen in the muscles and liver, where it is only used for energy production later.

Functions in the body

Carbohydrates can only be stored in the body in small amounts. Carbohydrates are the most readily accessible energy source for the body. Simple sugars are oxidised ("burned") with the help of oxygen from the air, releasing energy in the form of heat and power. When there is a surplus in the diet, the body stores carbohydrates in the form of the water-soluble complex sugar glycogen, the counterpart to the plant storage substance starch. The main storage sites are the liver and the muscles. Liver glycogen (approx. 150 g) primarily serves to maintain blood sugar levels, while muscle glycogen (200-300 g) serves as an energy reserve. When you are intensely physically active for a short to medium duration, roughly up to two hours, full glycogen stores are of vital importance. However, these are used up after a short time during high levels of activity, which is why glycogen stores must be replenished daily. Only this way can regular, intensive activity be sustained. Getting the recommended intake of carbohydrates is therefore extremely important in sport.

The body tries to keep blood sugar (the amount of simple sugar in the blood) constant within narrow limits, in order to ensure the cells' energy supply. One example of a disruption to this regulatory mechanism is the condition diabetes mellitus. People affected must therefore control the amount of carbohydrates they consume.

Requirements

Carbohydrates are an important basic nutrient and, purely in terms of quantity, make up the main part of our diet: according to professional bodies, 50 to 60% of daily energy requirements should be covered by carbohydrates. However, a better approach than such a percentage figure is a recommendation in absolute numbers, as with protein, in grams per kg of body weight per day. How many carbohydrates need to be consumed daily depends heavily on physical activity levels. If this is low, a daily amount of 3-4 g per kg of body weight is recommended for a healthy adult. For every hour of intense physical activity, the recommended amount increases by around 1 g per kg of body weight, up to a maximum of 10 g per kg of body weight, for example for elite triathletes.

Nutritional imbalances

An insufficient carbohydrate intake can to some extent be compensated for by dietary fat. If both carbohydrates and fat are lacking as energy sources, protein is broken down instead of the normal energy carriers. Prolonged deficiency states can, for example, lead to a loss of muscle mass. An adequate carbohydrate intake, on the other hand, has a protein-sparing effect.

Excessive carbohydrate intake, on the other hand, is converted into body fat and stored in adipose tissue over the long term, once the normal storage form is exhausted, i.e. once glycogen stores are full. Weight gain is the result.