What are carbohydrates?

Humans have always received a large part of their energy in the form of carbohydrates. During digestion, carbohydrates are converted into glucose. The brain’s primary fuel is glucose, which is why carbohydrates are an important source of energy. Every day, your brain needs 150 grams of carbohydrates to function optimally.

Carbohydrates are made up of three elements: carbon (C), oxygen (O), hydrogen (H) and can be divided into four classes: monosaccharides, disaccharides, oligosaccharides and polysaccharides, as seen in figure 1. The figure illustrates the different classes of carbohydrates, with monosaccharides being the smallest because they are made up of one unit. Disaccharides are the second smallest and consist of two monosaccharides put together. The third group is oligosaccharides, which consist of 3-10 monosaccharides. Lastly, polysaccharides are among the largest carbohydrates and can consist of thousands of monosaccharides combined.

 

Below you can see the chemical structures of different carbohydrates: Figure 2 shows the chemical structure of the monosaccharide glucose, figure 3 illustrates the disaccharide maltose, while figure 4 shows the oligosaccharide raffinose and figure 5 shows a polysaccharide.

Figure 2

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Monosaccharides consist of one sugar unit and are classified as the smallest carbohydrates.

Figure 4. Oligosaccharides consist of 3-10 sugar units and raffinose belongs to this class.

Figure 3

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Disaccharides consist of two sugar units. Maltose is an example of a disaccharide.

Figure 5. Polysaccharides consist of 10 or more sugar units. Each link on the polysaccharide chain must symbolize one sugar unit.

How are carbohydrates digested?

In order for the body to absorb carbohydrates from the small intestine, they must first be broken down into the monosaccharides: glucose, fructose or galactose. This means that foods that are high in monosaccharides pass through the digestive system and into the bloodstream faster. Since disaccharides are made up of two monosaccharides, they must be split into two monosaccharides before they can be absorbed into the bloodstream. The same applies to oligo- and polysaccharides. Figure 6 shows the digestion of carbohydrates. In the mouth, salivary amylase is supplied from the salivary gland. Salivary amylase breaks down polysaccharides into oligosaccharides. In the stomach, the oligosaccharides are mixed with pancreatic amylase from the pancreas. Here they are broken down into disaccharides.

Figure 6
. Overview of enzymes that are activated during the breakdown of carbohydrates.

In the small intestine, disaccharides are broken down into monosaccharides by enzymes. To break down the disaccharide lactose, the enzyme lactase is activated, while sucrose is broken down by sucrase and so on. Figure 7 shows an overview of the enzymes used in the digestion of carbohydrates.

Once the carbohydrates are broken down into monosaccharides, they are absorbed into the bloodstream and transported to the liver. Here, the monosaccharides galactose and fructose are converted into glucose. From the liver, glucose is transported to all the body’s cells via the blood.

 

Figure 7. Carbohydrates must be broken down into monosaccharides before they can be absorbed into the bloodstream. Monosaccharides do not need to be broken down and can be absorbed directly. For larger carbohydrates, the breakdown into oligosaccharides starts in the mouth, where the salivary gland secretes the enzyme salivary amylase. Oligosaccharides are broken down into disaccharides via pancreatic amylase. Specific enzymes in the small intestine break down the disaccharide into monosaccharides, which are absorbed into the bloodstream.

What is blood sugar?

Glucose is commonly referred to as glucose. As mentioned, glucose is transported around the body with the blood and the amount of glucose in the bloodstream is known as the blood glucose level. Often blood glucose levels are simply referred to as blood sugar. After a meal it will be high and similarly, it will be low between meals.

Blood sugar after meals

The glucose concentration in the blood drops between meals because carbohydrates are no longer being supplied from the gut. Since cells need glucose to function optimally, the liver and muscles help keep blood sugar levels stable. They contain glycogen stores.

Liver glycogen is broken down into glucose by the hormone glucagon, while muscle glycogen stores are broken down by the hormone adrenaline.

During very hard physical work, such as a marathon, glycogen stores can be depleted, and in such situations it is important that the body is supplied with plenty of carbohydrates.

Figure 8 shows an overview of the hormones that are active after a meal and between meals.

Figure 8

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If the body has excess glucose, it is converted into glycogen using insulin. If the body needs glucose, glycogen in the liver is converted to glucose by glucagon, while glycogen in muscles is converted to glucose by adrenaline.

How do different types of carbohydrates affect blood sugar?

The three types of carbohydrates (mono-, di- and polysaccharides) have different influences on blood sugar levels. They are divided into simple and complex carbohydrates. Simple carbohydrates are “fast” carbohydrates and include mono- and disaccharides. Polysaccharides belong to the complex group and are called “slow” because blood sugar levels often rise more slowly after a meal containing them. In particular, it is the polysaccharides called dietary fiber that cause a slower rise in blood sugar.

Figure 9 shows a cheetah carrying foods that cause a rapid rise in blood sugar. Next to it, a turtle carries food that provides a slower increase.

Figure 9. The cheetah illustrates fast (simple) carbohydrates; those that are quickly absorbed into the bloodstream. The turtle carries around the slow (complex) carbohydrates that take longer to absorb.

What are simple carbohydrates?

Simple carbohydrates cause large fluctuations in blood sugar levels because the body absorbs them quickly. For example, if you drink a soda or eat some candy, the carbohydrates immediately pass into your bloodstream and your blood sugar levels rise rapidly. This causes the pancreas to produce a large amount of insulin to remove the glucose from the bloodstream and blood sugar levels drop rapidly. Simple carbohydrates therefore don’t provide a long-lasting feeling of fullness, because when blood sugar levels suddenly drop again, you immediately feel hungry again. Continuing to eat a lot of simple carbohydrates can lead to obesity. The Danish Veterinary and Food Administration therefore recommends that added sugar (e.g. in soft drinks and sweets) should not exceed 10% of the daily carbohydrate intake. Figure 10 shows the difference in blood sugar increase depending on the type of carbohydrate. It can be seen here that simple carbohydrates cause such a steep drop that the curve goes below normal blood sugar levels, which is where both curves start.

 

What are the symptoms of low blood sugar?

According to the Diabetes Association, the typical symptoms of low blood sugar are sweating, tingling, dizziness and irritability.

 

 

 

What are complex carbohydrates?

Oligosaccharides and polysaccharides are complex carbohydrates. They are made up of monosaccharides combined in different ways to form complex molecules. Polysaccharides are the most abundant carbohydrate in food – especially plant-based foods such as vegetables, fruits and cereals.

As seen in figure 1, glycogen, fiber and starch are the three types of polysaccharides.

Glycogen, previously described, acts as the body’s glucose store, as glycogen is a highly branched molecule consisting of around 50,000 glucose molecules.

What is dietary fiber?

Dietary fiber belongs to the group of complex carbohydrates. The gastrointestinal tract lacks the enzymes to break down the fibers, so they are only absorbed in limited quantities. The fiber that is not absorbed passes directly into the large intestine, where some is broken down by colon bacteria. This supports good gut flora and has been shown to have many important physiological effects, including a positive impact on brain function.

Figure 12 shows the division of dietary fiber: Soluble and insoluble fiber.

Soluble dietary fiber works like a sponge. They absorb water, causing them to dilate and fill up the lower stomach, which delays gastric emptying. This provides a greater sense of satiety.

The digestive enzymes needed to break down food are also disrupted by dietary fiber, which means that carbohydrates have a harder time being broken down into glucose. When they are not broken down, the cells have a lower glucose uptake, resulting in a smaller increase in blood sugar levels.

Dietary fiber can also bind bile. This means the body has to create new bile from cholesterol. It is therefore believed that dietary fiber reduces the amount of cholesterol in the blood. High blood cholesterol levels are bad for the body as they can increase the risk of developing cardiovascular disease.

To increase your fiber intake, eat whole vegetables, whole grains and fruit.

The Danish Veterinary and Food Administration recommends a daily intake of 25-35 grams of dietary fiber. This can be achieved by eating either 3-4 slices of whole grain rye bread, 300 grams of coarse pasta, 300 grams of oatmeal or 600 grams of vegetables (especially root vegetables, cabbage and onions).

How many carbs should you eat?

The Nordic Nutrient Recommendations recommend that carbohydrates should make up 45-60% of your daily diet.

For every gram of carbohydrate you eat, an amount of energy equivalent to 17 kJ (4.06 kcal) is produced.

Think about the carbohydrates in your diet!

Since carbohydrates should make up more than half of your daily energy intake, it’s important to consider exactly which carbohydrates will benefit your body the most.

If you’re not running a marathon, carbohydrates that cause a slow rise in blood sugar are preferable. You can look at a specific value called the glycemic index (GI) to examine a food’s impact on blood sugar levels over 2 hours. A high glycemic index means that the food causes blood sugar to rise and fall again quickly. And vice versa: a low glycemic index results in a slower rise and fall – and thus a longer feeling of fullness. Figure 13 shows the glycemic index of different foods. Glucose is often used as a reference value, so the glycemic index of glucose has the highest value – 100.

In general, polysaccharides are said to cause a slower rise in blood sugar than monosaccharides. But there are differences between the individual polysaccharides. Foods high in starch and low in fiber, such as potatoes, spaghetti and white bread, cause a faster rise in blood sugar than foods high in starch and fiber, such as whole grains, root vegetables, cabbage and legumes. This can be seen in figure 13, as the high fiber foods (rye bread, All-bran flakes and kidney beans) have a very low glycemic index.

Comparing the two breakfast cereals, cornflakes and All-bran flakes, cornflakes have a much higher glycemic index. This makes sense, as cornflakes contain 3 grams of fiber per 100 grams, while All-bran flakes contain 14 grams of fiber per 100 grams. If you want to feel fuller for longer after breakfast, you should choose All-bran flakes instead of cornflakes.

 

You should therefore consider the types of carbohydrates you include in your daily meals – both to maintain your weight but also to create a healthy gut flora. The food pyramid shows that foods with a low glycemic index and high fiber such as oatmeal, hearty vegetables such as cabbage, carrots and beans, and whole grain bread should make up a large part of your daily carbohydrate intake.

Fruits are also a good source of carbohydrates and are often high in vitamins and minerals. However, fruits generally have a high glycemic index due to their natural content of fruit sugar (fructose), and therefore it is important that fruit does not make up the majority of the daily recommended carbohydrate requirement.

This subpage on carbohydrates belongs to Biotech Academy’s elementary school project
The body and diet