What are carbohydrates?

Carbohydrates , along with fat and protein, are one of the three macronutrients that provide the body with energy. They consist of carbon, hydrogen, and oxygen and are the most important energy source for the brain, muscles, and many organs.

Their main purpose is to supply the body with glucose (sugar) – the preferred "fuel" for all cells. After consumption, carbohydrates are converted into glucose and either used immediately for energy or stored as glycogen in muscles and the liver.

Carbohydrates provide 4 kcal (17 kJ) per gram and play a crucial role in performance, concentration, digestion and metabolic balance.

Types of carbohydrates

Carbohydrates differ in their chemical structure and the rate at which they are absorbed by the body.

1. Simple carbohydrates (monosaccharides & disaccharides):

  • They are quickly digested and lead to a rapid increase in blood sugar.

  • Examples: Glucose (dextrose), fructose (fruit sugar), lactose (milk sugar), sucrose (table sugar).

  • Occurrence: Sweets, soft drinks, honey, white flour products, fruit.

2. Complex carbohydrates (polysaccharides):

  • They consist of long chains of sugar molecules and are broken down more slowly.

  • They provide long-lasting energy and stable blood sugar levels.

  • Examples: starch, glycogen, dietary fiber.

  • Sources: Whole grain products, legumes, potatoes, oats, rice, vegetables.

How do carbohydrates affect the body?

1. Energy source:
Carbohydrates are the body's fastest and most efficient source of energy . The brain and nervous system, in particular, depend on glucose – it cannot be replaced by fat.

2. Glycogen storage:
Excess glucose is stored as glycogen in muscles and liver and is available again when needed, for example during exercise.

3. Support for brain function and concentration:
The brain consumes approximately 120–150 g of glucose daily, which corresponds to about 20% of the body's total energy requirements. Adequate carbohydrate intake is therefore important for mental performance and mood .

4. Digestion and gut health:
Complex carbohydrates contain fiber , which regulates digestion, promotes intestinal flora, and improves the absorption of other nutrients.

5. Metabolic balance:
Carbohydrates indirectly regulate fat and protein metabolism because they "save" protein – meaning the body does not have to break down muscle protein for energy as long as sufficient carbohydrates are available.

Benefits of carbohydrates

  • Main source of fast and sustainable energy

  • Support brain function and concentration

  • Promotes digestion and gut health (through fiber)

  • Improve physical performance

  • Support recovery and regeneration after training

  • They keep blood sugar levels stable (with complex carbohydrates)

Good vs. bad carbohydrates

Good (complex) carbohydrates:

  • Slowly digestible

  • Stabilize blood sugar

  • Long-lasting satiety

  • Examples: whole-grain bread, oatmeal, quinoa, legumes, fruit, vegetables

Bad (simple, refined) carbohydrates:

  • They cause blood sugar to rise quickly

  • Lead to cravings and energy slumps.

  • Examples: sugar, white bread, pastries, soft drinks, sweets

Recommended daily intake

According to the German Nutrition Society (DGE) , about 50–55% of daily energy intake should come from carbohydrates – preferably from whole grain products, fruit, vegetables and legumes .

With an energy requirement of 2000 kcal, this corresponds to approximately 250 g of carbohydrates per day .
Sugars and highly processed carbohydrates, on the other hand, should remain below 10% of total energy intake.

Possible consequences of a shortage or excess

Carbohydrate deficiency:

  • Fatigue, difficulty concentrating

  • Irritability, headaches

  • Breakdown of muscle protein (in long-term deficiency)

  • Reduced athletic performance

Excessive intake:

  • Weight gain (due to excess calories)

  • Fluctuating blood sugar

  • Risk of insulin resistance and metabolic disorders with excessive sugar consumption

Conclusion

Carbohydrates are the body's most important energy source and essential for the brain, muscles, and metabolism. However, quality is crucial: Complex carbohydrates from natural, fiber-rich sources provide stable energy and promote health, while refined sugars cause blood sugar spikes. A balanced diet focusing on whole grains, vegetables, and legumes provides the optimal fuel for body and mind.

Sources

  1. German Nutrition Society (DGE). (2020): Carbohydrates and dietary fiber – DGE recommendations.

  2. Slavin JL. (2013): Carbohydrates, dietary fiber, and resistant starch in human health. Adv Nutr , 4(2), 203–212.

  3. Ludwig DS, et al. (2018): The carbohydrate-insulin model of obesity: beyond “calories in, calories out”. JAMA Intern Med , 178(8), 1098–1103.

  4. Jenkins DJA, et al. (2002): Glycemic index: overview of implications in health and disease. Am J Clin Nutr , 76(1), 266S–273S.