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 source of energy 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 to produce energyor stored as glycogen in the muscles and 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 speed at which they are absorbed by the body.

1. Simple carbohydrates (monosaccharides & disaccharides):

  • Are digested quickly and cause blood sugar levels to rise rapidly.

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

  • Sources: Candy, soft drinks, honey, white flour products, fruit.

2. Complex carbohydrates (polysaccharides):

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

  • Provide long-lasting energy and stable blood sugar levels.

  • Examples: Starch, glycogen, fiber.

  • Sources: Whole grains, legumes, potatoes, oats, rice, vegetables.

How do carbohydrates work in 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 stores:
Excess glucose is stored as glycogen in the muscles and liver and is available again when needed, such as during exercise.

3. Supporting the brain and concentration:
The brain consumes about 120–150 g of glucose each day, which accounts for about 20% of total energy needs. Adequate carbohydrate intake is therefore important for mental performance and mood.

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

5. Metabolic balance:
Carbohydrates indirectly regulate fat and protein metabolism because they “spare” protein - that is, the body does not need to break down muscle protein for energy as long as enough carbohydrates are available.

Benefits of carbohydrates

  • Main source of quick, sustained energy

  • Support brain function and concentration

  • Promote digestion and gut health (through dietary fiber)

  • Improve physical performance

  • Support recovery and regeneration after exercise

  • Keep blood sugar levels stable (in the case of complex carbohydrates)

Healthy vs. unhealthy carbohydrates

Healthy (complex) carbohydrates:

  • Slow to digest

  • Stabilize blood sugar

  • Keep you feeling full for longer

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

Unhealthy (simple, refined) carbohydrates:

  • 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.

For an energy requirement of 2,000 kcal, this corresponds to about 250 g of carbohydrates per day.
Sugar and highly processed carbohydrates, on the other hand, should make up less than 10% of total energy intake.

Possible effects of deficiency or excess

Carbohydrate deficiency:

  • Fatigue, difficulty concentrating

  • Irritability, headaches

  • Muscle protein breakdown (with long-term deficiency)

  • Reduced athletic performance

Excessive intake:

  • Weight gain (with excess calorie intake)

  • 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 are essential for the brain, muscles, and metabolism. However, quality is crucial: Complex carbohydrates from natural, fiber-rich sources provide stable energy and support good health, while refined sugars put a strain on blood sugar levels. A balanced diet focused 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.