What are carbohydrates?

Carbohydrates are one of the three macronutrients that provide the body with energy, alongside fat and protein. 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 provide 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):

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

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

  • Sources: 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 a stable blood sugar level.

  • Examples: Starch, glycogen, fiber.

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

How do carbohydrates work in the body?

1. Energy source:
Carbohydrates are the fastest and most efficient source of energy for the body. 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 approximately 120–150 g of glucose daily, which corresponds to about 20% of total energy requirements. Sufficient carbohydrate intake is therefore important for mental performance and mood.

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

5. Metabolic balance:
Carbohydrates indirectly regulate fat and protein metabolism because they “spare” protein - i.e., the body does not have to break down muscle protein to produce energy as long as sufficient carbohydrates are available.

Benefits of carbohydrates

  • Main source of quick and sustained energy

  • Support brain function and concentration

  • Promote digestion and gut health (through dietary fiber)

  • Improve physical performance

  • Support recovery and regeneration after training

  • Keep blood sugar levels stable (with complex carbohydrates)

Good vs. bad carbohydrates

Good (complex) carbohydrates:

  • Slow to digest

  • Stabilize blood sugar

  • Keep you feeling full for longer

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

Poor (simple, refined) carbohydrates:

  • Cause blood sugar to rise quickly

  • Lead to cravings and energy dips

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

Recommended daily intake

According to the German Nutrition Society (DGE), approximately 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.
Sugar and highly processed carbohydrates, on the other hand, should account for less than 10% of total energy intake.

Possible consequences of a deficiency or excess

Carbohydrate deficiency:

  • Fatigue, difficulty concentrating

  • Irritability, headaches

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

  • Reduced athletic performance

Excessive intake:

  • Weight gain (with a calorie surplus)

  • Fluctuating blood sugar

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

Conclusion

Carbohydrates are the body's most important source of energy and are 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 strain blood sugar regulation. 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.