Carbohydrates: Friends or Foes?

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Few foods get as much bad press as carbohydrates. Social media often portrays them as the enemy to be avoided if you want to lose weight. The reality is more nuanced: carbohydrates are the body’s main source of energy—and it all depends on the type, the amount, and the timing of when you eat them.

Simple or Complex: The Real Distinction

Simple carbohydrates (sugars) are digested quickly: they cause a sudden spike in blood sugar levels, followed by an equally rapid drop that leads to hunger and fatigue. They are found mainly in added sugars, sugary drinks, and refined foods.

Complex carbohydrates—whole grains, legumes, fruits, and vegetables—release their energy gradually, providing long-lasting satiety. Among these, fiber stands out: since it is not digested, it nourishes the gut microbiota and supports digestive health.

The Fuel for Effort

During exercise, the proportion of carbohydrates depends on the intensity. At low to moderate intensity (about 50 to 75% of VO₂max), fat remains the primary fuel source, and carbohydrates account for 30 to 40%. Above 70% of VO₂max, carbohydrates become the dominant fuel source—accounting for up to 70% of the energy expended. The more intense the effort, the more your body relies on carbohydrates.

That's exactly the logic behind your training zones.

Proper Nutrition Around Your Workout

Glycogen stores are limited. For endurance exercise lasting more than 60 minutes, a meal rich in complex carbohydrates 2 to 3 hours beforehand helps prevent hypoglycemia. After exercise, a combination of carbohydrates and protein (approximately 1 to 1.2 g/kg of carbohydrates per hour during the first few hours, along with protein) optimizes recovery and glycogen resynthesis.

When Carbs Are Harmful

The problem isn't carbohydrates themselves, but an excess of simple carbohydrates. A high intake of fast-acting sugars causes a sharp spike in insulin; over time, this hyperinsulinemia promotes insulin resistance, the accumulation of visceral fat, obesity, and type 2 diabetes.

Fiber: A Partner in Good Health

Conversely, dietary fiber has protective effects. Soluble fiber (beta-glucans, pectins, inulin) lowers cholesterol, regulates blood sugar levels, and nourishes gut microbiota that produce anti-inflammatory compounds. Insoluble fiber promotes regular bowel movements and a feeling of fullness. The goal: 25 to 30 g of fiber per day, and at least 130 g of carbohydrates daily just to ensure proper brain function.

References

Clemente-Suárez VJ et al. “The Burden of Carbohydrates in Health and Disease.” Nutrients. 2022;14(18):3809.

Jeukendrup, A. “A Step Toward Personalized Sports Nutrition: Carbohydrate Intake During Exercise.” Sports Med. 2014;44(Suppl. 1):S25–33.

Alghannam AF, Gonzalez JT, Betts JA. “Restoration of Muscle Glycogen and Functional Capacity: Role of Post-Exercise Carbohydrate and Protein Co-Ingestion.” Nutrients. 2018;10(2):253.

Soliman GA. “Dietary Fiber, Atherosclerosis, and Cardiovascular Disease.” Nutrients. 2019;11(5):1155.

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This article is provided for educational purposes only and does not constitute medical advice. If you have any health conditions, consult a doctor before starting to exercise.