Cutting out added sugars is a widely praised dietary change for long-term health — but for athletes and active individuals, the transition requires careful attention to overall carbohydrate intake and calorie balance. Here is what the evidence and practical experience suggest for anyone navigating this change while maintaining physical performance.
Why Performance May Drop After Cutting Added Sugar
The most common reason performance declines after removing added sugar is not the absence of sugar itself, but the resulting drop in total carbohydrate and calorie intake. Pastries, chocolate, and similar foods — while nutritionally poor — do contribute meaningfully to daily energy intake. If those calories are not replaced with other fuel sources, the body can find itself under-fueled during training.
For explosive, high-intensity activities like bouldering, the body draws heavily on stored muscle glycogen (carbohydrate reserves). If glycogen stores are consistently depleted and not replenished, performance in power-dependent movements will suffer. This is not a consequence of avoiding sugar — it is a consequence of consuming insufficient carbohydrates overall.
What to Replace Added Sugar With
The goal is not to find a "healthier sugar" as a direct substitute, but to ensure total carbohydrate and calorie targets are still being met through nutrient-dense sources. The following are practical options:
- Whole fruits — provide natural sugars, fiber, and micronutrients. Particularly useful as a pre-session energy source.
- Oats and whole grains — slower-digesting carbohydrates that support sustained energy levels throughout the day.
- Sweet potatoes and potatoes — calorie-dense, rich in complex carbohydrates, and easy to integrate into meals.
- Brown rice and legumes — solid staples for meeting carbohydrate needs without added sugar.
Timing also matters. Consuming a moderate amount of carbohydrates 60–90 minutes before a climbing session can help ensure glycogen stores are topped off before explosive effort begins.
Does Bouldering Actually Require Carbohydrates?
Yes — though the mechanism is different from endurance sports. Bouldering sessions are typically intermittent: short, maximal-effort climbs interspersed with rest periods. This structure means the body relies primarily on the phosphocreatine and glycolytic energy systems rather than sustained aerobic metabolism.
Research on sport climbing nutrition, including a review published in the journal Nutrients, notes that climbing training often exceeds 60 minutes in total duration, but the actual time spent under physical load is much shorter and interval-based. Sports drinks containing carbohydrates are therefore not particularly useful for bouldering — but maintaining adequate daily carbohydrate intake absolutely is.
The same research highlights several supplements that may benefit climbers: beta-alanine, caffeine, nitrates, and sodium bicarbonate have shown some evidence of performance support in climbing contexts. Creatine is also discussed, though potential side effects such as water retention may be a consideration for weight-sensitive climbing disciplines.
Source: PMC — Nutritional Strategies and Supplements for Climbers (Nutrients, 2023)
Protein Intake for Intermittent Sports
Climbing is an intermittent-intensity activity with a meaningful strength component, particularly in the upper body and core. Based on research on protein requirements for intermittent sports (including a widely cited review published in the Journal of the International Society of Sports Nutrition), a daily protein target of approximately 1.4–1.7 g per kilogram of body weight is a reasonable range for athletes in this category.
A practical middle-ground target of 1.6 g/kg is commonly cited for active individuals engaged in mixed-intensity training. Whether protein supplements are necessary depends entirely on whether this target can be reached through whole foods alone — many active people can meet it without supplementation.
Source: PMC — Protein Requirements for Athletes: A Review (JISSN)
Tracking Intake During the Transition
One of the most effective ways to diagnose a performance drop during a dietary transition is to temporarily track macronutrient and calorie intake. Many people discover that cutting out processed foods — even unhealthy ones — results in a significant unintentional calorie deficit. Tracking for two to four weeks can reveal whether total energy, carbohydrate, or protein intake has fallen short of what the body needs to sustain training.
Summary
Cutting added sugar is a sound health decision. However, the performance drop that sometimes follows is usually not caused by the absence of sugar — it is caused by failing to replace the energy that sugar was providing. For a physically active person with a high daily energy demand, this gap can become significant over several weeks. Replacing added sugar with quality carbohydrate sources, monitoring total calorie intake, and paying attention to pre-session nutrition are the most straightforward steps toward recovering and potentially improving performance.
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