How Many Carbs Do You Actually Need Per Hour of Exercise?

Photo: SportPlus.sg / Isis Ang

The Absorption Bottleneck: Why "Multiple Transportable Carbs" Matter

To understand why you cannot simply swallow five glucose gels an hour, you have to look at the lining of your small intestine.

• The SGLT1 Bottleneck: Glucose and maltodextrin rely on a specific intestinal transport protein called SGLT1 to move from your digestive tract into your bloodstream. SGLT1 transporters max out at approximately 60 grams per hour. If you ingest 80 grams of pure glucose in an hour, the extra 20 grams sit unabsorbed in your gut, drawing in water and triggering bloating, nausea, or runner’s trots.

• The GLUT5 Bypass: Fructose does not use SGLT1. It enters the bloodstream through an entirely separate intestinal doorway called GLUT5. By combining glucose/maltodextrin with fructose in scientifically backed ratios (such as 2:1 or 1:0.8), you bypass the SGLT1 bottleneck. This unlocks systemic carbohydrate oxidation rates of 90 grams per hour or more.

When selecting endurance nutrition for hard or long efforts, examine the ingredient deck. Formulations that balance multiple carbohydrate types allow your body to process high energy volumes without stomach distress.

How to Match Your Intake to Your Training Session

1. Mid-Week Easy & Recovery Runs (< 75 Mins)

Your resting liver and muscle glycogen stores comfortably supply roughly 90 minutes of steady aerobic running. Outside of sipping plain water or light electrolytes in high heat, you do not need exogenous carbohydrates for shorter sessions.

2. Half Marathon Workouts & Steady Long Runs (1.5 to 2.5 Hours)

Aim for 30g to 60g of carbohydrates per hour. This preserves stored glycogen so your legs feel strong through the final kilometres and speeds up your post-run muscular recovery. A simple routine of one quality gel every 30 to 40 minutes hits this zone cleanly.

3. Full Marathons & Peak Long Runs (2.5 to 4+ Hours)

Target 60g to 90g per hour. Because liver glycogen empties predictably past the two-hour mark, staying above 60g/hr is the single most reliable safeguard against hitting the wall.

Photo: SportPlus.sg / Isis Ang

Building Tolerance: Do Not Jump Straight to 90 Grams

Absorbing 60 to 90 grams of carbohydrates per hour while bouncing along pavement requires deliberate digestive conditioning.

• Progress in 15g Increments: If you currently take one 25g gel every 45 minutes (~33g/hr), do not jump straight to 80g/hr next weekend. Step up to 45g/hr for two weeks, evaluate how your stomach handles the volume, and then graduate toward 60g/hr.

• Always Pair with Plain Water: High-carb intake requires sufficient water volume (roughly 100ml to 150ml per 20–25g of carbs) to balance gut osmolality and promote smooth gastric emptying.

Dial Your Hourly Targets with ATHLO+

Hitting precise hourly carbohydrate targets is much easier when you use fuel engineered specifically for clean absorption and high bioavailability.

• Engineered for Endurance: Discover ANS Nutrition gels on ATHLO+—formulated with clean, easily digestible carbohydrate profiles designed to deliver reliable energy without upsetting your stomach.

• Streamline Your Training: Build out your training packs, hydration flasks, and race-day fuel kits seamlessly in one place.

Ready to train your stomach to handle higher carbohydrate volumes comfortably? Read our comprehensive guide on runner's gut training next.