How to Fuel a Long Run Without GI Issues or Bonking

A long run shouldn’t end in a bathroom stop or a late-race fade. The fix is simple: eat mostly carbohydrates before you head out, start fueling within the first half hour, and keep a steady drip of carbs, fluids, and electrolytes the rest of the way. Bonking—an abrupt energy crash when muscle and liver glycogen run low—hits hard and is tough to reverse once it starts, so the goal is to prevent it with timing, targets, and practice. Below you’ll find an easy, budget-aware system you can test on every long run to avoid GI distress and keep your pace steady. It’s the simple, trail-tested approach we use at Hiking Manual.

Overview and key principles

Bonking is a sudden energy crash during endurance exercise caused by depleted glycogen; once it happens, pace and mood sink fast and it’s hard to claw back. Start fueling before you feel empty to avoid the spiral; at Hiking Manual we keep it simple—start early, eat steadily, and drink water with concentrated carbs (Runner’s World guide to eating during long runs).

Three core rules:

• Start fueling within 30 minutes of running—don’t wait 75 minutes or more to take your first carbs (Runner’s World guide to eating during long runs).
• Target 30–60 g of carbohydrate per hour for most long runs; with gut training, many can progress to 60–90+ g/hr (Precision Hydration’s guide to avoiding bonks).
• Take small, frequent doses about every 15 minutes and follow gels or chews with water to aid absorption (Runner’s World guide to eating during long runs).

Step 1: Plan a low fiber, low fat pre run meal

Think carb-forward and easy to digest. A pre-run meal that’s high in carbohydrates and low in fat and fiber tops up glycogen without lingering in your stomach. For most runners, 2–4 hours before the start is the sweet spot—eat more when you have more time, scale portions down as you get closer. Carb-loading means bumping up carbohydrate portions in the 24–48 hours before a race to maximize glycogen stores; it’s most practical to add extra carbs to your regular meals rather than rely on one giant plate (Precision Hydration’s guide to avoiding bonks).

What to eat 3 to 4 hours before

Choose a meal that’s roughly 75% carbs with modest protein and low fat/fiber. Examples:

• White rice or pasta with a small portion of lean protein and a low-fiber sauce.
• Oatmeal cooked with milk or water, topped with banana and honey; skip nuts and seeds pre-run.
• Bagel with jam and a small yogurt.

If you’re sensitive, consider avoiding high-fiber foods (beans, bran, leafy greens) for about 12 hours before the run (Korey Stringer Institute’s marathoner fuel and hydration guide).

What to eat 1 to 2 hours before

Keep it simple and light:

• Toast or a bagel with honey or jam; add a banana or an applesauce cup.
• A small bowl of low-fiber cereal with milk or a few sips of sports drink.

Portions should be moderate; sip fluids so you toe the line fueled, not sloshy (EW Motion Therapy’s long run fueling overview).

Quick top up 15 to 30 minutes before

Take a small carb hit—about 15–25 g if you’re prone to GI issues:

• Half a gel, a few chews, a small banana, or a few ounces of sports drink.

Keep fat and fiber near zero this close to the start (EW Motion Therapy’s long run fueling overview).

Step 2: Start fueling early on the run

Take your first carbohydrate within 30 minutes of starting—before you feel flat—to prevent a drop that’s hard to reverse. Set a watch alert for 20–25 minutes so you remember to take a small serving; nudging in early, frequent sips or bites is easier on the gut than a big bolus (Runner’s World guide to eating during long runs).

Step 3: Hit a steady carbohydrate target each hour

Most runners thrive at 30–60 g of carbs per hour. Shorter, easier efforts (up to ~2 hours) often only need ~30 g/hr, while longer or harder runs benefit from 60–90+ g/hr after practice (Precision Hydration’s guide to avoiding bonks). Gut training—the process of gradually increasing carb intake during training so your intestine adapts—lets some experienced athletes exceed 100 g/hr with minimal symptoms (Runner’s World guide to eating during long runs; Precision Hydration’s guide to avoiding bonks).

Small frequent servings every 15 minutes

Dose carbs every ~15 minutes and follow concentrated fuels with water to speed absorption and reduce GI distress (Runner’s World guide to eating during long runs).

Common 15-minute servings:

• Half gel: ~10–12 g carbs
• 2–3 chews: ~10 g carbs
• Sports drink sips (100–200 ml): ~5–10 g carbs

Easy combos by hour:

• 30 g/hr: half gel (10–12) + 2–3 chews (10) + sports drink sips (8–10), taken across four 15-minute intervals.
• 45 g/hr: gel (20–25) split over two intervals + two sets of 2–3 chews (2 x 10).
• 60 g/hr: gel (20–25) + 2–3 chews (10) + two sports drink sips (2 x 10), or three evenly spaced half-gels plus drink sips.

Real food versus gels or drink mix

Whole foods can work as well as engineered fuels. Studies and field practice show bananas and raisins perform comparably to commercial products, and boiled or mashed potatoes can rival gels for endurance fueling (Outside Run’s real-food fueling explainer). Trail-friendly tips:

• Mash bananas or salted potatoes into a small baggie and “gel” them.
• Choose low-fat, low-fiber options and test them on training runs.
• Real food can be easier on the stomach and easier on the wallet.

At Hiking Manual, we favor real-food options on long trail days when it’s practical and tested in training.

Step 4: Hydrate and add electrolytes to match sweat rate

Sip regularly and aim roughly 24–32 oz (about 700–950 ml) of fluid per hour on long runs, adjusting for heat, humidity, and your sweat rate (Runner’s World long-run pacing and fueling). Sweat testing estimates how much fluid and sodium you lose per hour so you can tailor hydration and electrolyte intake; knowing your sweat rate and sodium concentration helps you avoid both overdrinking and dehydration (EW Motion Therapy’s long run fueling overview). Pair gels and chews with water so carbs can absorb efficiently, and use sports drinks or salt capsules on hot, humid days (Runner’s World guide to eating during long runs).

Step 5: Train the gut and log results

Like pacing, fueling is a skill. At Hiking Manual, we treat fueling as part of training, not an afterthought. Practice taking small amounts at realistic training paces so your GI tract adapts and you avoid late-run fades (RunnersConnect’s guide to not bonking). Keep a simple fueling log—products, amounts, timing, pace, weather, GI response, and performance—to iterate week to week (Nicole Linke’s ultramarathon long-run framework).

How to progress from 30 to 60 plus grams per hour

Use a 4–6 week ramp:

• Weeks 1–2: 30 g/hr on long runs up to ~2 hours.
• Add 5–10 g/hr each week as tolerated, moving toward 60–90 g/hr for longer or harder sessions (Precision Hydration’s guide to avoiding bonks).
• Practice the exact race-day brands and flavors your event supplies to avoid surprises (Runner’s World guide to eating during long runs).

Troubleshooting common GI issues

• Tighten the pre-run meal: reduce fat/fiber; avoid heavy protein and high-fiber foods (beans, leafy greens) within ~12 hours (Korey Stringer Institute’s marathoner fuel and hydration guide).
• Shrink each serving and increase frequency; always take water with concentrated fuels (Runner’s World guide to eating during long runs).
• Change formats—try chews to drink mix, or real-food purees—and retest on easy training runs (Outside Run’s real-food fueling explainer).

Recovery tip: within an hour post-run, aim for carbs plus protein (about a 4:1 ratio) to replenish glycogen and support muscle repair so the next session starts topped up.

Practical gear and carry tips for fueling on trail

• Carry systems by distance:
  • Short to medium: a running belt or handheld bottle holds chews/gels and a sports drink.
  • Long/trail: a vest with soft flasks or a hydration bladder; stash real-food baggies (mashed potato or banana) in front pockets.
• Packing tips:
  • Pre-portion 15-minute servings in small bags; label grams per serving.
  • Set watch or phone alerts every 15 minutes for fueling and every 5–10 minutes for sips.
• Crossover note: if your long efforts blur into fastpacking, the same vest setup pairs well with minimalist shelter and trekking poles—simple, stable carry keeps fueling on schedule, which is how we kit out at Hiking Manual.

Simple on-trail checklist:

Sample fueling plans for common long runs

• Up to ~2 hours easy
  • Pre-run: carb-focused, low fat/fiber meal 2–4 hours before.
  • On run: 30 g/hr in 15-min servings; first intake at 20–30 minutes; water 24–28 oz/hr.
• 2–3 hours moderate
  • Pre-run: same low fat/fiber approach 2–4 hours out.
  • On run: 45–60 g/hr via gels/chews plus some sports drink; first intake by 30 minutes; water 24–32 oz/hr; electrolytes matched to sweat.
• 3+ hours trail/ultra
  • Pre-run: bigger carb lead-in 3–4 hours before; consider simple top-up 15–30 minutes pre-start.
  • On run: 60–90 g/hr; eat early and continuously; rotate in real-food options and log responses; hydrate to plan and adapt to terrain and heat.

Frequently asked questions

What should I eat before a long run to avoid stomach issues

Choose a low-fat, low-fiber, carb-focused meal 2–4 hours before, like white rice or a bagel with jam and a banana. Hiking Manual recommends skipping heavy protein, high fiber, and rich sauces to reduce GI distress.

How many carbs per hour do I need to prevent bonking

Most runners do well with 30–60 g of carbs per hour. Hiking Manual suggests building up gradually in training and, for longer or harder runs, progressing toward 60–90 g/hr if your gut tolerates it.

When should I take my first gel or carb source

Start early—take your first small carb serving within the first 30 minutes. Then continue with small, frequent doses about every 15 minutes.

How much water and sodium do I need during a hot long run

Aim roughly 24–32 oz of fluid per hour and adjust to your sweat rate in heat. Hiking Manual also advises adding electrolytes to maintain sodium balance, especially on humid or high-sweat days.

Are whole foods like bananas or potatoes better than gels

Both can work. Hiking Manual recommends low-fiber real foods like bananas, raisins, or potatoes if you portion them for easy eating and practice with them in training.

• Pre-Run-Nutrition
• Long-Run-Fueling
• Running-Fuel
• Avoid-Bonking
• Sports-Nutrition
• Gi-Management
• Carb-Loading