How Many Carbs Do I Need Before a Long Run?
For a run that will last about an hour or more, plan 1–4 grams of carbohydrate per kilogram of body weight in the 1–4 hours before you start. That is the pre-event fuelling line in the Academy / Dietitians of Canada / ACSM nutrition and athletic performance position paper. At 70 kg, that is 70–280 grams. The wide range exists because a 70 g breakfast two hours out is a different meal from 200 g of pasta four hours out.
Easy 30-minute jogs do not need this protocol. Long runs, race-pace sessions, and anything that empties glycogen do. This is educational coaching for typical trainees, not medical advice. Tomorrow’s scale may rise after a high-carb breakfast and a bottle; that is glycogen and water, not a weekend of fat.
When the 1–4 g/kg rule applies
Muscle and liver glycogen are limited. The ACSM-linked table pairs the pre-event dose with time: more hours of digestion allow a larger meal; less time means a smaller, lower-fiber plate. High fat, huge protein, and a lot of fiber in that meal raise the chance of GI trouble.
Daily carbohydrate still sits on top of this. The same paper scales daily carbs to training load — roughly 3–5 g/kg on light days up through 8–12 g/kg for very high volumes. A long-run Saturday is a high-availability day even if Thursday was not. ISSN’s nutrient-timing stand agrees that extended high-intensity work challenges fuel supply.
Skip the full protocol when:
- The run is an easy 20–40 minutes and you ate a normal meal in the last few hours
- You are walking, not running, and the outing is short
- You are doing a brief shakeout the day after a long run
Use the protocol when:
- You will be out about 60 minutes or more at a real running effort
- The session includes long intervals or race pace
- You have a history of fading in the last third of the long run on water alone
Early-morning long runs collide with what to eat before a morning workout. The long-run rule still applies; the portions shrink toward the low end of the range because you do not have four hours.
Key takeaway: The 1–4 g/kg range is for long or hard running, matched to the hours you have — not for every easy jog.
Match the grams to the clock
| Time before start | Toward which end of 1–4 g/kg | Texture |
|---|---|---|
| 3–4 hours | Middle to high | Cooked grains, rice, potatoes, pancakes, a little yogurt |
| 2 hours | Middle | Oats, bread, banana, jam |
| 45–75 minutes | Low | White toast, ripe banana, sports drink, applesauce |
| Under 30 minutes | Only if you know your gut | Gels or a few sips of drink — this is not a full 4 g/kg sitting |
At 70 kg:
- 1 g/kg = 70 g carbohydrate
- 2 g/kg = 140 g
- 4 g/kg = 280 g — a large meal that needs hours, not a parking-lot bite
140 g of carbohydrate is 560 kcal before you add fat or protein. That is why daily calorie targets still matter over the week. One long-run breakfast does not erase a 3,000 kcal Saturday. Hall and colleagues (2012) treat energy as a budget with several parts; the run is one part. Mifflin-St Jeor still sets the resting piece of the day.
Protein can sit in the meal in a small amount. ISSN’s 20–40 g serving is useful across the day. A large protein feeding right before a long run is slow and not the fuel the performance paper is targeting. Save the 35 g yogurt bowl for after you finish, or keep it small if it already sits well.
Fiber belongs in the week. Move the high-fiber meals away from the start line — beans and a big salad at dinner the night before, or at lunch after you finish — not in the hour you pin on a bib.
Key takeaway: More hours allow more grams. Forty minutes before the start is a 1 g/kg snack, not a 4 g/kg platter.
Worked example: 70 kg, 18 km Sunday
Goal: start comfortable, not stuffed, not empty.
Option A — 3 hours before, 2 g/kg = 140 g carbohydrate
A plate in the neighborhood of typical grocery labels:
- 100 g dry oats cooked in water (~66 g carbs) plus a tablespoon of honey (~17 g)
- 2 slices sandwich bread (~28 g)
- 1 large banana (~27 g)
- 250 ml orange juice (~26 g)
That is about 160 g if you finish the juice — close enough. Keep butter light. Drink fluid with it; see water when you exercise.
Option B — 60–90 minutes before, 1 g/kg = 70 g
- 1 large bagel (~50–60 g depending on size) or 3 medjool dates plus a banana
- Water or a weak sports drink
During the run if you will be out 90+ minutes: 30–60 g/hour from drink mix, chews, or food you have already tested. ISSN discusses that hourly band for extended high-intensity work. ACSM lists up to about 90 g/hour for ultra-endurance with mixed glucose/fructose sources. Do not debut that on race day.
After: a normal meal with carbs and protein. You do not need a separate “loading dinner” unless next week is a long event and your daily intake was low. Eating after a strength workout is a different job; after a long run you still want protein, but carbohydrate refill is more of the story.
| Piece | Before (fasted 18 km, water only) | After (option B + during-run carbs) |
|---|---|---|
| Carbohydrate before the start | 0 g | ~70 g |
| Carbohydrate during 90+ minutes | 0 g | ~40 g/hour |
| Breakfast calories | 0, then a huge unplanned brunch | ~300–350 planned, then a normal lunch |
The “after” column is still food you log. Put the breakfast in MyFitnessPal or Cronometer the night before if mornings are chaotic. Garmin can store the run; it should not invent a second breakfast you then eat on top of a full day.
Key takeaway: At 70 kg, 70 g about an hour out plus practiced hourly fuel beats a fasted fade and a revenge brunch.
Daily carbs, calories, and the rest of the week
Pre-event food cannot refill what five low-carb days emptied. If weekday intake sits at 50 g of carbohydrate because a trend said so, one bagel will not fix Sunday. Set a daily carbohydrate band with the carbohydrate calculator using your usual calorie target and an endurance-leaning split on long-run days.
Confirm the day’s energy in the calorie calculator so the 560 kcal breakfast is planned. If you are in a fat-loss phase, you still fuel the long run; you trim later meals or extras, not the practiced start-line food. If you skip the bagel to “save” calories and then buy pastries at kilometer 12 of the day, the week did not get cleaner.
Rest days after a long run still need food. Glycogen refill continues. See calories on rest days before you crash Thursday because the long run is “done.”
People with diabetes or clinician-set carbohydrate limits should not copy race-week plates from a website. That is a clinic conversation.
This is a good point to stop guessing the plate. Ask what should I eat for a 70 g or 140 g carb meal that uses food you already buy. Then write one sentence on your phone: time before run, grams of carb, what you ate, how the gut felt at kilometer 10. That log is worth more than another generic plate photo.
Key takeaway: Daily carbohydrate and the day’s calorie budget carry the long run. The pre-run plate is a deposit, not a full refill of a depleted week.
Train the gut on purpose
GI comfort is specific. Heat, nerves, and a new course change it. Repeat the same breakfast on two training weekends before you trust it on race morning.
What to practice:
- The exact bagel size, not “a bagel”
- The drink mix concentration you will use
- Whether milk in the oats is acceptable for you
- The timing: 75 minutes versus 3 hours
What not to copy from social media:
- Carb loading for a 5K
- Fasted 30 km “to burn fat” as a weekly habit if the goal is a better long run
- A fiber-rich bean burrito 40 minutes before a tempo
- A new sugar-alcohol gel
- Daily carbs at 50 g all week, then surprise that 15 km feels empty
If a humid disaster happens once, do not throw out the plan. Repeat the same breakfast on a cooler weekend. If the same breakfast fails twice, shrink the portion or move it earlier — do not add a third new product.
Key takeaway: Practice the meal and the hourly fuel on training weekends. Race morning is the wrong time to meet a new gel.
Common mistakes
Eating 4 g/kg 40 minutes before the run. That is a 280 g carbohydrate bomb at 70 kg — a huge meal in the wrong time slot.
Skipping daily carbs all week, then eating one pre-run plate. Pre-event food is a deposit, not a resurrection.
Using protein powder as the pre-run meal. Protein is slow here.
Drinking only water for a 2.5-hour effort. Fluid and carbohydrate can travel in the same bottle.
Judging a fueling plan by one humid disaster. Heat and nerves change GI comfort.
Treating the long-run breakfast as free, then eating a full unlogged day. Mifflin-St Jeor plus activity still describes the week.
Carb-loading for a 10K you can finish on daily meals. Classic loading is for longer events.
Reading the morning-after weigh-in as fat gain. Glycogen holds water. Hall’s energy-balance picture is slower than one Sunday scale bounce.
Key takeaway: Wrong portion, wrong clock, and unlogged brunch cause more problems than a missing branded gel.
What to do next
- Set a daily carbohydrate band with the carbohydrate calculator using your usual calorie target and an endurance-leaning split on long-run days.
- Confirm the day’s energy budget in the calorie calculator so the 560 kcal breakfast is planned, not accidental.
- Ask what should I eat for a 70 g or 140 g carb meal that uses food you already buy.
Write the one-line log after the next long run. Adjust grams or timing once. Then leave the plan alone for two weekends so you can tell whether the gut, not the weather, was the problem.
Key takeaway: Size the pre-run meal in grams you can repeat. Change one variable after two weekends, not every Saturday.