How to fuel in training: pragmatic rules that actually work

You want fast running without the injury spiral or GI roulette. Fueling is not a vibe. It is logistics. Here is a clean system that scales from easy days to race day and does not implode your gut.

The big picture

• Energy availability first. If you do not eat enough, your body downshifts. Hormones, bone turnover, thyroid, mood, sleep. Performance falls even if body weight drops. If you keep getting sick, cold, irritable, or your cycle changes, you are under-fueled. Fix intake before hunting hacks.

• Fuel the work you plan to do. Higher output needs higher carbs. Long or hard needs during-session carbs. Easy or short needs less.

• Train your gut like you train your legs. Rehearse products, amounts, timing. The gut adapts. Guesswork does not.

Daily scaffolding

Breakfast on training days

• Protein 20–35 g.

• Carbs 1–2 g per kg if the key session is in the morning.

• Keep fiber modest if you run soon. If oats are your usual and you tolerate them, fine. If you always eat cornflakes before long runs, stick with that. Do not switch to “high fiber marathon porridge” the week of the race.

Between sessions

• Carbs little and often, protein 20–30 g every 3–4 hours.

• Fluids and sodium to thirst and conditions.

Evening

• Carbs to refill, protein before bed 20–30 g, fruit and veg to cover micros.

Pre, during, post: simple numbers

Before

• 3–4 hours out: 2–3 g carbs per kg, low fiber, low fat.

• 60–90 minutes out: top up with 30–60 g carbs if hungry or if the session is long.

During

• Under 60 minutes easy: fluids to thirst only.

• 60–90 minutes steady or quality: 30–45 g carbs per hour.

• 90–150 minutes or race-pace work: 60–90 g carbs per hour.

• 150 minutes plus or full marathon: 90–120 g carbs per hour if gut-trained.

Use multiple transportable carbs. Products that combine glucose and fructose help you push past 60 g per hour. Many athletes land near glucose:fructose 1:0.8 or 2:1. Tolerance is individual. Some athletes, especially during certain hormonal phases, report more GI symptoms with high fructose. Test yours in training.

After

• First 30–60 minutes: 1.0–1.2 g carbs per kg plus 20–30 g protein.

• Add sodium if you are a salty sweater or it was hot.

• Eat a real meal within 2 hours.

Product rules that save races

• Do not debut fancy gels on race week. If you have been using no-frills Decathlon gels in training and your gut is happy, keep them. Consistency beats prestige.

• Label literacy. Aim for 25–30 g carbs per gel if you are targeting 60–90 g per hour. Track fructose content across the hour, not per sachet.

• Fluids and sodium matter as much as gels. Hot marathon with no electrolytes is a cramp rehearsal. Aim for 300–800 mg sodium per liter as a baseline, more if you are very salty or it is hot. Chews or tabs are tidy on-course.

Warm up, glycogen, and context

• Marathon race day. Keep the warm up short and easy to protect muscle and liver glycogen. Walk, jog 5–10 minutes, drills, a few strides. Save fuel for 42.2.

• Training days. Warm up properly for quality. The goal is good mechanics and a primed system. You can and should still fuel. The adaptation comes from the session, not from starting it depleted.

Supplements without the fairy dust

• Caffeine. Useful for performance at 1–3 mg per kg total dose, split between pre start and mid race. In the heat, start lower. Caffeine itself is not a major dehydrator during exercise but it can upset your gut and crank your perceived effort. Test carefully.

• Sodium bicarbonate. Best for middle distance and short high-intensity work. Not a marathon tool for most runners. GI risk is high. If you ever use it, only in rehearsed, shorter events or sessions.

• Ketones. Not a primary fuel for marathons. Evidence is mixed. If you experiment, do it far from key races.

• Tart cherry. Good for recovery after a race or occasional breakthrough sessions. Do not sip it during training blocks expecting magic. Regular use around every session may blunt some training adaptations. Save it for true recovery windows.

Race-day fueling plan you can actually follow

48–24 hours out

• Raise carbs across meals. Think rice, pasta, potatoes, bread. Keep fiber sensible. Salt food to taste. Drink to thirst.

Race morning

• 3 hours out: breakfast with 2–3 g carbs per kg, low fiber, low fat, 20–25 g protein.

• 30–15 minutes out: one gel or 20–30 g carbs. Small sip of water.

During the marathon

• Aim for 90 g carbs per hour if you have trained for it. If not, target 60 g and build next cycle.

• Example schedule at 90 g per hour: one 30 g gel every 20 minutes, plus small water sips. If using bottles, mix to hit the hourly target. Add electrolytes according to heat and sweat rate.

Finish

• 1.0–1.2 g carbs per kg plus 20–30 g protein in the first hour. Real meal within 2 hours. If you like tart cherry, this is the moment.

Hot weather playbook

• Start slightly conservatively on caffeine.

• Front-load sodium across breakfast and bottles.

• Increase fluid access. Do not chug at one station, sip often.

• Use cooling: ice, sponges, shade when available.

Common mistakes that ruin stomachs

• New gels on race week.

• Oats if you never eat oats. If your pre-run habit is cereal and a banana, stay with it.

• Chasing bicarb for a marathon.

• Forgetting sodium and only taking sweet gels in heat.

• Overstuffing the first 20 minutes, then going dry for 40 minutes. Even spacing is kinder to the gut.

Signs you are not eating enough

• Performance stalls even as body weight drops.

• Poor sleep, low mood, frequent illnesses.

• For women, cycle changes. For men, lowered libido and morning energy.

• Bone or tendon niggles that will not quit.

If two or more of these hit at once, add calories, especially carbs around training, and review weekly load.

Practice timeline and cost reality

• Time needed to lock your plan. Give yourself 6 to 10 long runs and 4 to 6 quality sessions to train the gut and settle on product mix, volumes, and timing.

• Typical cost per long run. Two to four gels and a bottle setup costs about €5 to €12 depending on brand. A marathon itself usually runs €15 to €35 in fueling if you target 90 g per hour.

Quick menus that work

Pre long run, 3 hours out

• Bagel with honey, yogurt, banana.
  500 ml water with electrolytes.

During long run at 90 g per hour

• Gel at 20, 40, 60, 80 minutes.

• 500–750 ml per hour total fluids. Add sodium by heat.

Post

• Large rice bowl with eggs or chicken and veg.

• Yogurt with fruit later.

Pre track session, 90 minutes out

• Cereal with milk and a banana, or white toast with jam.

• One small gel on the start line if you like a kick.

Female specific notes worth testing

• Some runners report more GI sensitivity at certain times of the cycle. This is normal. If so, slide toward the lower end of fructose intake, keep fiber low the evening before, and split gels into smaller, more frequent doses. Test and log.

What to remember

Fuel enough every day. Rehearse your race plan. Keep products consistent. Respect sodium in the heat. Save the exotic supplements for the right events. If your body is sending low-energy signals, fix intake before chasing marginal gains.

Photos

Photo by Kouji Tsuru