Carbohydrate on long runs
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Health & Ingredients
Marathon Nutrition: How Many Carbs, Electrolytes and How Much Protein?
How many carbs to eat in marathon training, how to carb load, how much to take per hour during the race, how much to drink without risking low sodium, whether caffeine helps, and how much protein runners need.
KE
Kevin, founder of WheyWise
14 October 20269 min read
Fluid and carbs in one
Prozis
Energy IsoCarb - Isotonic Drink
800g bag
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Protein after long runs
Prozis
Supreme Whey Protein
907g bag
Buy Supreme Whey Protein →Direct from ProzisGet 10% off your order
Quick answer
For a marathon, carbohydrate is the fuel that matters. Load up with 10 to 12g of carbohydrate per kg of body weight a day for the 36 to 48 hours before the race, then take in 30 to 60g of carbohydrate an hour while you run, up to 90g an hour from a glucose and fructose mix if you will be out for more than two and a half hours. Drink to thirst rather than to a schedule: gaining weight during a marathon is the main risk factor for low blood sodium. A simple, cheap fuel to practise with is the Prozis Energy Crunch Bar, with 24g of carbohydrate in a 40g bar at 91p a bar in the 4-pack. After long runs, have 20 to 40g of protein.
Marathon nutrition comes down to three things: enough carbohydrate in training and on race day, sensible drinking with some sodium, and enough protein to recover from the training load. This guide gives the numbers the research supports, worked through for a 70kg runner, and shows which Prozis products fit around them.
How many carbs do you need in marathon training?
Marathon runners need 5 to 8g of carbohydrate per kg of body weight a day when they train for two to three hours a day, according to the British Dietetic Association. Lighter weeks of one to two hours need 3 to 5g per kg, and very heavy training of three to six hours a day needs 8 to 10g per kg.
| Training load | Carbohydrate per kg a day | For a 70kg runner |
|---|---|---|
| 1 to 2 hours, 3 to 5 times a week | 3 to 5g | 210 to 350g |
| 2 to 3 hours a day | 5 to 8g | 350 to 560g |
| 3 to 6 hours a day | 8 to 10g | 560 to 700g |
| Carb loading, last 36 to 48 hours | 10 to 12g | 700 to 840g |
Training bands from the British Dietetic Association's sport and exercise food fact sheet; carb loading from Podlogar and Wallis, 2022.
How do you carb load for a marathon?
Carb load by eating 10 to 12g of carbohydrate per kg of body weight a day for the 36 to 48 hours before the race, which is recommended for events lasting more than 90 minutes (Podlogar and Wallis, 2022, PMID 36173597). For a 70kg runner, that is 700 to 840g of carbohydrate a day. Most runners find it easier to swap some fat and fibre for low-fibre carbohydrate, such as white rice, pasta, bread, potatoes and juice, than to simply eat more.
What should you eat on race morning?
Eat a familiar high-carbohydrate, low-fat meal or snack 2 to 3 hours before the start, as the British Dietetic Association advises. Porridge, toast with honey or jam, a bagel or a banana are common choices. Race morning is not the time to try anything new: eat what you have eaten before long training runs.
How many carbs should you take during a marathon?
Take 30 to 60g of carbohydrate an hour during a marathon, and up to 90g an hour if you will be running for more than two and a half hours (Burke et al., 2011, PMID 21660838). Above about 60g an hour, use a mix of glucose and fructose: the gut absorbs the two through different routes, and the combination raised how much of the drink's carbohydrate the body burned by up to 65% compared with glucose alone (Jeukendrup, 2010, PMID 20574242).
Train your gut before race day. Runners who practised taking carbohydrate during two weeks of runs cut their stomach symptoms by about 60% and ran further in a performance test (Costa et al., 2017, PMID 28177715). Start with 30g an hour on long runs and build up.
| Finish time | Carbohydrate an hour | Total for the race |
|---|---|---|
| Under 2 hours 30 | 30 to 60g | 75 to 150g |
| 3 hours 30 | 60 to 90g, glucose and fructose | 210 to 315g |
| 4 hours 30 | 60 to 90g, glucose and fructose | 270 to 405g |
How much should you drink during a marathon?
Drink to thirst, and do not finish heavier than you started. Overdrinking is the main cause of exercise-associated hyponatraemia, dangerously low blood sodium, and the international consensus on it calls thirst-guided drinking the safest approach (Hew-Butler et al., 2015, PMID 26102445). In the 2002 Boston Marathon, 13% of 488 runners studied had low blood sodium at the finish; runners who gained weight were at about four times the risk, and those finishing in more than four hours at about seven times the risk of those under three and a half (Almond et al., 2005, PMID 15829535). At the London Marathon, 11 of 88 runners sampled had it (Kipps et al., 2011, PMID 19622524).
Sodium helps you hold on to what you drink, but it does not make overdrinking safe. Endurance athletes sweat about 1.3 litres an hour and lose about 52 mmol of sodium an hour on average, roughly 1.2g, with large differences between people (Barnes et al., 2019, PMID 31230518). A sports drink, gels with sodium or salty food cover that for most runners.
Slower runners take note: the longer you are on the course, the more chances you have to overdrink. Weigh yourself before and after a long training run: if you are heavier at the end, you drank more than you needed.
Does caffeine help in a marathon?
Yes. Caffeine at 3 to 6mg per kg of body weight, taken about 60 minutes before, improves endurance performance, according to the International Society of Sports Nutrition (Guest et al., 2021, PMID 33388079). A meta-analysis of 46 studies found time trials about 2% faster on average (Southward et al., 2018, PMID 29876876). For a 70kg runner, 3mg per kg is 210mg. Higher doses bring more side effects without more benefit, so test your dose on a long run first.
How much protein do marathon runners need?
Marathon runners need about 1.4 to 2.0g of protein per kg of body weight a day, which is the range both the International Society of Sports Nutrition and the British Dietetic Association give for endurance athletes. For a 70kg runner, that is about 98 to 140g a day. After long runs, have 20 to 40g of protein with carbohydrate, the same amount the research supports after resistance training (Jäger et al., 2017, PMID 28642676).
Protein after long runs
Prozis Supreme Whey Protein
907g bag
Prozis Supreme Whey Protein gives 24g of protein per 30g scoop, enough for the 20 to 40g runners need after a long run, at £1.22 per 25g of protein with code WHEYWISE.
or compare all UK prices →Protein after long runs
Prozis Supreme Whey Protein
907g bagPros
- + 24g of protein in a 30g scoop, inside the 20 to 40g range
- + £1.22 per 25g of protein in the 907g pouch with code WHEYWISE
- + Mixes with milk for protein, carbohydrate and fluid in one drink
Cons
- – Flavoured versions list sucralose and acesulfame K
- – Myprotein Impact Whey is cheaper per gram in its 2.5kg bag
●Nutrition per scoop · 24g protein in 30g▼
Protein makes up 80%
of this 30g scoop · 112 kcal total
24g
Protein24g
Carbs1.8g
Fat1g
Other3.2g
Which Prozis products fit marathon training?
Three Prozis products fit around marathon training: a carbohydrate bar for long runs, an isotonic drink for fluid and carbohydrate together, and whey for protein afterwards. The Prozis Energy Crunch Bar has 24g of carbohydrate in a 40g bar, so two or three bars an hour cover the 30 to 60g range on a long run. It costs 91p a bar in the 4-pack at £3.63; the 12-pack works out dearer per bar, at £1.14.
Carbohydrate on long runs
Prozis Energy Crunch Bar
The Prozis Energy Crunch Bar gives 24g of carbohydrate in a 40g bar for 91p in the 4-pack, a cheap way to practise fuelling on long runs.
The Prozis Energy Crunch Bar gives 24g of carbohydrate in a 40g bar for 91p in the 4-pack, a cheap way to practise fuelling on long runs.
Pros
- + 24g of carbohydrate in a 40g bar, so 2 to 3 bars an hour hit 30 to 60g
- + 91p a bar in the 4-pack at £3.63
- + Solid food to practise with on long training runs
Cons
- – Only 5.6g of protein a bar: it is a carbohydrate bar, not a protein bar
- – The 12-pack costs more per bar than the 4-pack
- – Chewing a bar is harder than a gel at race pace
Fluid and carbs in one
Prozis Energy IsoCarb - Isotonic Drink
800g bag
Prozis Energy Isocarb is an isotonic carbohydrate drink for long runs and race day, at £12.72 for 800g. Use it to practise fuelling and drinking together in training.
or compare all UK prices →Fluid and carbs in one
Pros
- + Isotonic carbohydrate drink powder: fluid and fuel in one bottle
- + 800g tub at £12.72, or £11.45 with code WHEYWISE
- + Four flavours, including Lemon-Lime and Orange
Cons
- – Check the label for carbohydrate per serving to plan your hourly intake
- – Drink it to thirst, not to a schedule
For more bars compared by carbohydrate, sugar and protein per bar, see the protein bar comparison.
What does a marathon fuelling plan look like?
A marathon fuelling plan for a 70kg runner aiming for about four hours puts most of the work into the two days before and the race itself.
| When | What | For a 70kg runner |
|---|---|---|
| Training weeks | 5 to 8g carbs per kg, 1.4 to 2.0g protein per kg | 350 to 560g carbs, 98 to 140g protein a day |
| Last 36 to 48 hours | 10 to 12g carbs per kg, low fibre | 700 to 840g carbs a day |
| 2 to 3 hours before | Familiar high-carb, low-fat meal | Porridge, toast, bagel or banana |
| 60 minutes before | Optional caffeine, 3 to 6mg per kg | 210 to 420mg, tested in training |
| During the race | 60 to 90g carbs an hour, drink to thirst | 240 to 360g carbs over 4 hours |
| After the race | 20 to 40g protein with carbohydrate | A whey shake with milk and a meal |
The same principles apply to recovery from any hard session; see our post-workout recovery stack for protein, creatine and rehydration in more detail.
Bottom line: carb load at 10 to 12g per kg for the last 36 to 48 hours, take 30 to 60g of carbohydrate an hour on the course, drink to thirst, and have 20 to 40g of protein after long runs. Practise all of it in training, starting with something simple like the Prozis Energy Crunch Bar at 91p a bar.
Frequently asked questions
How many carbs should you eat before a marathon?
Carb load with 10 to 12g of carbohydrate per kg of body weight a day for the 36 to 48 hours before the race. For a 70kg runner, that is 700 to 840g of carbohydrate a day. On race morning, eat a familiar high-carbohydrate, low-fat meal or snack 2 to 3 hours before the start.
How many carbs per hour during a marathon?
Aim for 30 to 60g of carbohydrate an hour. If you will run for more than two and a half hours, you can go up to 90g an hour using a mix of glucose and fructose, which the gut absorbs faster than glucose alone. Practise the amount in training first: two weeks of gut training cut stomach problems by about 60% in one study.
How much water should you drink during a marathon?
Drink to thirst. Overdrinking is the main cause of exercise-associated hyponatraemia, low blood sodium: in the 2002 Boston Marathon, 13% of 488 runners studied had it, and runners who gained weight during the race were at four times the risk. Slower runners are more exposed because they have more time to overdrink.
Do you need electrolytes for a marathon?
Sodium helps, but it does not replace sensible drinking. Endurance athletes lose about 52 mmol of sodium an hour on average in sweat, roughly 1.2g, with wide variation. Sports drinks, gels with sodium and salty food all help, but sodium cannot prevent hyponatraemia if you drink far more than you sweat.
Should you take caffeine before a marathon?
Caffeine at 3 to 6mg per kg of body weight, taken about an hour before, improves endurance performance: a meta-analysis of 46 studies found time trials about 2% faster on average. For a 70kg runner, 3mg per kg is 210mg. Test it in training, because higher doses bring more side effects and no extra benefit.
How much protein do marathon runners need?
Endurance athletes need about 1.4 to 2.0g of protein per kg of body weight a day, according to the International Society of Sports Nutrition and the British Dietetic Association. For a 70kg runner, that is about 98 to 140g a day. Have 20 to 40g after long runs.
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