Running Nutrition Guide: What Your Body Really Needs Between Races

You've memorised your gel strategy. You know exactly when to take the first one, how many you'll carry, and which flavour doesn't make you gag at mile 18. You've read the carb-loading guides. You've got your pre-race breakfast dialled in. Race-day nutrition? Sorted.

But here's the thing most runners don't want to hear: what you eat on race day is almost irrelevant compared to what you eat in the weeks and months beforehand. The energy gels and isotonic drinks you rely on during a marathon are just short-term fuel for an engine that's already been built — or not built — by your daily nutrition. And for most runners, that daily foundation is full of gaps they don't even know exist.

This guide is about filling those gaps. We'll cover why runners have genuinely different nutritional needs to the average person, the five key things that high-mileage training depletes (and what to do about each one), how your nutritional priorities should shift across your training year, and how to build a practical daily nutrition plan that supports everything from your Tuesday track session to your Sunday long run. Whether you're training for your first Parkrun 5K or your third London Marathon, this is the nutrition guide you actually need.

Why Runners Have Different Nutritional Needs

The NHS Eatwell Guide is a reasonable starting point for a sedentary adult — but it wasn't designed with a runner doing 40 miles a week in mind. The physiological demands of regular endurance running create nutritional requirements that go well beyond what a standard healthy diet can reliably address.

The most obvious difference is energy. A runner covering 40 miles a week might burn an additional 3,000–4,000 calories above their basal metabolic rate from running alone. That's a lot of food to eat — and a lot of micronutrients that need to come with it. But energy is only part of the story.

High-mileage running generates mechanical stress, oxidative stress, and systemic inflammation at a level the human body simply wasn't designed to sustain week after week. Every foot strike sends a shockwave through your skeleton. Your muscles are repeatedly damaged and repaired. Your immune system is chronically stimulated. Your cardiovascular system is under prolonged demand. Each of these processes has nutritional dependencies — and when those nutrients are in short supply, recovery slows, performance suffers, and injury risk rises.

There's also the matter of loss. Runners lose significant quantities of iron, sodium, magnesium, zinc, and other minerals through sweat — and through a mechanism specific to running called foot-strike haemolysis, where the repeated impact of the foot on the ground literally destroys red blood cells.^[1] These losses need to be replaced, and a standard diet rarely compensates for them automatically.

Add to this the fact that the UK's climate makes vitamin D deficiency almost a certainty for most of the running year — the sun simply isn't strong enough between October and April to trigger adequate synthesis^[2] — and you start to see why the nutritional picture for UK runners is more complicated than just eating well and having a banana before your long run.

For a full breakdown of how RunStrong's formulation addresses these needs, see our complete guide to RunStrong's daily supplement for runners.

The Five Things High-Mileage Running Depletes

Rather than listing every nutrient a runner might need, it's more useful to focus on the ones where the gap between what running demands and what a typical diet provides is largest. These are the five areas where runners are most consistently under-supported — and where targeted nutrition makes the biggest difference.

1. Iron — The Performance Thief You Don't See Coming

Iron deficiency is the single most common nutritional problem in distance runners, and it's particularly prevalent among female runners — research suggests up to 50% of female endurance athletes have suboptimal iron status.^[3] But male runners aren't immune, especially those running high mileage on hard surfaces.

The reasons are multiple and compounding. First, there's foot-strike haemolysis — the mechanical destruction of red blood cells caused by the repeated impact of your foot on the ground. Every step you take ruptures a small number of erythrocytes, releasing haemoglobin into the bloodstream that the kidneys then excrete. Studies have confirmed that this effect is real and significant, particularly on hard surfaces.^[1] Second, runners lose iron through sweat — more than most people realise. Third, the inflammatory response triggered by endurance training elevates a protein called hepcidin, which actively suppresses iron absorption in the gut for several hours after exercise. You can read more about this mechanism in our deep-dive on why runners are at risk of low iron levels.

The consequences of iron depletion aren't subtle once they take hold: persistent fatigue, elevated heart rate, declining performance, and the inability to hit paces that used to feel easy. Many runners spend months wondering why their fitness has plateaued before anyone thinks to check their iron levels. If this sounds familiar, our article on runner's anaemia — the hidden performance thief is worth a read.

What makes this tricky is that not all iron is created equal. Iron bisglycinate — the form used in RunStrong — has approximately 90% bioavailability compared to the iron sulphate typically found in standard supplements, and it's far gentler on the gut. The haem iron in red meat is also well absorbed, which is why female runners following plant-based diets are at particularly high risk and need to be especially proactive.

2. Anti-Inflammatory Capacity — Why Your Body Can't Keep Up

Every run you complete creates a controlled degree of muscle damage and inflammation. That's not a bug — it's the signal that drives adaptation. But when you're training consistently, week after week, the acute inflammation from each session can start to compound into chronic low-grade inflammation throughout the body. This manifests as persistent soreness, slower recovery between sessions, and an increased susceptibility to minor soft tissue injuries.

The body has its own antioxidant and anti-inflammatory systems, but in high-mileage runners these systems are frequently overwhelmed. Dietary antioxidants from fruit and vegetables help — but even a good diet often isn't enough to keep pace with the inflammatory load of serious training.

This is where curcumin comes in. The active compound in turmeric, curcumin has been shown in multiple trials to reduce markers of exercise-induced muscle damage, lower inflammatory cytokines, and reduce post-exercise muscle soreness — without blunting the underlying adaptation response the way NSAIDs can.^[4] Our full article on inflammation in runners and how curcumin can help covers the evidence in detail.

There's an important caveat though: standard curcumin has terrible bioavailability on its own. That's why the form matters. RunStrong uses Curcumin C3 Complex®, a patented extract standardised for three curcuminoids — not generic turmeric powder. And why it matters is covered in the next section. For a full comparison, see our article on curcumin vs turmeric.

For more on what's happening in your muscles after hard sessions, our article on post-exercise muscle soreness gives a useful breakdown of the physiology.

3. Fat Oxidation Efficiency — The Engine Your Aerobic Base Runs On

Every runner has a finite supply of glycogen — roughly 90 minutes' worth at moderate intensity. Beyond that, the body must increasingly rely on fat as fuel. The better your body is at oxidising fat during exercise, the longer your glycogen stores last, the more evenly you can pace, and the less dramatically you hit the wall in a marathon.

L-Carnitine is the molecule that physically transports long-chain fatty acids across the mitochondrial membrane, where they can be burned for energy. Without adequate carnitine, fat oxidation is impaired regardless of how good your aerobic base is. The challenge is that most of the body's carnitine is stored in muscle tissue, and research has shown that muscle carnitine content can be increased through consistent supplementation — improving fat utilisation during exercise and reducing reliance on glycogen.^[5]

This isn't just about marathon running. Improved fat oxidation at lower intensities means more efficient easy runs — the foundation of any training programme. For more on why most runners are doing their easy runs too hard and how fat oxidation connects to that, see our piece on the science of easy running.

L-Carnitine also plays a direct role in recovery — it reduces oxidative stress in muscle tissue after exercise, which is why studies have found it reduces muscle soreness and speeds up repair between sessions. You can explore the full picture in our deep-dives on what L-Carnitine actually is and its role as the endurance enhancer.

4. Vitamin D — The UK Runner's Silent Problem

Around one in five people in the UK have low vitamin D levels, according to data from the National Diet and Nutrition Survey.^[2] For runners who train early in the morning, late in the evening, or through autumn and winter — which is essentially all UK runners for at least six months of the year — the risk is substantially higher. Between October and April, the angle of the sun in the UK means that UVB radiation is insufficient to trigger meaningful vitamin D synthesis in the skin, regardless of how much time you spend outdoors.

For runners, this matters far beyond immune function. Vitamin D plays a critical role in bone mineral density, and low levels significantly increase the risk of stress fractures — one of the most debilitating injuries a runner can suffer. Stress fractures aren't just caused by training too hard too fast; they're caused by bone that can't remodel and strengthen quickly enough to keep pace with the mechanical load of running. Vitamin D is central to that remodelling process. Our article on stress fractures — the nightmare injury explains this in detail.

Vitamin D also modulates the immune system and plays a role in muscle function, which is why deficiency is associated with higher rates of upper respiratory infections — the training-disrupting colds and chest infections that seem to cluster in winter. The NHS recommends all UK adults consider taking a vitamin D supplement between October and March, but for runners the case for year-round supplementation is strong. Read the full evidence base in our article on Vitamin D3 for runners, or start with the basics of Vitamin D if you want the fundamentals first.

RunStrong uses vegan Vitamin D3 derived from algae — the same form the body synthesises from sunlight, and more effective than D2 at raising serum 25(OH)D levels.

5. Nutrient Absorption — The Problem That Undermines Everything Else

You can eat impeccably and still be under-nourished if your body isn't absorbing what you consume. This is the issue that most supplements — and most diet plans — completely ignore.

Curcumin is the most extreme example. On its own, curcumin has less than 1% oral bioavailability — it's rapidly metabolised and eliminated before it can reach the bloodstream in meaningful quantities. The solution, discovered in a landmark 1998 study, is piperine — the active compound in black pepper. When taken alongside curcumin, piperine increases curcumin bioavailability by up to 2,000%.^[6] Without it, the curcumin in your supplement is largely wasted.

But piperine's effects extend beyond curcumin. Research indicates it also enhances the absorption of a range of other nutrients — including B vitamins, selenium, and beta-carotene — by up to 30% through inhibition of intestinal enzymes that would otherwise break them down.^[6] In a supplement containing multiple nutrients, piperine isn't just an add-on — it's the ingredient that makes everything else work better. Our full article on what piperine is and why it matters covers the science.

RunStrong uses BioPerine® — the patented standardised piperine extract used in the original bioavailability research, not generic black pepper extract of variable quality.

Nutrition by Training Phase

Your nutritional needs aren't static across the training year. What your body requires during a high-mileage marathon block is different from what it needs in a recovery week, and getting this wrong — either underfuelling during heavy training or failing to support recovery afterwards — is one of the most common causes of accumulated fatigue, illness, and injury in amateur runners.

Base Building

Base building is the phase where aerobic infrastructure is laid down — the dense capillary networks, increased mitochondrial density, and cardiac adaptations that make everything else possible. This is where fat oxidation efficiency matters most, because the volume of easy, aerobic running in base phase is high, and your ability to fuel it efficiently from fat determines how sustainable that volume is without excessive fatigue.

Nutritional priorities during base building: adequate total calories (this is not the time to restrict), sufficient protein to support muscular adaptation (1.4–1.7g per kg of body weight per day is a reasonable target for distance runners^[7]), and consistent micronutrient intake — especially iron and vitamin D — to support the blood and bone adaptations that base training demands. See our article on optimising protein intake for running for specific guidance.

Peak Training and Marathon Blocks

This is the most nutritionally demanding phase, and the most common time for things to go wrong. Training volume and intensity are both high, recovery windows are short, and the cumulative inflammatory and oxidative stress on the body is at its peak. This is precisely when iron depletion accelerates, anti-inflammatory capacity is most stretched, and immune function can start to dip.

Carbohydrate needs are at their highest during this phase — especially around hard sessions. Pre-session carbohydrates fuel quality work; post-session carbohydrates help replenish glycogen and support recovery. For race-specific fuelling strategies around the marathon itself, our deep-dive on marathon fuelling and recovery — what to eat before, during, and after 26.2 miles is the most comprehensive resource we've produced.

During a marathon block, the case for daily supplementation is strongest. The gap between what your body needs and what diet reliably provides is at its widest exactly when the consequences of deficiency are most severe.

Taper

Many runners feel dreadful during taper — flat, heavy-legged, and oddly anxious. Some of this is psychological, but some is genuinely physiological: the sudden reduction in training volume means the body is absorbing more of the nutrients it's been routinely depleting. Continue eating well; don't fall into the trap of cutting calories because you're running less. The goal during taper is to top up glycogen stores, allow inflammation to resolve, and arrive at the start line with full reserves.

Iron and Vitamin D levels can still be building during taper — particularly if you've added them to your routine mid-block. This is also a good time to focus on sleep, which is where much of the repair and restoration happens. Our article on sleep and running recovery covers why it matters and how to protect it in the pre-race period.

Recovery and Off-Season

The period after a big race is when many runners catastrophically under-recover. Training stops abruptly, nutrition often drops off simultaneously, and the body is left trying to repair significant accumulated damage without the raw materials it needs. Post-marathon immune suppression is real — the so-called "open window" period where infection risk is elevated can last several weeks.

Recovery nutrition should prioritise protein (for muscle repair), iron (to address the significant haemolysis losses of race day), and anti-inflammatory nutrients. This is also when athletes coming back from injury need the most support — our article on coming back from injury: a runner's nutrition guide addresses this specifically. For older runners — the growing cohort of over-40s who represent a huge proportion of UK club runners and marathon participants — recovery needs are amplified further. See our guide to running after 40: what changes and how to adapt.

Common Nutritional Mistakes Runners Make

Even experienced runners make the same nutrition errors repeatedly. These are the ones that have the biggest impact on performance and health.

• Treating race-day fuelling as the whole nutrition story. Gels are a short-term emergency fuel supply. They keep you moving during a race; they don't build the physiological capacity to run the race in the first place. Runners who obsess over race nutrition while neglecting daily nutrition are putting a turbocharger on a poorly maintained engine.
• Ignoring slow-burn deficiencies. Iron deficiency and vitamin D insufficiency don't announce themselves dramatically. They erode performance gradually over months — declining paces, persistent fatigue, more frequent illness — in ways that are easy to attribute to overtraining, undertraining, stress, or bad luck. By the time the deficit is obvious, significant ground has been lost.
• Relying on generic multivitamins. Standard multivitamins use generic, cheap forms of ingredients — ferrous sulphate instead of iron bisglycinate, plain turmeric instead of standardised curcumin extract — and often in doses too small to be meaningful. A supplement designed for runners is fundamentally different from a supplement designed for the general population.
• Using NSAIDs as a recovery tool. Ibuprofen has become almost normalised in running culture — taken before long runs, after hard sessions, around race day. But regular NSAID use suppresses the inflammatory response that drives training adaptation, damages the gut lining, and may actually impair muscle protein synthesis. It treats the symptom (soreness) while undermining the system (recovery and adaptation). Curcumin provides meaningful anti-inflammatory effects without these downsides.
• Eating less during high-mileage training. Some runners, particularly those with weight-loss goals, attempt to use marathon training as an opportunity to restrict calories. This is a recipe for injury, illness, and underperformance. High training loads demand high energy intake — restrict calories and you restrict recovery.

Daily Supplement Foundation vs Race-Day Fuelling — Complementary, Not Competing

One point worth emphasising clearly: daily nutrition and race-day fuelling are solving entirely different problems, and neither replaces the other.

Race-day nutrition — gels, energy drinks, electrolyte tabs, bananas at mile 20 — exists to top up blood glucose during prolonged exercise, delay glycogen depletion, and replace electrolytes lost through sweat. It operates on a timescale of hours. Without it, you'll hit the wall. With it, you can maintain intensity longer. The science here is well established and the major sports nutrition brands have it largely sorted.

Daily nutritional support — the kind that addresses iron status, inflammation, fat oxidation efficiency, vitamin D levels, and absorption — operates on a timescale of weeks and months. It builds the physiological infrastructure that determines how fast you can run, how well you recover between sessions, how resilient you are to injury, and how effectively your body responds to training. You can't gel your way out of iron deficiency. You can't carb-load your way to better fat oxidation. These are built slowly, through consistent daily habits.

Think of it this way: race-day fuelling is the petrol in the tank. Daily nutrition is the condition of the engine. Both matter. But most runners focus almost entirely on the petrol and barely think about the engine.

RunStrong sits firmly in the daily foundation category — it's a supplement you take every day, not before a race. The benefits accumulate over four to eight weeks of consistent use. It complements your existing gel and electrolyte strategy; it doesn't compete with it.

How to Build a Complete Runner's Nutrition Plan

A complete runner's nutrition plan has three layers. Each one builds on the one below it.

Layer 1: The Whole-Food Foundation

No supplement replaces a good diet, and no good diet can be reduced to supplements. The foundation should be a varied, wholefoods-based diet with:

• Sufficient total calories — especially during high-mileage phases. Under-eating is far more common among runners than over-eating, and far more damaging to performance.
• Carbohydrates as the primary fuel source — oats, wholegrain bread and pasta, rice, potatoes, fruit. These are not the enemy; they are the engine fuel.
• Adequate protein at 1.4–1.7g per kg body weight daily — from chicken, fish, eggs, dairy, legumes, tofu. Spread across meals rather than concentrated in one sitting for optimal muscle protein synthesis.
• Iron-rich foods where possible — red meat (haem iron, highest bioavailability), dark leafy greens, lentils, fortified cereals. Pair plant-based iron sources with vitamin C to improve absorption.
• Dietary fats from quality sources — olive oil, avocado, oily fish, nuts. Fat is not just a fuel; it's essential for hormone production and fat-soluble vitamin absorption.
• Plenty of colour — the antioxidants and phytonutrients in fruit and vegetables are the body's first line of defence against oxidative stress. Aim for at least five portions daily; more during heavy training.

Layer 2: Strategic Timing

When you eat matters almost as much as what you eat. Key principles:

• Eat carbohydrates before sessions lasting longer than 60–90 minutes.
• Consume protein and carbohydrates within 30–60 minutes after training to kickstart recovery.
• Avoid tea and coffee in the hour before and after iron-rich meals or iron supplements — tannins and caffeine inhibit iron absorption.
• Take supplements with food for best absorption; L-Carnitine in particular benefits from being taken alongside carbohydrates, which facilitate carnitine uptake into muscle tissue.^[5]

Layer 3: Targeted Daily Supplementation

Once the whole-food foundation is in place and timing is optimised, targeted supplementation fills the gaps that diet alone can't reliably cover — particularly for UK runners dealing with the specific depletion effects of high-mileage training and limited sunlight.

The five nutrients most runners need to address, and why, are covered in detail across our ingredient deep-dive articles:

• Iron — why runners are at risk and how deficiency steals performance
• Curcumin — the natural anti-inflammatory for runners and why the form matters
• L-Carnitine — the endurance enhancer and what it actually does
• Vitamin D3 for runners and the fundamentals explained
• Piperine — why it makes everything else work better

RunStrong combines all five of these in a single daily capsule serving — specifically formulated for runners, using patented, research-backed ingredient forms at meaningful doses. For a full breakdown of the formulation, dosing rationale, and how to fit it into your routine, the complete guide to RunStrong is the place to start.

References

1. Telford RD, Sly GJ, Hahn AG, Cunningham RB, Bryant C, Smith JA. (2003). Footstrike is the major cause of hemolysis during running. Journal of Applied Physiology, 94(1), 38–42.
2. Scientific Advisory Committee on Nutrition. (2016). Vitamin D and Health. London: Public Health England. Available at: www.gov.uk/government/publications/sacn-vitamin-d-and-health-report
3. Peeling P, Dawson B, Goodman C, Landers G, Trinder D. (2008). Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones. European Journal of Applied Physiology, 103(4), 381–391.
4. Hewlings SJ, Kalman DS. (2017). Curcumin: A Review of Its Effects on Human Health. Foods, 6(10), 92. doi.org/10.3390/foods6100092
5. Wall BT, Stephens FB, Constantin-Teodosiu D, Marimuthu K, Macdonald IA, Greenhaff PL. (2011). Chronic oral ingestion of l-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. Journal of Physiology, 589(4), 963–973. doi.org/10.1113/jphysiol.2010.201343
6. Shoba G, Joy D, Joseph T, Majeed M, Rajendran R, Srinivas PS. (1998). Influence of piperine on the pharmacokinetics of curcumin in animals and human volunteers. Planta Medica, 64(4), 353–356.
7. Thomas DT, Erdman KA, Burke LM. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528.