Find out how to fuel well for your runs – and for everyday life

When it comes to a runner's diet, it seems everyone has an opinion. But often this is based on what we can term n=1; that is, when an individual bases an outcome on their personal experience; or the science, when it is available, is simplified to take into account only fuelling and recovery.

But human bodies are not machines. While we need fuel to move and to survive, it is not a simple equation of being able to cover a certain number of miles when we fill our tanks with a specific amount of fuel. In human biology, the body is a series of intricate processes that interact and work with each other. This is why fuelling is never as simple as just energy in and energy out; it is about the composition of your diet, the timing of your nutrients and the quantities it takes not just to meet the demands of your training load, but also to drive essential biological processes alongside your running.

Making the right choices in your training, lifestyle and nutrition will help you to maintain your training effort day after day, encouraging adaptation, helping to maintain motivation and, ultimately, bringing the improvement you are looking for. It’ll keep you healthy, too. Studies have also shown that the timing of nutrition has an integral role to play in maintaining hormonal balance, boosting bone health and supporting your immune system.

What is the best runners' diet?

So how do you make the right choices? What you’ll find here isn’t a list of rules to follow. I am against food rules, because when people live by rules, it can become an obsession. And we all know how obsessive runners can be! Instead, you’ll find the information you need to inform and empower you to make the correct choices when it comes to your running – and day-to-day – nutrition. This is a guide you can learn from and adapt to your lifestyle; it’s a manual to fuel your running and your life...

Let's talk about carbs

runners diet
It takes around 500g of carbohydrate to fill your glycogen stores – which will last you for around 60-90 minutes of running d3sign - Getty Images

Carbohydrate is the critical fuel source for exercise, because it is broken down into glucose, which is the body’s preferred energy currency; this is then utilised by the body to provide energy. Carbohydrate is stored as glycogen in your liver and muscles, and the glycogen in muscle is the most readily available and quickly released energy. The catch, as you may know from long runs and the latter stages of marathons, is that this storage facility is limited. If muscles are inadequately fuelled, it leads to fatigue and poor performance, and may put you at greater risk of injury.

It takes around 500g of carbohydrate to fill your glycogen stores and, at most, this will last you for 60-90 minutes of running at 55-75 percent of your maximal heart rate. The faster you go, the sooner your stores will deplete. So for those of you training most days, your glycogen stores are always slightly depleted.

This makes it vital to plan carbohydrate intake around your training sessions; the amount you need will depend on the frequency, duration and intensity of your training.

Running on empty

Problems occur when runners aim to do hard sessions either deliberately fasted or in a carbohydrate-depleted state, owing to inadequate fuelling in the hours – or even the day – beforehand. Further difficulties can arise when they find they are not hungry immediately after a session, so they fail to properly fuel the recovery process, thereby compromising their recovery and adaptation. Both situations will have negative effects on hormonal regulation in the body. If this failure to refuel and repair continues, it can have long-term consequences on not just your running performance but also your overall health, such as a depressed immune system, a decrease in bone density and a much slower digestive system.

The hormone factor

A key hormone that can be affected by our exercise levels and eating habits is ghrelin, which is mostly produced in the stomach. Levels of our so-called ‘hunger hormone’ rise after exercise or several hours after a meal, telling us we need to refuel. When ghrelin is high, levels of another hormone – leptin – are low. Both hormones will return to normal levels when our energy demands are met. However, if a runner continually fails to fuel adequately after a training session, intentionally or unintentionally, leptin levels stay low. Chronic low leptin levels encourage the body to preserve energy, so you burn fewer calories and store more fat.

So, while the runner may think they are going to lose weight and improve body composition, the reverse can happen. It’s important to highlight here that this is a simplified version to help explain why some runners, even when they restrict calorie intake or increase training, still don’t achieve the body composition and weight goals they would expect.

Keeping your tank full for runs

runners diet
For runs longer than 60 minutes, aim for 30-60g of carbs per hour for the first three hoursPatrick McDermott - Getty Images

For runs longer than 60 minutes, aim for 30-60g of carbs per hour for the first three hours, increasing to 60-90g of carbs per hour if you’re still going after that. These can be in the form of sports products such as drinks, gels or bars, or actual food such as bananas and sweets. On longer runs over varying terrain, some runners may prefer food such as boiled, salted potatoes, noodle soup or even pizza.

Fuelling best practice

Gastric distress – including runners' trots – is one of the most common issues reported with taking on fuel when running. This leads some runners to avoid fuelling during long or intense training, despite the importance of carbohydrate availability. But these runners often refuel during a race in the search for optimal performance. When I ask why, the answer is usually bound up in the notion that they want to ‘save’ their energy for after training, so they have something to look forward to. This is one myth that needs to be busted. In fact, for optimal performance and recovery, fuelling before, during (on long runs) and after is best practice and actually helps with satiety and appetite.

In-run fuel should be in the form of glucose and fructose: the body can absorb around 60g of glucose per hour and 30g of fructose. Some studies suggest this limit of 90g could be increased to 120g in some athletes who train their gut, but the sample sizes used have been small and only involved men running at altitude. Whatever you choose, practise until you have nailed what works for you. Mistakes include:

1. Leaving it too long before fuelling; start taking on nutrition in he first 30 mins and then every 30-40 mins.

2. Taking gels too quickly; take one gel over 4-5 mins, not all in one go. This aids absorption and tolerance.

3. Becoming dehydrated and not replacing fluids and electrolytes, specifically sodium.

How to hydrate

Talking of dehydration, this is something that runners in particular should be wary of. It is well documented that fluid intake and adequate hydration are important during exercise, and critical over long training sessions and events. Along with maintaining hydration, fluid intake during endurance running helps to regulate body temperature (thermoregulation) and ensure adequate plasma (blood) volume.

Ensuring that plasma volume and thermoregulation stay within an optimal range has a direct impact on performance. When core body temperature rises owing to dehydration, plasma volume decreases, resulting in an increased heart rate, which accelerates fatigue.

Just a one per cent reduction in bodyweight through fluid losses can contribute to these negative physiological effects. In addition, dehydration has a marked effect on cognitive function, compromising your ability to make good decisions.

What about salts?

runners diet
Most electrolyte tablets, salt capsules or sports drinks provide 250-300mg of sodiumPeter Dazeley - Getty Images

Most runners will sweat between 400ml and 2,400ml per hour of exercise. The average is around 1,200ml per hour, but this varies with age, sex, weight, intensity of training and the temperature. Sweat is mostly water, but you also lose electrolytes, mainly sodium.

The sodium content of sweat varies, from 115mg per 1,000ml of sweat to more than 2,000mg. A runner who is a ‘salty sweater’ (high sodium) may lose more than the recommended intakes. Most electrolyte tablets, salt capsules or sports drinks provide 250-300mg of sodium. If you are diluting your electrolytes into 750ml, this will mean having to consume in the region of 2,250ml of fluid per hour in longer races to meet your sodium requirements, which is hard from a consumption and transportation point of view.

So, it’s little wonder that many runners complain of the symptoms associated with low sodium intakes and dehydration, such as gastrointestinal distress, nausea, bloating, fatigue, impaired concentration and dizziness. The biggest cause of mid-run stomach issues is related to sodium imbalance, not sports nutrition gels or bars. If you are dehydrated, and consuming glucose, it becomes highly concentrated in the gut. Blood is being directed away from the stomach to the working muscles, so the gut cannot absorb the glucose quickly enough, resulting in stomach upsets.

I usually suggest runners take in 700-900mg of sodium an hour during longer training runs and races. This can be a mix of salt tablets, electrolytes, energy drinks and even food if you can stomach it (eg salted peanuts, cured meat).

Sodium balance is not confined to when you are running; it is also important pre-training or leading up to an event. I often suggest runners start drinking electrolytes in the 24 hours before race day to help prevent the issues above.

Fat facts

runners diet
Opt for good fats – from foods such as peanut butter and oily fish – over saturated varietiesMichelle Arnold / EyeEm - Getty Images

Not all fat is bad for you. You need some fat to help absorb the fat-soluble vitamins A, D, E and K, and to provide essential fatty acids the body cannot produce itself. These nutrients are important for recovery, immune health, inflammation and prevention of fatigue. Fat should be an integral part of your diet, but should be avoided as an immediate fuel source – high-fat foods pre-run will slow digestion.

Not all fats are good, either. Eating too much saturated fat can raise levels of harmful cholesterol, which increases your risk of heart disease. Sources include pies, cakes and biscuits, fatty cuts of meat, sausages and bacon. The term also encompasses trans fat, which is often found in processed foods. To up your intake of the good stuff, aim for the following:

• Oily fish, such as salmon and mackerel, for omega-3s

• Nuts and seeds, including their oils and butters

• Sunflower and olive oils

• Avocados

I encourage runners to choose good fats over saturated varieties. However, these fats still have a high energy value and should be eaten with that caveat in mind.

Why protein counts

runners diet
Amino acids are found as a complete source in animal-protein food such as dairy, meat, fish and eggsAlexander Spatari - Getty Images

Proteins are often called the building blocks of the body. Protein consists of combinations of structures called amino acids. There are 20 amino acids and these combine in various sequences to make muscles, bones, tendons, skin, hair and other tissues. They serve other functions, as well, including transporting nutrients and producing enzymes.

Eight of these amino acids are essential and must come from your diet. They are found as a complete source (containing all essential amino acids) in animal-protein food such as dairy, meat, fish and eggs. They are found as an incomplete source in plant-based proteins; that is, they will be lacking in one or more of the essential amino acids. Examples include vegetables, grains, nuts and legumes. If, however, these are combined in the correct way, you can make a whole source of protein. Some good combinations include baked beans on toast; rice and dhal; or a wholegrain bagel with peanut butter.

We in the sports and fitness industry hear a lot about protein, with many believing it is the most important macronutrient for active people. In reality, runners need protein primarily as a response to exercise rather than as a fuel source.

Protein has been a huge area of research for many years, with the most recent findings demonstrating how important it is in the recovery phase. During exercise, whether that’s endurance sports such as running and cycling, team or power sports such as netball, football and tennis, or resistance training (using weights), there is an increase in the breakdown of protein in the muscle. There is a preference to include a large amount of protein in the immediate recovery phase, but the recommendation for protein foods is that they should be distributed evenly throughout the day, to help counteract a negative protein balance. The suggested amount is 0.4g/kg bw protein four to six times a day depending on training load.

For a 65kg runner, this will be 26g protein at each serving, which looks like:

  • 4 medium-sized eggs

  • 100g chicken

  • 100g red meat

  • 300g tofu

  • 250g Greek yoghurt

  • 150g chickpeas

What about the small stuff?

Along with macronutrients – carbs, protein and fat –micronutrients are vital for many metabolic processes. You need to get them from your diet. They include:

Vitamins A, B, C, D, E, K

Minerals Calcium, iron and phosphorus

Electrolytes Sodium and potassium

Trace elements Iodine, zinc and magnesium

Most micronutrients function as co-enzymes or co-factors – that is, they aid enzymes and proteins in their function. For example, the B vitamins are needed for carbohydrate and fat metabolism; while vitamin C, along with zinc, is important for a healthy immune system; and magnesium and calcium are vital for good muscle contraction. All are needed to keep you healthy and ensure you run at your best.

Supplementary benefits?

Do runners need more minerals and vitamins? Do you need supplements? The research is inconclusive. Some studies show enhanced requirements in runners because of an increase in damage to muscles by free radicals, which accumulate in response to exercise. (Lifestyle factors, such as smoking, also lead to the excessive production of free radicals.) But there have been no proven links to improved sporting performance from a diet high in free-radical-fighting antioxidants.

The quality of your diet is crucial. As an active person, you should naturally be taking in more food to fuel your running, and as long as this fuel is balanced and nutrient-rich, you should meet your increased requirements. If you eat a balanced diet that includes wholegrains, veg, meat, fish and dairy, you should have no problem getting all you need.

Red meat and eggs are your best sources of iron; plant-based options, such as green, leafy vegetables, pulses, wholegrains and fortified cereals are harder to absorb than animal sources and must be taken with vitamin C to enhance absorption. While dairy is your best source of calcium and phosphorus, soya products and oily fish are also good sources.

One nutrient to be aware of is iodine; with the rise in the use of plant-based milks, most of which don’t have added iodine, some people risk deficiency, which can lead to metabolic problems. Also, vegan and vegetarian runners may need to pay special attention to iron and B12, which can be hard to get from a plant-based diet.

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