The engine behind your performance
To understand why nutrition is so important, it helps to look at the basics. “We have three key macronutrients: carbohydrates, proteins, and fats,” Van der Zwaan explains. “Proteins mainly act as building blocks—important for recovery and muscle development. But when it comes to performance, carbohydrates are the key.”
Carbohydrates are the main fuel during intense exercise—and that’s where the challenge lies. “Your body only has a limited supply of carbohydrates,” she says. “In well-trained athletes, that supply is depleted after about an hour and a half. After that, you simply can’t maintain the same intensity.”
Or, as many runners know it: hitting the wall. “That moment when you suddenly have no energy left often happens because your carbohydrate tank is empty,” Van der Zwaan explains. “And that applies just as much to recreational runners.”
When should you eat while running?
For those preparing for the Marathon Groningen—or the half marathon or 10 km on May 31—timing is crucial. “Don’t just look at distance, but especially at duration,” Van der Zwaan advises. “If you’re running longer than an hour, you really need to start thinking about nutrition during your run.”
An important detail: don’t wait until it’s too late. “You want to prevent that tank from running empty. So start eating within the first half hour.” What you eat differs from person to person. “Running makes eating more difficult because everything is moving. That’s why my main tip is: practice this during your training.”
From gels to bananas, from dates to a simple muesli bar—it can all work. “As long as it contains carbohydrates and works for you.”
Drinking: underestimated but crucial
In addition to nutrition, hydration is essential. “Especially over longer distances, dehydration plays a major role in performance loss,” Van der Zwaan says. “Even a small percentage of fluid loss can already have an effect.”
However, drinking only water is not always the best option. “Your body absorbs fluids better when they also contain sugars and salts,” she explains. “That’s why isotonic drinks work best.”
This doesn’t have to be complicated or expensive. “You can make it yourself: a bit of lemonade syrup, water, and a pinch of salt will already get you a long way.”
Recovery: where the gains are made
What you do after running is just as important as what you do during it. “Training is essentially about breaking your muscles down a bit,” says Van der Zwaan. “After that, you want them to come back stronger. That process is called supercompensation.”
Without proper recovery, progress stalls. “If you don’t eat enough after a workout, your recovery suffers and you risk overload or fatigue.”
Fortunately, the solution is simple. “Make sure you get a combination of carbohydrates and proteins after your exercise. This can be a full meal, but also something small like yogurt with muesli and fruit, or a sandwich with toppings.”
And that tempting post-run drink? “Hold off for a bit,” she advises. “Recovery first, then maybe a beer.”
Start with the basics
For many runners, the biggest gains don’t come from expensive supplements or complicated plans, but from the basics. “Don’t skip meals and eat a varied diet,” Van der Zwaan says. “Think vegetables, fruit, and whole grains. Basically: just eat normally.”
It sounds simple, but in practice, this is often where things go wrong. “The most common mistake is that people don’t eat enough—especially when they start training more.” Signs like fatigue, poor recovery, or “heavy legs” can point to this. “The first step is often simply: eat a bit more.”
Three tips for runners
Van der Zwaan concludes with three concrete pieces of advice for anyone training for the Marathon Groningen:
Train your nutrition as well
“Practice what you eat and drink during your training. You don’t want surprises on race day.”
Eat on time during your run
“Start after half an hour and aim for about two snacks per hour during longer distances.”
Build a strong foundation
“Three solid meals a day and enough carbohydrates make the difference.”
And perhaps the most important tip: don’t keep struggling with nutrition questions or concerns on your own. “If you notice that nutrition causes a lot of stress or you’re unsure what’s right, seek help,” says Van der Zwaan. “A sports dietitian can easily take a look with you.”
Series leading up to the Marathon powered by Campus Groningen
This article is the final part of a short series by Campus Groningen about preparing for the Marathon Groningen powered by Campus Groningen on May 31, 2026. In this series, we share tips, stories, and insights from runners, trainers, and experts on both the physical and mental aspects of running, so participants can start well-prepared and confident. Read more:
The article on mental preparation for a marathon
The article on the purpose of the marathon’s fundraising
The article about the ACLO running clinics: Join the Ride
The article on the social and economic impact of the marathon
