Are you eating “too” healthy?

Have you ever wondered how your body responds to intense training at the cellular level? With this post, we aim to increase the understanding of how oxidative stress affects adaptations during endurance training for cyclists and why a too high focus on eating “healthy” actually can harm your performance.

Oxidative stress – friend or foe in endurance training?

Let’s start by diving into a study published in 2021 that highlights what really happens inside your body when you push through a hard training session. Beyond the burning legs and heavy breathing, your cells are buzzing with activity—and one of the key players in this process is something that might sound harmful at first – oxidative stress – caused by an overproduction of reactive oxygen species (ROS).

Exercise itself naturally generates ROS, acting as a training signal. For example heat is another factor that can amplify this response, as this research has shown. When you train in warmer conditions, your body temperature rises, increasing ROS production and further boosting adaptation. This is one reason why heat training has gained traction as an effective method to complement traditional endurance training.

Oxidative Stress: The double-edged sword

For years, oxidative stress was viewed as purely negative. The narrative was simple: ROS damage cells, and therefore limit performance and health. But research in the last few decades has flipped this view. ROS are not just destructive byproducts; they’re also powerful signals that drive many of the positive adaptations endurance athletes rely on, such as:

• Mitochondrial growth and function – more and bigger “power plants” in your muscles

• Capillarization – more tiny blood vessels delivering oxygen and nutrients where you need them most

• Improved insulin sensitivity – helping your body use energy more efficiently

In other words: without a certain amount of oxidative stress, your training wouldn’t be nearly as effective.

Antioxidants – hero or villain?

A colorful, nutrient-rich diet is without doubt a cornerstone of health and performance. But when it comes to antioxidants, more isn’t always better. While it’s nearly impossible to “overdose” through normal food, supplements are a different story. High doses of antioxidant supplements—especially vitamins C and E—have repeatedly been shown to blunt training adaptations by reducing the signaling role of ROS.

The takeaway? Prioritize whole foods, and be cautious with supplements. What seems protective in theory might actually get in the way of progress.

Nutrients vs energy

A dietary base of nutrient rich foods is a super important foundation, but only up to a certain threshold. After you’ve met your nutrient needs, a too strong focus on nutrient dense foods can actually be detrimental to performance. Why? Because nutrient dense foods are often sparse on energy, which athletes need to meet the energy needs required to fuel training and adaptations. We recently wrote a blog post on relative energy deficiency in sport (REDs). After eating plenty of things like berries, beans, fruit, fish, grass fed meat, lentils, nuts, vegetables and other nutrient rich foods, the rest of the energy needs are most easily met with things like sweets, Nutella, juices, oils/fats.

Bottom line, after a solid base of traditionally “healthy” food, eating more of it can be counterproductive. This increases the risk of not meeting the energy needs and if you add antioxidant supplements to this mix you might be harming performance in two ways.

Practical tips for cyclists

• Eat the rainbow: Aim for a variety of colorful fruits and vegetables each day instead of relying on antioxidant supplements.

• Skip the “megadoses”: Be cautious with high-dose vitamin C and E supplements—focus on food first.

• Nutrient AND energy: Start with a base of nutrient rich foods and then add energy dense foods to meet your energy needs.

• Include heat strategically: Add occasional heat training sessions (indoors or outdoors) when conditions allow, but balance them with recovery.

• Don’t fear the burn: See tough training sessions as opportunities for your body to adapt and grow stronger.

• Balance stress and rest: Adaptation happens between sessions, so give your body time to recover.

Wrapping it up

Simply put, oxidative stress influences endurance training adaptations in cyclists, and is not the enemy it was once thought to be. It isn’t simply “good” or “bad”—it’s about balance. Too much, and it becomes damaging. Too little, and you lose out on key adaptations.

Therefore, by:

• embracing oxidative stress through well-structured training (and occasionally in the heat)

• nourishing your body with a varied, whole-food diet, without excessive focus on nutrient dense foods

• making sure you eat enough energy

• avoiding antioxidant supplements

… you set yourself up for greater performance gains while staying healthy in the long run.