INTRODUCTION
Last lesson, we zoomed out. We looked at three biological forces that constantly shape what happens inside your body: acid–base balance, inflammation and oxidative stress. None of them is inherently bad. In fact, you need all three.
But biology has a recurring theme: Useful processes become problematic when they lose their balance.
This week, we zoom in on oxidative stress. And to understand it, we first need to clear up one of nutrition's favourite misunderstandings. Oxidation is not something your body is desperately trying to avoid. It is happening inside you right now. Constantly.And that is perfectly normal. The trouble begins when a useful bit of chemistry gets out of control.
WHAT YOU'LL LEARN
By the end of this lesson, you should understand what oxidative stress actually means, where reactive oxygen species come from, why your body deliberately produces some of them, how they can damage cells when their levels become excessive, and why antioxidant defence is much more sophisticated than simply eating more "antioxidants."
1. LIFE RUNS ON OXYGEN
Take a breath.
The oxygen you just inhaled will eventually help your cells extract energy from the food you eat. That happens mainly inside tiny cellular power stations called mitochondria. It is one of the great chemical tricks of life. Oxygen allows us to produce energy very efficiently.
There is, however, a small complication.
Whenever oxygen participates in metabolism, some reactive oxygen-containing molecules can also be formed. Collectively, many of these molecules are referred to as reactive oxygen species, or ROS.
Think of a fireplace. A controlled fire can heat your house, cook your food and make a dark Belgian winter considerably more pleasant. But fire also produces sparks.
Your metabolism is somewhat similar. Energy production is useful. Sparks come with the territory.
2. MEET THE ROS FAMILY
You will often hear people use the words free radicals and reactive oxygen species as if they mean exactly the same thing. They don't. Free radicals are molecules or atoms containing an unpaired electron, which can make them highly reactive.
ROS is a broader family. Some ROS are free radicals. Others are not. Hydrogen peroxide, for example, is a reactive oxygen species but technically not a free radical.
Fortunately, there will be no exam ;)
What matters is the principle: your body continuously produces reactive molecules capable of interacting with other molecules around them. And at the right concentration, in the right place and at the right time, that is not a mistake. It is biology.
3. YOUR BODY ACTUALLY USES THEM
For a long time, reactive oxygen species were mainly presented as unwanted by-products of metabolism. Molecular troublemakers. Tiny vandals running around damaging cells. We now know that picture is far too simple.
At controlled levels, ROS are used as signalling molecules. They help cells communicate, respond to their environment and adjust their behaviour. Your immune system can also deliberately generate reactive molecules to help destroy invading microorganisms.
In other words: your body doesn't merely tolerate reactive molecules. It uses them. That changes the entire story. The goal of antioxidant defence cannot therefore be to eliminate every reactive molecule.
That would be like disconnecting your fire alarm because it makes noise. Sometimes the signal is the point.
4. EXERCISE: A BEAUTIFUL EXAMPLE
Exercise provides one of the clearest examples. When you exercise, your muscles temporarily increase their production of reactive oxygen and nitrogen species. That sounds bad. It isn't necessarily.
Those molecules participate in signalling pathways that help the muscle adapt to the challenge. They are involved in processes linked to mitochondrial adaptation, tissue remodelling and the strengthening of cellular defence systems.
The stress is temporary. The body responds. And afterwards, the system can become better prepared for the next challenge. This phenomenon is part of a broader biological principle called hormesis: A little stress can trigger adaptation.
It is one reason why "stress" should not automatically be translated as "damage." The dose, duration and context matter.
5. SO WHAT IS OXIDATIVE STRESS?
Now we can define it properly. Your body is constantly balancing the production of reactive molecules with systems that control them, use them, neutralise them and repair the damage they may cause. When oxidant production becomes excessive, or when the body's control and defence systems are insufficient to manage it, that balance can shift.
That state is called oxidative stress.
Modern redox biology makes an important distinction here. Physiological levels of oxidants can participate in normal signalling — sometimes described as oxidative eustress — whereas excessive or poorly controlled oxidant activity can produce oxidative distress and molecular damage.
So oxidative stress does not mean: “A free radical appeared.” It means something closer to: The system is losing control of the sparks. That distinction matters.
6. WHERE DO THE SPARKS COME FROM?
Some reactive molecules are generated simply because you are alive. Mitochondrial metabolism contributes to their production. Immune cells can generate them deliberately. Various enzymes also produce ROS as part of normal cellular chemistry.
But external factors can add to the oxidative burden too. Ultraviolet radiation, cigarette smoke, air pollution and certain environmental exposures can increase the production of reactive species or the molecular damage associated with them.
And then there is inflammation. As we saw last lesson, inflammation and oxidative stress are not separate little departments operating on different floors. Activated immune cells can produce ROS. Reactive molecules can in turn influence inflammatory signalling. They talk to each other. Sometimes rather loudly. That is why chronic biological stress tends to behave more like a network than a collection of isolated problems.
7. WHEN SPARKS START HITTING THINGS
A reactive molecule doesn't know whether the molecule next to it is important. If reactive species accumulate beyond what the cell can control, they can interact with the structures around them. They can modify lipids, including those in cellular membranes. They can modify proteins, potentially changing their structure or function. And they can contribute to DNA damage.
Cells are not helpless when this happens. They possess extensive maintenance, antioxidant and repair systems, and oxidative damage is continuously being detected, processed and repaired. So one damaged molecule is not a biological catastrophe. Your body repairs molecular damage every day.
A better analogy is maintenance on a house. A scratch in the paint? No problem. A loose roof tile? Fix it. A cracked window? Replace it. But imagine that the damage starts occurring faster than the repair crew can keep up. Day after day. Year after year. Now the situation changes.
Oxidative stress is therefore not just about damage. It is about the balance between challenge, defence, adaptation and repair.
8. MEET YOUR ANTIOXIDANT DEFENCE SYSTEM
At this point, nutrition articles often introduce blueberries. We are going to make you wait a little longer.
Because some of the most important antioxidant protection in your body is produced by your body itself. Cells contain sophisticated antioxidant systems involving enzymes and small molecules such as superoxide dismutase, catalase, glutathione peroxidases, peroxiredoxins and glutathione.
Different components work on different reactive molecules and in different parts of the cell. It isn't one giant antioxidant sponge. It is a network.
Imagine a city fire department. One team detects smoke. Another extinguishes fires. Another repairs damaged buildings. Another investigates what started the fire.
Your antioxidant systems work in a similarly coordinated way. And crucially, many parts of that system depend on nutrients.
9. NOW NUTRITION ENTERS THE STORY
This brings us back to the question we have been asking since Lesson 1: What does your body actually need?
Antioxidant defence requires raw materials.
For example, antioxidant enzymes depend on micronutrients such as selenium, zinc, copper and manganese, while vitamins such as vitamin C, vitamin E and riboflavin contribute to protection against oxidative stress through different mechanisms.
This isn't merely nutritional folklore. Within European food law, authorised health claims explicitly recognise that vitamin C, zinc, selenium, copper, manganese and riboflavin contribute to the protection of cells from oxidative stress when the food meets the required conditions for the claim.
Vitamin E is particularly interesting because it helps protect lipids in biological membranes from oxidative damage, while vitamin C can help regenerate the reduced form of vitamin E.
And suddenly our earlier lessons start joining together.
- Proteins provide amino acids.
- Minerals serve as cofactors.
- Vitamins participate in reactions.
- Water provides the environment.
- Energy metabolism produces the sparks.
- And antioxidant systems help keep those sparks under control.
Nutrition isn't a collection of isolated nutrients. It is chemistry supporting chemistry.
10. WHAT ABOUT ANTIOXIDANTS IN FOOD?
Plants contain thousands of compounds that can interact with our biology. Among them are vitamin C, vitamin E, carotenoids and a huge variety of polyphenols and other phytochemicals. This is one reason why diets rich in vegetables, fruit, nuts, seeds, legumes and other plant foods are nutritionally interesting.
But here comes an important correction to one of nutrition's favourite slogans. More antioxidants does not automatically mean more health.
The human body is not a glass of apple juice that we are trying to stop from turning brown. Reactive molecules also carry signals. Completely suppressing those signals would not necessarily be desirable.
And clinical studies with large doses of antioxidant supplements have produced much less spectacular results than the simple "free radicals bad, antioxidants good" theory would predict. Large supplemental doses may also interfere with normal cellular signalling and defence responses in some contexts.
This is an important distinction: Food and antioxidant pills are not the same biological experiment.
Eating a varied diet that supplies the nutrients required for normal antioxidant defence is one thing. Trying to flood the body with enormous quantities of one isolated antioxidant is another.
11. DON'T FIGHT OXIDATION. BUILD RESILIENCE.
This leads us to a more useful way of thinking about oxidative stress. The goal is not to create a body in which oxidation never happens. That body would also be dead.
The goal is to maintain the ability to generate signals when useful, control reactive molecules when necessary, repair damage when it occurs and adapt to challenges over time.
In other words: The goal is resilience.
Nutrition contributes by supplying the molecules and micronutrients those systems require.
Physical activity can stimulate adaptive responses.
Adequate recovery and sleep support normal physiology.
And reducing unnecessary sources of oxidative burden — such as smoking or excessive UV exposure — removes challenges your body simply does not need.
It is much less glamorous than buying a bottle labelled SUPER ANTIOXIDANT 12,000™.
Biology is inconsiderate like that.
WHAT SHOULD YOU REMEMBER?
Oxidation is part of life. The use of oxygen and normal cellular metabolism inevitably involve reactive molecules. Reactive oxygen species are not simply enemies. At controlled levels, they participate in signalling, immune defence and adaptation. Oxidative stress is a problem of balance. It develops when oxidant activity exceeds the body's ability to regulate it and repair its effects. Your antioxidant defence is a network. Enzymes, glutathione, vitamins, minerals and other molecules work together rather than acting as one universal radical sponge. Nutrition supports the system. The objective is not to eliminate every reactive molecule. It is to give the body what it needs to maintain control and resilience.
And perhaps most importantly: **Don't try to extinguish every spark. Build a body that knows what to do with them.**
NEXT WEEK
Reactive molecules can activate inflammation. Inflammation can generate more reactive molecules. Very useful processes can suddenly begin keeping each other alive.
So what happens when an immune response that was designed to protect us...
refuses to switch off?