in Healthy Eating

Explained: Oxidative Stress, Free Radicals, Reactive Oxygen Species

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Oxidative stress, free radicals, and reactive oxygen species can be hard names to remember. However, remembering these names and what they do is crucial for a healthier life. Let’s see why.

Article Guide:

You may have heard any of these three being mentioned on several occasions, but you’ve never quite understood what they actually meant. Free radicals are often used in the same sentence with cancer, oxidative stress is a favorite buzzword for many nutritional supplement companies, and reactive oxygen species are rarely mentioned because they’re hard to pronounce.

Luckily for you, this article discusses all three of them. It also dives into their relationship and explains how it affects you through your food choices. While you may not be particularly familiar with either of these, understanding them will give you important insights into how and why substances with antioxidant properties work (and don’t work). Moreover, their implications in chronic inflammation will become clearer to you.


Reactive oxygen species (ROS)

Reactive oxygen species are highly reactive molecules which contain oxygen. Two examples of ROS are oxygen ions and peroxides, compounds containing an oxygen-oxygen single bond. ROS are created when we breathe; we spend oxygen from the environment and our cells start to produce energy. During this process a group of ROS, called free radicals, become synthesized.

ROS are usually a part of the natural defenses of our immune system. They are also produced during our everyday metabolic functioning. One must know, ROS have important roles in our homeostasis and normal cell signaling.

I’ve mentioned free radicals as one group of ROS. However, there are also non-radicals. Ozone is considered a ROS as well!


Free radicals, the bad guy?

Now, let’s talk a bit more about free radicals. I think there’s a new article being posted on the internet about free radicals and cancer almost every day.

Free radicals are atoms, ions, or molecules that have at least one unpaired electron in their structure, with certain ions and complexes being an exception. This mentioned unpaired electron starts feeling lonely after a while, which is why he wants to chemically react with other substances, sometimes they also react with themselves (I’m not joking and this is not a masturbation reference).

They usually target different victims, among which we can find:

  • Lipids

They cause lipid peroxidation, a degradation of lipids where their structure and function are affected.
Free radicals basically steal an electron from the lipid cell membrane which, as you might imagine, negatively affects it with them mentioned changes. Interestingly, polyunsaturated fatty acids are the group of fats most prone to this process, as a consequence of their chemical bonds.

  • Proteins

Free radicals aren’t satisfied with stealing only electrons from the lipid cell membrane. They also like to target the peptide chain, a chain linking multiple amino acids – the building blocks of protein. A similar thing happens in proteins as does with lipids – the structure and function of proteins is affected in a negative way.

  • DNA

If you thought stealing electrons from lipids and proteins isn’t bad enough, free radicals also like to alter our DNA molecules. The involved changes can cause mutations, they are also cancerous and terategenous. Neither of these changes is pleasant.

But there’s more to free radicals. When they are produced, oxidative stress occurs through the mentioned targets.


Oxidative stress

Oxidative stress is basically an imbalance between the natural production of free radicals and your body’s antioxidant defense mechanism. When free radicals overwhelm our antioxidant defenses, their ability to defend against these radicals, we can witness oxidation of important molecules (lipids, proteins, and DNA as I’ve mentioned).

An increase in oxidation of these molecules is associated with an important number of diseases, including inflammation. Under normal conditions, our body is well adapted to scavenge remaining ROS, thus maintaining their numbers at an ideal and manageable level.

At this point, it’s important to mention something hugely important. High levels of ROS aren’t necessarily bad in all cases. They can suppress the growth of tumors. Moreover, chemotherapy often kills cancer cells by increasing ROS stress. Typically, there is an inflammatory response which produces more free radicals in association with the oxidized molecules I’ve mentioned earlier.

But generally, higher levels of oxidative stress are considered undesirable for healthy cells. This is where the antioxidant capabilities of our body come in. This protein-controlled response is vital to maintain a enough balance of ROS in our bodies.

Namely, oxidative damage is the result of a higher oxidative stress baseline. And oxidative damage is implicated in a number of diseases, ranging from different types of cancer to Alzheimer’s disease, heart failure, and autism.

By now you might be wondering what causes oxidative stress. Given the knowledge what kind of blog this article is being written on, I think it’s rather obvious. However, another important source is cigarette smoke. And not only active smoking, passive smoking causes significant increases in oxidation of the mentioned molecules as well. Cigarette smoke causes a depletion in our body’s antioxidant defense mechanism.

Physical stress (working out) causes an increase in ROS too.

Wait, what? Are you advocating not to be physically active?

No, not really.

There is a slight and short-term increase in free radicals. It is believed this increase is a triggering mechanism or signal which allows our body to up regulate its natural antioxidant production. To put it in simple terms, you have an increase in free radicals which send a message to your body to increase the production of antioxidants. These counter the increase again and homeostasis reigns once more.
There is one more thing that needs mentioning in this mix – antioxidants.



As their name suggests antioxidants, are molecules which inhibit oxidation of other molecules. They are comprised of endogenous, produced by our body, and exogenous, we get them through our diet, antioxidants.

In the past it was believed food containing antioxidants are the Holy Grail against cancer. However, large clinical trials with limited numbers of antioxidants, by that I mean few antioxidants out of all available ones, suggested that supplementing with a few antioxidants in large numbers may actually be harmful.

There’s two important points to stress as far as antioxidants go:

  • They have a synergistic effect

You need to eat a variety of antioxidants for them to work correctly. Eating just blueberries for one antioxidant isn’t going to help much. Furthermore, vitamin C, E, and beta carotene contributes much less to your body’s antioxidant ability, if we compare them to the hundreds of different antioxidants found in a healthy diet.

  • Increasing amounts of antioxidants (through supplementation of isolated antioxidants) can be harmful for your body

Clinical trials which have used synthetic antioxidants for longer periods of time noted potential disturbances in the redox network of the bodies of participants.

It’s hard to summarize this post. I suggest reading it completely, as this is an important topic.

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