The Good and the Bad about Oxidation: What Happens When Oxygen Metabolizes?

March 10, 2024 9 min read

The Good and the Bad about Oxidation: What Happens When Oxygen Metabolizes?

Your body, your temple, but to sustain it you need oxygen, and without this 8 electron, 8 proton, 8 neutrons, and 2 atom molecule, you would not exist full stop. Luckily, oxygen is present in the atmosphere in some abundance, allowing you to breathe. However, this process creates byproducts; oxidants (the Bad), antioxidants (the Good), and the potential for cell mutation through oxidative stress (the Ugly). All these products bring a whole new half to this game of life.

How does this magical process that brings life, but is also temperamental, work? And what do we mean by oxidants, antioxidants, and oxidative stress? Join us, as we enter this fascinating world and discover just what it all means and how this interlinks with your gut.

Understanding oxygen homeostasis

Before we begin, we should explain the importance of oxygen for your body and why it needs to be balanced.

Oxygen homeostasis describes the balance of the required amounts of oxygen, both delivery and consumption within the cells, to support normal physiological functioning. Too much or too little can lead to the oxidisation of proteins, lipids, and nucleic acids and processes that can lead to cell dysfunction, mutation, and possible death[i][ii].

Oxygen is critical for cellular respiration, or the generation of energy in the form of adenosine triphosphate (ATP). As you take each breath of oxygen, it is distributed around the body via the blood. As it circulates, part of your mitochondria, the powerhouse of each of your cells, called the mitochondrial electron transport chain (ETC) intercepts it with a list of metabolic demands.

The ETC involves several protein complexes that are involved in the transfer of electrons through various redox reactions. Oxygen is a major part of this because it is the final electron acceptor in the ETC. Therefore, oxygen homeostasis and the ETC are intrinsically linked because it is an important substrate within it. And both are critical to sustain life[iii].  

Reactive Oxygen Species (ROS)

Reactive oxygen species (ROS) are reactive molecules that contain oxygen. Reactive oxygen species are a normal aspect of cellular metabolism, and usually, their levels are tightly regulated. Some ROS are important for roles, such as protecting the body from pathogens or cell signaling. But in excess, ROS can be harmful.

For example, if ROS build up, they can release oxidants, some of which are reactive free radicals. These increase in number and can become problematic. In an ideal world, the cell will have the capability to react with an antioxidant response. If the cell fails to achieve this, oxidative stress increases and cell dysfunction begins[iv].

What is the difference between oxidants, free radicals, and antioxidants?

Oxidants are molecules that are produced during the multiple reactions that take place during the interaction between the mitochondria electron transport chain and oxygen. These can be electron paired or accept electrons from other substrates. If they are unpaired, they are prone to running around highly reactive wanting to give or take an electron from other molecules to find stability. Often, oxidants stabilise themselves by stealing electrons from another weak cell, destabilising them, and causing damage. These oxidants are termed free radicals[v][vi].  

What factors can trigger free radicals?

Free radicals are triggered for a variety of reasons by both external and internal factors.

External factors include:

  • Air pollution
  • Tobacco smoke
  • Medication
  • Radiation
  • Ultraviolet rays

Internal factors include:

  • Everyday metabolic processes
  • Natural production from the body in response to invading pathogens
  • Illness
  • Injury
  • Stress
  • Exercise


Antioxidants, on the other hand, are compounds that can neutralise an unstable free radical. This process switches the free radical off and breaks the chain reaction that could lead to cell damage and oxidative stress. Antioxidants do this by donating an electron to the oxidant, which in effect neutralises the oxidant and at the same time destabilises itself.

Technically, this means the antioxidant assumes the title of free radical. However, the antioxidants can accommodate the changes in electron status and therefore, are not reactive or a danger to you[vii].

Where do we get antioxidants from?

Antioxidants can be produced by your body or acquired through external sources, particularly the food you eat. Some common sources of antioxidants include:

  • Vitamin C:bell peppers, broccoli, cantaloupe melon, cauliflower, green leafy veg, kiwi, lemon, oranges, strawberries, sweet potatoes, tomatoes
  • Vitamin E: almonds: avocado, green leafy veg, peanuts, spinach
  • Carotenoids: apricots, asparagus, broccoli, carrots, kale, mango, oranges, peaches, pink grapefruit, spinach, sweet potatoes, tomatoes, watermelon, winter squash
  • Phenolic compounds: quercetin (apples), catechin (berries, cocoa, tea), resveratrol (berries, grapes, peanuts, red and white wine), anthocyanins (blueberries and strawberries)
  • Selenium:barley, beef, Brazil nuts, brown rice, fish, poultry, shellfish
  • Zinc: beef, cashews, chickpeas, fortified cereals, oysters, pumpkin seeds, sesame seeds, shrimp[viii]

Understanding oxidative stress

Oxidative stress occurs when an imbalance between oxidants and antioxidants builds, with overwhelming numbers of free radicals being produced. This dysfunction leads to alterations in the cells, with the oxidisation of proteins, lipids, and nucleic acids, a state of oxidative stress begins. From here we are at risk of the beginnings of a myriad of illnesses and chronic diseases[ix][x].  For example, oxidative stress has been associated with:

  • Cardiovascular disease
  • Cancer
  • Neurodegenerative conditions e.g. Alzheimer’s and Parkinson’s Disease

But that’s not all. Oxidative stress can also affect the gut. For example, your gut bacteria can produce oxidative compounds, but they’ve also cleverly developed mechanisms to help resist an oxidative environment.

Oxidative stress is also implicated in the development of inflammatory bowel disease (IBD) as well as other gastric disease. We’ll take a deeper look into the effects of oxidants and the gut, next.

The Gut, Dysbiosis, and Oxidative Stress

Another factor that has been scientifically shown to induce and increase free radicals and oxidative stress is dysbiosis. Dysbiosis is described as an unbalanced gut microbiota and there are three types:

  1. Loss of beneficial bacteria
  2. Overgrowth of potential pathogens
  3. Reduction or loss of bacterial diversity

In most cases, the different types of dysbiosis occur at the same time[xi] and it’s connected to a wide range of diseases, including inflammatory bowel disease (IBD).

IBD is a chronic inflammatory disease that affects the intestines and includes conditions like ulcerative colitis and Crohn’s Disease. Although the exact cause of IBD is still debated, research shows there is a link between the gut microbiota, oxidative stress, and the body’s immune response. Generally, the development of IBD occurs alongside persistent oxidative stress and a chronic inflammatory response caused by an imbalanced gut microbiome[xii].

The pathogenic mechanisms of IBD include external or environmental factors such as a high-fat diet, smoking, and disrupted circadian rhythms (think night shift workers and medication). All these factors can result in oxidative stress, promoting dysbiosis, which in turn causes damage to the intestinal barrier and ignites an inflammatory response.

But these mechanisms are also linked to other dysbiosis-associated diseases, including:

  • Obesity
  • Type 2 diabetes
  • Neurodegeneration
  • Cancer

For example, evidence suggests that the increase in oxidative stress, induced by dysbiosis in the gut, can lead to the development of Alzheimer’s Disease[xiii]. Importantly, this highlights that inflammation and the increase in oxidants in the gut can have far-reaching effects around the body.

Can I Stop Dysbiosis?

Dysbiosis, in effect, can be prevented and potentially reversed, but to achieve this the gut needs to be reset so that it can rebalance. Several therapeutic interventions may help to re-establish gut homeostasis. The most common are:

  • Probiotics
  • Prebiotics
  • Synbiotics[xiv]

Diet and the gut microbiome

Perhaps the biggest influence on the balance of the gut microbiota is diet. As we’ve previously seen, the food we eat can disrupt the balance of the ecosystem, particularly foods that are high in fat.

The typical Western Diet, which is rich in meat, sugar, and saturated fat, puts the body at greater risk of dysbiosis and oxidative stress. These foods result in compositional changes, with the Western Diet associated with a higher Firmicutes/Bacteroidesratio, this is also true for the microbiomes of obese individuals[xv].

But just as diet can harm the gut microbiome, it can also have a positive effect. Don’t forget, many of the natural foods available contain natural antioxidants that can pair up with the free radicals zooming around your body and lower the inflammatory response, and in turn oxidative stress.

Try our Prevention and Repair Recipes for a powerful antioxidant punch using our Apple Peel Powder.

Probiotics, prebiotics and synbiotics

Probiotics, prebiotics and synbiotics have all been shown to promote good gut health, and their positive impacts through modulating the microbiome can alleviate or reduce oxidative stress.

For example, both prebiotics and probiotics can manipulate the composition of the gut microbiome, leading to the increased production of metabolites such as SCFAs which are known to reduce oxidative stress by regulating the body’s immune response[xvi].  Research has shown that probiotics like Bifidobacterium bifidum, B. lactis, Lactobacillus plantarumand L. salivariushave high free radical scavenging activities[xvii].

Therefore, it is important to incorporate prebiotic and fermented foods into your diet, to reap their antioxidant benefits.


It has been demonstrated that human milk oligosaccharides have antioxidant properties. In an animal study by Wang et al. (2022), it was found that the HMO, 2’-Fucosyllactose (2’-FL) lowered the incidence of oxidative stress in elderly mice and improved the gut barrier function and the production of short-chain fatty acids[xviii].

Human milk oligosaccharides have a wide range of benefits for human health, both for infants and adults. Primarily, they are prebiotics that help to nourish the good gut bacteria, but this nourishment sparks a cascade of advantages for the human body, including a strengthened intestinal barrier, heightened immunity, and neuroprotective effects.


Your body is a temple. A temple that needs protecting if you want it to protect you, it is a two-way street. Natural functions of the body initiate oxidant production. The harmful activities of oxidants can be limited under optimum circumstances. You can lower the incidence of oxidative stress in your body by eating the right diet and reducing your exposure to other harmful environmental factors, like tobacco smoke.

Written byLeanne Edermaniger, M.Sc. Leanne is a professional science writer who specializes in human health and enjoys writing about all things related to the gut microbiome.  


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[ii] Nolfi-Donegan D, Braganza A, Shiva S. Mitochondrial electron transport chain: Oxidative phosphorylation, oxidant production, and methods of measurement. Redox Biol. 2020 Oct;37:101674. doi: 10.1016/j.redox.2020.101674. Epub 2020 Aug 6. PMID: 32811789; PMCID: PMC7767752.

[iii] Maltepe, E., Saugstad, O. Oxygen in Health and Disease: Regulation of Oxygen Homeostasis-Clinical Implications. Pediatr Res 65, 261–268 (2009).

[iv] Ray PD, Huang BW, Tsuji Y. Reactive oxygen species (ROS) homeostasis and redox regulation in cellular signaling. Cell Signal. 2012 May;24(5):981-90. doi: 10.1016/j.cellsig.2012.01.008. Epub 2012 Jan 20. PMID: 22286106; PMCID: PMC3454471.

[v] Pham-Huy LA, He H, Pham-Huy C. Free radicals, antioxidants in disease and health. Int J Biomed Sci. 2008 Jun;4(2):89-96. PMID: 23675073; PMCID: PMC3614697.

[vi] Lobo V, Patil A, Phatak A, Chandra N. Free radicals, antioxidants and functional foods: Impact on human health. Pharmacogn Rev. 2010 Jul;4(8):118-26. doi: 10.4103/0973-7847.70902. PMID: 22228951; PMCID: PMC3249911.

[vii] Ahmad, R. (2018). Introductory Chapter: Basics of Free Radicals and Antioxidants. InTech. doi: 10.5772/intechopen.76689

[viii] Antioxidants [Internet]. 2021 [cited 2024 Jan 10]. Available from:

[ix] Drews G, Krippeit-Drews P, Düfer M. Oxidative stress and beta-cell dysfunction. Pflugers Arch. 2010 Sep;460(4):703-18. doi: 10.1007/s00424-010-0862-9. Epub 2010 Jul 23. PMID: 20652307.

[x] Schieber M, Chandel NS. ROS function in redox signaling and oxidative stress. Curr Biol. 2014 May 19;24(10):R453-62. doi: 10.1016/j.cub.2014.03.034. PMID: 24845678; PMCID: PMC4055301.

[xi] DeGruttola AK, Low D, Mizoguchi A, Mizoguchi E. Current Understanding of Dysbiosis in Disease in Human and Animal Models. Inflamm Bowel Dis. 2016 May;22(5):1137-50. doi: 10.1097/MIB.0000000000000750. PMID: 27070911; PMCID: PMC4838534.

[xii] Li L, Peng P, Ding N, Jia W, Huang C, Tang Y. Oxidative Stress, Inflammation, Gut Dysbiosis: What Can Polyphenols Do in Inflammatory Bowel Disease? Antioxidants (Basel). 2023 Apr 20;12(4):967. doi: 10.3390/antiox12040967. PMID: 37107341; PMCID: PMC10135842.

[xiii] Das TK, Ganesh BP. Interlink between the gut microbiota and inflammation in the context of oxidative stress in Alzheimer's disease progression. Gut Microbes. 2023 Jan-Dec;15(1):2206504. doi: 10.1080/19490976.2023.2206504. PMID: 37127846; PMCID: PMC10153019.

[xiv] Gagliardi A, Totino V, Cacciotti F, Iebba V, Neroni B, Bonfiglio G, Trancassini M, Passariello C, Pantanella F, Schippa S. Rebuilding the Gut Microbiota Ecosystem. Int J Environ Res Public Health. 2018 Aug 7;15(8):1679. doi: 10.3390/ijerph15081679. PMID: 30087270; PMCID: PMC6121872.

[xv] Brown K, DeCoffe D, Molcan E, Gibson DL. Diet-induced dysbiosis of the intestinal microbiota and the effects on immunity and disease. Nutrients. 2012 Aug;4(8):1095-119. doi: 10.3390/nu4081095. Epub 2012 Aug 21. Erratum in: Nutrients. 2012 Oct;4(11)1552-3. PMID: 23016134; PMCID: PMC3448089.

[xvi] Huang W, Guo HL, Deng X, Zhu TT, Xiong JF, Xu YH, Xu Y. Short-Chain Fatty Acids Inhibit Oxidative Stress and Inflammation in Mesangial Cells Induced by High Glucose and Lipopolysaccharide. Exp Clin Endocrinol Diabetes. 2017 Feb;125(2):98-105. doi: 10.1055/s-0042-121493. Epub 2017 Jan 3. PMID: 28049222.

[xvii] Kang, CH., Kim, JS., Park, H.M. et al. Antioxidant activity and short-chain fatty acid production of lactic acid bacteria isolated from Korean individuals and fermented foods. 3 Biotech 11, 217 (2021).

[xviii] Wang J, Hu JQ, Song YJ, Yin J, Wang YY, Peng B, Zhang BW, Liu JM, Dong L, Wang S. 2'-Fucosyllactose Ameliorates Oxidative Stress Damage in d-Galactose-Induced Aging Mice by Regulating Gut Microbiota and AMPK/SIRT1/FOXO1 Pathway. Foods. 2022 Jan 7;11(2):151. doi: 10.3390/foods11020151. PMID: 35053883; PMCID: PMC8774504.

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