Do Plant Antioxidants Work as Antioxidants in Humans?
I frequently see articles, comments, posts, and various “scientific” claims about antioxidants in plants. We are told to eat plants, some more than others, for their antioxidants. We are told that these antioxidants are healthy and function as antioxidants in our body. But is there any truth to this? Let’s look into this deeper.
What is an Antioxidant?
An antioxidant is a “chemical” that is able to reduce oxidative damage caused by oxygen (reactive oxygen species, or ROS). Most metabolic processes require oxygen, some more than others, and in the process of metabolic functions, lots of oxidative damage can collect. Antioxidants grab the oxygen (free radical) and deactivate it.
Do humans need antioxidants?
Many human processes cause oxidative stress by reactive oxygen species, and so antioxidants are essential for health and survival. We use antioxidants in processes, such as ATP production, aging, certain diseases like cancer, and neurodegenerative diseases, like Alzheimer’s, and we also use antioxidants in cell signaling and immune system responses to attacks (infections), such as from viruses and bacteria.
Do plant antioxidants work in our body as antioxidants?
No they don’t. They can’t. Antioxidants are very specific to the “creature” that creates them because the properties of the antioxidants fit the oxidative damage type to be reduced. A plant has different metabolic processes from a human and so what is an antioxidant for a plant cannot be a REDOX function in a human.
The key human antioxidants are glutathione (GSH) and superoxide dismutase (SOD), generated by our own body, as needed!
Categories of Major Human Antioxidants
GSH: The main antioxidant that neutralizes ROS and recycles vitamin C & E.
SOD: Converts superoxide radicals (O₂•⁻) into hydrogen peroxide (H₂O₂), which is further neutralized by catalase or glutathione peroxidase.
Categories of Plant Antioxidants
| Type | Examples | Functions in Plants |
|---|---|---|
| Enzymatic Antioxidants | Superoxide Dismutase (SOD), Catalase (CAT), Glutathione Peroxidase (GPX), Ascorbate Peroxidase (APX) | Convert ROS (O₂•⁻, H₂O₂) into less toxic forms to prevent oxidative damage |
| Non-Enzymatic Antioxidants | Vitamin C, Vitamin E, Glutathione, Carotenoids | Scavenge ROS and protect cell membranes |
| Polyphenols & Flavonoids | Quercetin, Kaempferol, Catechins, Anthocyanins | Protect against UV radiation, pests, and oxidative stress |
| Carotenoids | Beta-Carotene, Lutein, Lycopene, Astaxanthin | Protect chlorophyll from oxidative damage, dissipate excess light energy |
| Alkaloids | Caffeine, Theobromine, Curcumin | Defense against herbivores, microbial infections, and oxidative damage |
| Sulfur-Containing Antioxidants | Sulforaphane, Allicin, Glucosinolates | Detoxify pollutants, regulate plant immune responses |
Key Differences Between Human and Plant Redox Systems
| Feature | Humans (Animals) 🧬 | Plants 🌱 |
|---|---|---|
| Main Energy Source | Oxidative phosphorylation (O₂-dependent ATP production in mitochondria) | Photosynthesis (light-driven ATP and NADPH production in chloroplasts) |
| Primary Redox Function | Regulate cellular metabolism & prevent oxidative damage | Protect against UV light, drought, pathogens, and oxidative stress from photosynthesis |
| Key Antioxidants | Glutathione (GSH), superoxide dismutase (SOD), catalase, vitamin C, vitamin E, uric acid | Flavonoids, polyphenols, carotenoids, ascorbic acid (vitamin C), glutathione, SOD, peroxidases |
| Primary Reactive Oxygen Species (ROS) Sources | Mitochondria (electron transport chain, ETC), peroxisomes, NADPH oxidases | Chloroplasts (photosystem I & II), peroxisomes, mitochondria |
| Major Redox Signaling Pathways | Nrf2-Keap1 (antioxidant response), AMPK (energy sensing), Sirtuins (aging & stress response) | NPR1 (redox signaling for immune defense), MYB (flavonoid synthesis), RBOH (ROS burst for stress adaptation) |
| Oxidative Stress Sensitivity | ROS must be tightly controlled to avoid cellular damage & disease (e.g., cancer, neurodegeneration) | Plants intentionally generate ROS for stress signaling & adaptation |
How Do Plant Antioxidants Work in the Human Body?
Plant antioxidants (polyphenols, flavonoids, carotenoids, etc.) rarely act as antioxidants, because:
- They are poorly absorbed in their original form.
- They are extensively metabolized in the liver and gut.
- They often act as pro-oxidants first, triggering the body’s own antioxidant defenses.
Instead of acting directly like human antioxidants (e.g., glutathione, SOD, catalase, uric acid, vitamin C, vitamin E), plant antioxidants stimulate the body’s endogenous defense systems through hormesis.
Hormesis
Hormesis is a phenomenon in biology where a low dose of a substance or stressor that would normally be harmful in larger doses can have beneficial effects in smaller doses. It is based on the principle that moderate stress can trigger adaptive responses that improve resilience and health. A good hormesis mediator example is a vaccine. A vaccine is a low dose viral particle, an irritant, which initiates the immune response to that virus.
Plant vs Human Antioxidants
1️⃣ Polyphenols & Flavonoids (Quercetin, Resveratrol, EGCG, etc.)
- Plants: Protect against UV damage, insects, and oxidation.
- Humans: Do not directly neutralize free radicals but activate antioxidant genes (Nrf2 pathway).
🔬 Mechanism:
- Flavonoids trigger Nrf2 activation, increasing the body’s natural antioxidant enzymes:
- Glutathione peroxidase
- Superoxide dismutase (SOD)
- Catalase
2️⃣ Carotenoids (Beta-Carotene, Lycopene, Lutein, Astaxanthin)
- Plants: Absorb light and neutralize singlet oxygen.
- Humans: Act as pro-vitamin A (retinoids) and modulate oxidative stress in specific tissues.
🔬 Mechanism:
- Carotenoids protect lipid membranes from peroxidation.
- Beta-carotene converts to vitamin A, but high doses can be pro-oxidant in smokers.
3️⃣ Tannins & Proanthocyanidins (From Tea, Berries, Cocoa, Wine)
- Plants: Act as antimicrobial agents and UV protectors.
- Humans: Alter gut microbiota, improve endothelial function, and reduce inflammation.
🔬 Mechanism:
- Tannins improve nitric oxide (NO) production, reducing oxidative stress in blood vessels.
- Modulate gut bacteria, which then produce metabolites with antioxidant properties.
4️⃣ Sulfur Compounds (Glucosinolates, Allicin)
- Plants: Protect against insects and pathogens.
- Humans: Enhance detoxification (phase II liver enzymes) and reduce oxidative stress indirectly.
🔬 Mechanism:
- Sulforaphane (from broccoli) induces Nrf2 and glutathione production.
- Allicin (from garlic) boosts hydrogen sulfide (H₂S), which reduces oxidative stress.
In Summary:
Plant antioxidants do not replace of function as human antioxidants but initiate human antioxidant response by hormesis. However, using plants for this function all the time causes an overacting immune response, which we refer to as autoimmune diseases. So… it follows.. if you have autoimmune diseases: stop eating plants!
Comments are welcome, as always, and are moderated for appropriateness.
Angela
Stanton Migraine Protocol 