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Mitochondrial Theory of Aging

The role of the detoxifying enzyme superoxide dismutase in staving off aging, cancer, and dementia and what we can do to boost its activity.

December 28, 2010 |
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Supplementary Info

Sources Cited



Let me end with one final topic. In 2010 we earned a lot more about aging and eating. Awarded the highest honor for scientific achievement in this country, one of the greatest biochemists of all time wrote that, “Aging is a disease. The human lifespan simply reflects the level of free radical damage that accumulates in cells. When enough damage accumulates, cells can’t survive properly anymore and they just simply give up.”
First proposed in 1972, the Mitochondrial Theory of Aging suggests that it’s free radical damage to our cells’ powersource, known as mitochondria, that lead to a loss of cellular energy and function over time. It’s a little like charging your ipod battery over and over again; every time the capacity gets less, and less. Mitochondria are like miniature blast furnaces inside our cells where the food that we eat… is converted, into useable energy.
In my Stopping Cancer Before it Starts DVD, I go into detail about the, quantum biology of oxidative phosphorylation, but just to simplify, it is in these fireworks inside the mitochondria, where the oxygen we breathe may get a hold of an electron we ate that was pumped with energy by plants (thanks to photosynthesis) and transform that oxygen molecule into what’s called superoxide, which can damage our delicate cellular machinery—oxidize our cellular machinery. Basically we're rusting—that's what rust is, right? The oxidation of metal. And scientifically, aging has been considered the slow oxidation of our bodies. Like those brown age spots on the back of people’s hands? That's just oxidized fat under the skin. Oxidant stress is why we get wrinkles, that's why we lose some of our memory, that's why our organ systems break down as we get older.
How do we slow down oxidation? By eating foods containing anti-oxidants. If you want to know if a food has a lot of antioxidants in it you slice it open, expose it to air—expose it to oxygen and see what happens. Does it oxidize, does it turn brown? Think about our two most popular fruits: apples and bananas. Turn brown right away—not a lot of antioxidants inside there. How to do you keep your fruit salad from turning brown though? Add lemon juice, which has vitamin C in it, an antioxidant, which can keep your food from oxidizing and can do the same thing inside our bodies.
Here’s the catch, though: Many antioxidants can’t penetrate through the mitochondrial membrane into the mitochondria. So they can protect the rest of the cell, protect our DNA, but they can’t get access inside the powerplants of our cells and so may be helpless to slow down the aging process. That’s why our bodies, have an enzyme called superoxide dismutase. It’s a detoxifying enzyme within our mitochondria that neutralizes superoxide, and turns it back into oxygen.
Because of it’s “bomb-defusing” role, it’s considered a tumor suppressor gene staving off cancer, considered neuroprotective in our brain, staving off dementia. In fact the reason women live longer than men, may be because they have superior enzymatic activity of this superoxide dismutase.
This Mitochondrial Theory of Aging has enjoyed such universal acceptance within the scientific community, that there was even a paper published last year asking whether there was anything more to aging at all?
OK, bottomline: how do we boost the activity of this anti-aging, anti-cancer, anti-Alzheimers enzyme? Become a woman. Or become a vegetarian. Last year researchers compared this enzyme’s activity in omnivores versus vegetarians. This is your superoxide dismutase enzyme activity if you’re over 85. When you’re younger, this enzyme may work a little better, but when one eats vegetarian it works a lot better.
Eating vegetarian appears to boost this anti-aging enzyme’s activity 300%! A three-fold increase in the expression of the superoxide dismutase gene in the vegetarian group compared to the omnivore control group. We had no idea. No wonder vegetarians live longer; no wonder they have less cancer and cardiovascular disease—we had just never tested them for this enzyme before.
A higher enzyme expression, at the genetic level. Thus, a better defense against superoxide radicals might be expected as a consequence of a vegetarian diet. So maybe that’s why lower rates of cancer and chronic cardiovascular disease compared to omnivores. Yes, they eat more phytonutrients, but the higher protection against chronic disease in vegetarians may also be explained by what are called epigenetic changes. You think you’re just born with genes and stuck with them? No, we now know that what we eat can turn on and off gene expression. And in this case, eating vegetarian seems to significantly boost the activity of one of the most important workhorse enzymes in the body.


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Dr. Michael Greger

Doctor's Note

Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on aging. Also, there are 1,686 other subjects covered in the rest of my videos--please feel free to explore them as well!

Also, check out my associated blog posts for some more context: Acai to Zucchini: antioxidant food rankingsKiwi Fruit for Irritable Bowel SyndromeEating Green to Prevent Cancer, Ergothioneine: A New Vitamin?, and Hibiscus Tea: The Best Beverage?


  • Michael Greger M.D.


  • Robert Edmands

    Intriguing! I know of mitochondria as the organs of respiration in the cell. They are thought to have been captured in the early days of evolution like chloroplasts were in plants. They are alien. They don’t have the same number of chromosomes as human cells. Rusting out.
    Amazing analogy. Linus Pauling was fanatic about vitamin C. That didn’t turn out to be the cure all.

    Becoming a woman is not an option for me. This despite the increasing acceptance of transgendered individuals.

    Hormones and psychology have branded me with a distinctive phenotype. The river doesn’t go upstream! I’ll try improving my diet instead!

  • Lance Strish

    What do you make of this statement?
    DrEades had a post on this quoting Aubrey de Grey’s Ending Aging
    ‘Chapter 5, Meltdown of the Cellular Power Plants’-
    DrEades adds:
    ‘But what if all this increased antioxidant activity is because the diet is so inflammatory (as the section in de Grey’s book would have us believe is the case with low-carb diets)? That’s where the CAT and SOD measurements come into the picture. CAT and SOD are catalase and super oxide dismutase, both enzymes involved in the body’s defense against increased oxidation. If CAT and SOD are not elevated, that indicates that the body isn’t threatened with increased oxidative stress. MDA is the malondialdehyde levels, which were unchanged. MDA is another marker for oxidative stress. The fact that it’s unchanged also is just another indicator that the diet didn’t increase oxidative stress.’”

    • mehitabel

      You’re right. Thank your for bringing Eades. The video is wrong about vegetarian diet being good because it increases SOD. It increases SOD because it’s inflammatory and SOD is being upregulated because of the carb ingestion. It’s totally unnatural to our evolutionary diet. And when the video ascribes long life and less disease to vegetarianism it couldn’t be more wrong.
      “Similarly, the Russians of the Caucasus mountains live to great ages on a diet of fatty pork and whole raw milk products. The Hunzas, also known for their robust health and longevity, eat substantial portions of goat’s milk which has a higher saturated fat content than cow’s milk. In contrast, the largely vegetarian Hindus of southern India have the shortest life-spans in the world, partly because of a lack of food, but also because of a distinct lack of animal protein in their diets. H. Leon Abrams’ comments are instructive here:


      Many, many vegetarians come back to an omnivore after decades of ruining their health. This video is really an indictment of vegetarianism…the body is saying no, no, no by the increased SOD production and when it’s not enough and the inflammation is daily for years vegetarians get cancer. I’ve seen bright people pick the wrong paradigm.

      • Toxins

        This video is not opinionated in any way, its simply laying out the facts based on the studies. You can view the sources cited yourself. Furthermore, a plant based diet is NOT pro inflammatory, quite the opposite in fact.

        In addition, degenerative diseases like heart disease, cancer, diabetes, and auto immune diseases are reversible on a plant based diet, even one that is complex carbohydrate centered, not a meat centered diet.

        The assumption that vegans also lack protein is complete nonsense, 99.9% of all whole plants are complete proteins and energy expenditures satisfy protein needs. Our protein needs are also very low, it has been said by Dr. William Rose that our minimum protein requirements are 20 grams per day.

        I am not going to argue what we were “evolutionary” brought up to eat because your arguing a carnivorous diet “an observation contradicted by all aspects of our anatomy and physiology. Our teeth are not like a cat’s, we have no claws for tearing apart meat, our intestine is designed for digesting plant foods, not meat, and our livers have a limited capacity to metabolize cholesterol, which is one big reason our cholesterol levels rise on the Western diet.”

        Its about what we know now, not how we “think” we were brought up in the past. For example, cooking food is unnatural, yet it is simply pre digestion and actually allows the bioavailability of many nutrients to be absorbed.

        • mehitabel

          “Few favorable associations between fruit and vegetable intake and biomarkers for chronic disease risk in American adults”

          “After adjusting for demographic factors, socioeconomic factors, lifestyle factors, body mass index, total energy intake, and the presence of at least 1 of our 5 predetermined comorbidities, no associations of reduced or increased risk were observed in any quartiles of combined fruit and vegetable intake.”


          with respect you cannot win arguing against evolution. Our eyes face forward because we are predators, not prey. Prey animals have eyes on the side of their head — they are plant eaters. Our stomachs are not evolved to eat plants, like a cow or a horse — that’s silly lack of understanding. The nutritient density of meat, and ONLY the nutrient density of meat, allowed us to spare the energy required to evolve a massive stomach for plant digestion (apes) and divert that energy into brain development.

          In terms of generations, we been eating a predominately meat based diet for 100,000 generations. Agriculture, and it’s contributions of slowly increasing quantity of carbs in our diet, started only 500 generations ago. Here’s the kicker — our current massive, massive, rapid increase of produce only started with the Industrial Revolution — 13 generations ago — coincidental with massive disease.

          You state “99.9% of all whole plants are complete proteins.” Plants are carbohydrate. But even your guy McDougall gets it wrong.


          “The kindest thing I can say about McDougall is that he is a ranting extremist. He is stuck in his vegan rut and doesn’t seem to understand how metabolism works.

          The weird thing is that I believe he gets results! How come?

          A real low fat diet will dump almost all PUFA. A real Food diet will eliminate all sugar. A hypocaloric weight reduction diet will both reduce insulin levels (a growth promoter for breast cancer) and switch metabolism to animal sourced saturated fat, the best source of calories available. Of course ketosis is out of the question, low fat veganism is a very limited approach.

          Does McDougall know what he’s doing, to get whatever results he does get?

          No way.

          Petro Dobromylskyj
          This kind of argument is futile because we will never convince the other — and you are welcome to have the last word.
          My last word is “you can choose to eat AS a vegan, but your body will never BE vegan.

          good health,

          • mehitabel

            Petro Dobromylskyj — i love this guy.

            “Eating willow bark is no different from taking aspirin, except it’s slightly more toxic as the salicylic acid, a plant toxin, is not had it’s toxicity reduced (though far from eliminated) by chemical acetylation to give aspirin.






          • Toxins


            This is why we have a liver

          • Toxins

            To say fruits and vegetables are not beneficial is nonsense. Dr. McDougall gets results. He has reversed people’s cancer, diabetes, heart disease, autoimmune disease etc. with this diet so your making a very silly statement to say the diet is flawed…apparently not.

            And yes, all plant foods contain complete proteins, there are not protein deficient whole foods plant based eaters walking around. I myself am a prolific rock climber and since my dietary changes, my strength increases have been significant along with much faster recoveries, more endurance and stamina,, etc.

            Regarding your anatomy debate:

          • mehitabel


            “I noticed that many vegetarian web sites usually devote a page
            attempting to show, by comparative anatomy, that humans are
            herbivores. The Name Milton R. Mills, MD, came up quite a bit. Here is
            what I found out about the good doctor:

            Milton R. Mills, M.D., a Stanford University-trained physician
            specializing in nutrition, practices in Virginia and volunteers as
            associate director of preventive medicine at the Washington-based
            Physicians Committee for Responsible Medicine. He wrote this column
            for the Knight Ridder/Tribune News Service.

            PCRM! Kinda says it all, doesn’t it?

            Fortunately, not all vegetarians are as brainwashed. Here is what
            vegetarian John McArdle, Ph.D, anatomist and primatologist has to say
            about the taxonomy of humans compared to carnivores and herbivores:”


          • smashchamps77

            mehitabel, after reading through this two year old thread, I can honestly say that you’ve done a terrible job trying to defend your delusive ideas. You claim that Toxins is using biased information, yet ironically you cite a source which has been overused and is probably biased itself! That source has insubstantial evidence; not enough to provide a sound argument on your part. You can argue all you want about how you think humans have evolved as meat-eaters, but for every minor piece of evidence you provide to substantiate your claim, I can produce at least one to contradict it. Our eyes face forward because we’re predators you say? Well, what about the color of our eyes? Predators would have a dark sclera (the part surrounding the pupils) so that prey would not be able to detect the direction of their gaze. This is not the case with humans: our white sclera is quite contrasting to the dark color of our pupils. Our direction of gaze is easily detectable.

            Point being, every single piece of “evidence” you put forth has another piece of evidence that will come to an inverse conclusion. I do believe that our bodies are naturally suited to eat plant foods and know that there are a plethora of findings out there which support this and dispell your previous assertions. Still, I don’t like arguing about evolution, because I understand that even professional archaeologists and anthropologists are constantly contradicting each other and can’t come to a complete consensus.

            What we do know is that, in today’s day and age, a plant-based diet has a multitude of benefits, and humans can thrive off of it. That’s all that should matter.

          • Nekobus

            “Our eyes face forward because we are predators, not prey”. Yes, eyes in the front, just like all other primates. 

          • Lilly

            Gorillas have eyes facing forward. Why aren’t they eating meat?

      • Lilly

        You’re ridiculous. What about Charlotte Gerson? She’s been a vegetarian longer than a decade, she’s in her 80′s and healthy free of disease common to an 80 year old.

      • Joe

        An old post but a point worth making: The Hunza eat mostly plants. They eat lots of fruit and quite a few grains and beans and pulses. Fermented Goats milk + yogurt features, as does a little meat – but by most records they are mostly plant based. As are the Okinawans, the Sardinians and the 7th Day adventists in California (The longest lived group in America.) Researchers consistently find people living in these longevity hotspots are eating mostly plant based. Granted, none are vegan – but the focus is definitely on plants.

        People usually hold the Masai and the Inuit up as examples of animal based success, but their life expectancy is way down compared to previous groups.

        Now I’m not saying this is all proof – there are many other factors such as environmental pollution, social structure and belief systems – but to discard plants as not only worthless but dangerous is to ignore the vast majority of scientific and anecdotal data that exists.

  • Cyclo Uten Etternavn

    Hi Michael,

    This is more of a general question regarding body detoxification:

    What’s your opinion about juice fasting / feasting with fresh fruits and vegetables for the purpose of detoxifying the body?
    Is this method beneficial for getting rid of toxins in your body, or is it just a hype without any scientific evidence?
    Is it even possible to get all the needed nutrients and not actually break down the body during the juice fasting / feasting process?

    • Toxins

      Hello Cylco,
      I believe I can answer your question. People like to throw around the word “cleanse” a lot but it is not always used in the correct sense. It may be due to the fact that you are drinking all liquids so you tend to use the bathroom much more but why not just drink water? Juicing a fruit is no doubt healthy, not harmful. But you throw out 90% of the nutrients when you juice something and its a waste of fruits. It takes 3 oranges to juice a cup of orange juice and its STILL not nutritionally equivalent to 1 plain orange. Not only that, it was shown that if you eat a fat with your nutrient dense foods (such as nuts, seeds, avacados but avoid OIL) then you absorb a significantly greater amount of phytochemicals. Without a fat source you absorb almost no phytochemicals. If your interested in doing a system cleanup, eat a whole foods plant based diet focusing on the most nutrient dense foods you can and drink a lot of water.

  • Donna

    Hi Dr G,

    you made comment to old age spots and oxidised fat under the skin, why does this occur only on the hands, interesting, I have 3, they were there before I went vegan and I have developed no more since that time (11 years) Thanks for a wonderful site with great, relevant and factual information!!

  • DrDons

    The spots tend to occur more on the back of our hands where we get the most sun exposure. Our body is usually working to reverse damage and heal itself. Proper nutrition is important to this healing process. Avoiding excessive sun helps prevent the damage. Since I have been on a plant based diet the age spots have lightened on the back of my hands. Not sure there is a connection but am planning on continuing learning more about the latest in proper nutrition by tuning in to… Be well.

  • wickedchicken

    It’s hard not to feel Invincible listening to all these studies. I think I will live forever ha ha :P

  • Tami Djernes

    This is great, but wouldn’t it be more accurate to use the term “vegan” or “plant-based”?  I grew up “vegetarian”, but what we lacked in meat we made up for by consuming milk, cheese, cottage cheese, sour cream, yogurt, eggs, etc. Vegetarians who consume a lot of dairy and eggs (and processed food) get the same diseases as meat eaters. My mom was a lifelong vegetarian, and she suffered from cognitive decline and dementia the last 14 years of her life.  I’m hoping my unprocessed vegan diet will protect my brain for the rest of my life.  

    • Don Forrester MD

       You make an excellent point there is alot of confusion in the various terms. I come across folks who don’t think fish is a meat and of course the dairy issue as you mentioned. There are many types of vegetarians and new terms are being added like semi-vegetarian or flexitarians all the time. The best terms are the most descriptive… I prefer plant based diet in lieu of vegan and often add the term whole food and maybe mention Vit B12…. so whole food plant based diet with Vitamin B12. FYI… Dr. Neal Barnard has a new book coming out next spring on Dementia which you would probably be interested in. Good luck on your quest to avoid dementia and other chronic diseases. Keep tuned in to as the science just keeps on coming.

  • Valnaples

    What about coenzyme Q10??? Just wondering if anyone takes these supplements? I have been for a while…my dentist does too!

  • Tan Truong

    Wow, this is just amazing.

  • James

    I’m plant based, but intrigued by an increasing amount of stories about great results from certain Paleo-styled diets.. I’m wondering if someone from can comment on this video.. DR. reverses MS with Paleo styled diet:

    • butro78

      Great Video! So glad people are finally taking notice about this stuff. But nothing that can’t be obtained via plants.

      You get so many more toxins from fish and meat than you would get just by eating what animals eat to get their Omegas. NASA actually found that algae based epa/dha was a higher quality and sustainable alternative to traditional fish oils, and uses that for their needs. As far as organ meats for vitamins, minerals, coQ10??? not necessary. And she even talks about only having them once a week. A whole foods, plant-based lifestyle definitely bypasses paleo.

      And I would rather live looking into the future, not like a caveman :)

  • Nutritarian

    What is your opinion of the February 2013 article in Scientific American:
    The Myth About Antioxidants?

    • Nutritarian

      Just received a McDougall Breaking News email that addresses the article:

      • Nutritarian

        Correction, the McDougall Breaking News did not refer to the Scientific American article but an article in my local newspaper…

    • Toxins

      Id be interested in see some studies

  • Alan Heathcote

    Hi Dr G.
    I have just read an article in the Scientific American Feb 2013 page 56 called The Myth of Antioxidants. What do you think of it? Cheers

  • terri

    Questions: what do you think of protocel? what is the best dietary approach for cervical cancer? Thank you!

  • guest

    totally irrelevant sidenote:
    0:52 cutest baby ever. Go vegan babies!
    That is all.