Vegetarian Diet, Glutathione and Oxidative Stress

A reader sent me a link to the following article, Back-Loading Interview w Kiefer, Part III. Upon doing some checking, it turns out that “Kiefer” is the mastermind behind a weight-loss and bodybuilding program he calls Carb Backloading. For $57 you can download his PDF on carb backloading and learn all about it (something I have not done). What I’ve gleaned about the program is that Kiefer says that the body’s circadium rhythms are such that if you eat carbohydrates in the early part of the day, they will be stored as fat. But if you do a hard workout and then eat carbohydrates later in the day, they will be stored as glycogen to prime you for your next workout.

I don’t know if there is any truth to this – it’s certainly not something the American College of Sports Medicine has endorsed at this time and I, for one, eat carbohydrates (and fat and protein) in the mornings and have been fairly successful at keeping off the body fat.

But this isn’t why I’m writing this post.

The reader who sent me the link was mostly concerned about what Kiefer had to say about the antioxidant potential of a vegetarian diet. From his interview with Sean Hyson:

Sean: Here’s something else I was blown away by when I read it, the idea that whey protein might be a better antioxidant than fruits and vegetables. You say that it works “by increasing levels of an amino acid called glutathione, which fuels the main antioxidant machinery of the cells in the body. Eating fruits and vegetables pales in comparison to the glutathione mechanism. Glutathione also helps recycle other antioxidants like Vitamin C and Vitamin E, decreasing the need to use vitamins. …”

Kiefer: …When you look at the research, some of the most compelling research was done with vegetarians….vegetarians literally have 10,000 times the concentration of antioxidants in their systems, but they have the same rate of all cancers….So for all that extra antioxidant machinery that vegetarians supposedly have, it offers no extra protection.

Oh, no you didn’t, Mr. Kiefer!

When I read the study from my last post, Near Vegan Diet Improves Type 2 Diabetes (1), I couldn’t help but notice that the researchers measured the glutathione levels in the subjects and found that the vegetarian diet actually increased reduced glutathione (as distinct from oxidized glutathione) during both the non-exercise and exercise phases, while the reduced glutathione levels in the control group went down in both phases of the study.

My understanding is that you want higher levels of reduced glutathione as that is the version that can do it’s free radical scavenging.

Three enzymes also were measured in the study: glutathione reductase, glutathione peroxidase, and glutathione transferase. My sense is that you want these enzymes to be low as they indicate oxidative activity, but this is not clear to me – if you are living a lifestyle with a lot of oxidative stress, then these enzymes being high would indicate that glutathione is doing its job.

The enzyme levels changed between the diet groups, but there was no clear direction (they were all over the map for both diet groups during both phases). See the postscript for the changes in these enzymes.

Based on this study, it would seem that a vegetarian diet does have ample glutathione potential. But it’s just one study, so I looked further and came across another one I will post about tomorrow. And there might be more after that. Stay tuned.

You can support by purchasing anything through these links

Vegan for Life: Everything You Need to Know to Be Healthy and Fit on a Plant-Based Diet from


1. Kahleova H, Matoulek M, Malinska H, Oliyarnik O, Kazdova L, Neskudla T, Skoch A, Hajek M, Hill M, Kahle M, Pelikanova T. Vegetarian diet improves insulin resistance and oxidative stress markers more than conventional diet in subjects with Type 2 diabetes. Diabet Med. 2011 May;28(5):549-59. | Link


Below are the enzymes followed by the diet group and the changes in the enzymes during the non-exercise and exercise phases of the study:

Glutathione reductase:
vegetarian – decreased, decreased
control – decreased, increased

Glutathione peroxidase:
vegetarian – increased, stabilized
control – decreased, increased much higher than vegetarian

Glutathione transferase:
vegetarian – increased, stabilized
control – increased, stabilized

6 Responses to “Vegetarian Diet, Glutathione and Oxidative Stress”

  1. Rob m Says:

    > vegetarians literally have 10,000 times the concentration of antioxidants in their systems

    Is this true? It sounds like such an awesome stat so it’s hard for me to believe. I’m not saying it’s good or bad, it just sounds like an exaggeration: ‘yeah man like a million times!!!1 LITERALLY!’

  2. Bertrand Russell Says:

    Jack, it might be useful to explain that you mean “reduced” in the chemical sense (e.g., reduction as the opposite of oxidized), as opposed to “less”. I.e., “reduced glutathione” is a certain form of glutathione. Your other readers are probably smarter than I am, but when I read “increased reduced glutathione” for the first time, my B12-deprived brain kinda imploded.

    And I’m still kinda confused. (OK, not kinda) Which of the three enzymes is supposed to be good? From the language, it would seem like you want more reductase (parallel to reduced?), and lower peroxidase (oxidizer), but could it be the opposite?

  3. Jack Norris RD Says:

    Rob m,

    It’s possible that at least one study showed that, but it sounds high to me. I have never made a point of quantifying the research on antioxidant status of vegetarians, but I am in the process of reviewing it so stay tuned.

  4. Jack Norris RD Says:


    I added a parenthetical note above to explain it. I had put “reduced glutathione” in italics to try to set it off from the “increased” part, but now that you mention it, that is funny: increased reduced glutathione.

    As for the enzymes, I couldn’t figure it out. It seems to me that they would be high if antioxidant needs are high which could be a result of diet or of exercise (or some other stressor). But if you don’t have enough glutathione, then perhaps the body would have no need to produce the enzymes. I have a lot of questions about it.

  5. pedalare Says:

    Glutathione is an extremely interesting and powerful antioxidant and plays a number of roles in the cell. among these are…

    1.The antioxidant ability of glutathione lies entirely in the activity of glutathione peroxidase. This primarily removes hydrogen peroxide, or lipid peroxides, from the cell, producing water. If hydrogen peroxide wasnt removed, it will readily form the hydroxy radical which is one of the most damaging free radicals produced and readily attacks lipids in membrane layers. Once lipid peroxidation has been initiated it is upto lipid soluble antioxidants like vitamin E to break the destructive chain.

    2. Lipid peroxidation can result in the release of several cytotoxic oxidation by products… This is where glutathione plays another role, in detoxification. In the reduced state, glutathione is a sulfhydrl with a readily available hydrogen. It is able to conjugate with toxins eliminating their toxicity while depleting total glutathione. this reaction is catalyzed by the enzyme glutathione transferase. This activity is a good indictaor of total oxidative stress in the cell.

    3. Glutathione can also donate its hydrogen to oxidized form of vitamin C to produced the reduced form, which can then reduce vitamin E… if you can now see the cycle… going back to vitamin E and lipid peroxidation! In this reaction glutathione is in the inactive oxidizes form, but through the reaction catalyzed by glutathione reductase it can easily take a hydrogen from NADPH to continue the cycle again.

    Now i few points… the main form of glutathione peroxidase is a selenium containing enzyme, and although not confirmed this is where the apparent antioxidant ability of selenium lies (increasing selenium in the diet does not increase glutathione peroxidase activity).

    I would suggest that if the activity of glutathione transferase is high then it is likely that the body is under oxidative stress, and your glutathione levels will deplete, leading to a general increased expression of glutathione in the cells. this will also be accompanied by increases in enzyme activities. because glutathione is involved in so many of the steps of the antioxidant cascade, you can imagine that this system is turning over at a 100 miles an hour under oxidative stress. Luckily the body can produce glutathione, unlike vitamin E and C which is essential in the diet.

    I hope that gives you a better insight into the world of glutathione as an antioxidant, and is not too confusing.

  6. Jack Norris RD Says:


    Thanks so much for that explanation. If you (or other readers) didn’t see it, you might be interested in my post on selenium here:

Leave a Reply