In my continuing review of the literature of the glutathione and antioxidant status of vegetarians, today’s episode is a 2007 cross-sectional study from Ireland (1).
The study included 31 vegetarians (including 6 vegans) and 58 omnivores. The results were adjusted for age, gender, and body mass index (which did not significantly differ between the two groups). Antioxidant supplements were allowed and results were examined both for the entire group and for non-supplement users.
There were no significant differences between the groups for glutathione or any antioxidant enzymes. The only differences between the two groups of note were:
• Vegetarians had higher levels of carotenoids, associated with a higher vegetable intake.
• Among those not taking antioxidant supplements, the omnivores had a higher total antioxidant status (known as FRAP). This was due to higher uric acid levels (which is an antioxidant) in the omnivores, which was probably due to meat intake.
The authors say, “The results of this study indicate that there were no differences between vegetarians and omnivores in the level of cellular endogenous antioxidants…and in the plasma levels [of] antioxidant nutrients (vitamin C, retinol and a-tocopherol) despite the increased dietary intakes of these antioxidants by the vegetarian group. The reason for the lack of difference in the antioxidant vitamin status between the two groups might partly be due to homeostasis…” In other words, once you have reached a certain threshold of antioxidants in your system, adding more might not do much.
Regarding the uric acid and total antioxidant capacity, this study was interesting, and could possibly indicate that lacto-ovo vegetarians are at a disadvantage. As we saw from my recent post Higher Uric Acid Levels in Vegans, vegans would not be at a disadvantage.
In terms of glutathione levels, we now have a cross-sectional study (1) and a clinical trial (2) indicating that vegetarians have similar glutathione levels as omnivores.
As an aside, one other measure of interest was that plasma zinc levels did not differ between the two groups.
In continuing my glutathione investigation (see my two posts from last week Vegetarian Diet, Glutathione and Oxidative Stress and Oxidative Stress in Vegetarian Diets: Take Two), I came across a study of selenium status of German vegetarians from 2010 that I had not previously posted about (1).
The reason this is relevant to glutathione is that in assessing selenium status, the researchers measured a protein that requires selenium, mentioned in the earlier posts, glutathione peroxidase.
Selenium is considered an antioxidant because it is needed for the production of glutathione peroxidase which, in turn, neutralizes reactive oxygens species by “coupling their reduction with the oxidation of glutathione (2).”
Because animals require selenium to live, non-vegans should be able to get selenium from animal products. Plants can absorb selenium from the soil, but it has to be in the soil. The US soil typically has decent levels of selenium, but the German soil is low in selenium.
The study found that vegetarians had only 71% of the selenium storage protein, selenoprotein P (SEPP), as did the meat-eaters. However, they had the same levels of glutathione peroxidase. When the vegans were separated from the lacto-ovo vegetarians, it did not change the findings for either group.
The authors state, “Whether the differences in SEPP or total serum Se concentrations are important for health issues and disease risk or for the course of pathologies remains to be demonstrated.”
However, this study, as the previous two I blogged about, provides some evidence that the glutathione status, via glutathione peroxidase levels, of vegetarians is similar to meat-eaters.
Kiefer, you are now 0 for 3. To quote Yogi Berra, “It’s getting late early.” As a Sacramento Kings fan, I can identify.
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.
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:
vegetarian – decreased, decreased
control – decreased, increased
vegetarian – increased, stabilized
control – decreased, increased much higher than vegetarian
vegetarian – increased, stabilized
control – increased, stabilized