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Response to Mark Sisson’s assertion that vegetables are necessary for health

Mark Sisson is the author of The Primal Blueprint, and the blog Mark’s Daily Apple.
His blog is a great reference, and I like his work.
However, I take exception to the article he posted this week entitled Do You Really Need to Eat Vegetables to Be Healthy?
Although he admits at the end that you probably don’t need them, this admission has much less prominence than the section near the top where he says

“Yes. Yes, you do. Maybe not a huge amount, necessarily. But you do need some.”

Then he goes on to make some arguments for eating vegetables that I’d like to address.

  1. Modern Hunter-Gatherer diets:
    First he argues that three of the four known modern hunter-gatherers that are purported to be carnivorous (Inuit, Masai, and Sami — leaving out Plains Indians) weren’t actually.
    I don’t think that’s really settled, but more importantly it doesn’t matter.
    Even if it were true that all modern primarily carnivorous societies ate some plants, that doesn’t and couldn’t prove we need them.
  2. Plants as medicine:
    A second argument that is weaved throughout the post is that plants have medicinal compounds, and therefore should be eaten.
    But this doesn’t make sense.
    This is an argument for growing plants and extracting compounds so that we can isolate and concentrate medicine into useful portions, while removing the toxins that accompany the source. It’s no argument for taking daily minute doses of medicine along with a bunch of other random stuff that grew with it.
    I’ve addressed that more fully in the post Biochemical Warfare
  3. Missing nutrients:
    Another argument is about getting some particular nutrients.
    It is argued that modern meat may be depleted of some minerals and vitamins that are dependent on the diet of the animal.
    That is, there are wild plants that are part of the diet of wild animals, that they use to make vitamins that we then eat, and modern meat may be inadequate.
    This may well be true, but insofar as it is, it does not make a convincing argument for eating those plants ourselves, along with whatever other matter they contain, any more than it argues for taking supplements.
    Even if modern meat is insufficient, that is no argument for eating vegetables.
    Moreover, a similar argument is sometimes made about plant vitamin and mineral content due to soil depletion, so eating plants may not even solve it.
    (I’m ignoring the part of that section that suggests we only need plants if we refuse to eat offal or reserve the cooking water, since they support the ability to get those nutrients from meat.)
  4. Feeding gut bacteria:
    Finally, the argument is made that we should eat fermentable fiber to feed our gut bacteria.
    Although there is much interesting research into the role of gut bacteria in health, it is far from conclusive what the best health practice is with respect to them.
    As a researcher aptly pointed out in an editorial last year:

    “This considerable increase in the number of [publications devoted to the study of digestive microbiota] has generated assumptions and speculations on the role of digestive microbiota in human and animal health are likely far beyond our current knowledge.” — Didier Raoult. Digestive microbiota and its influence on health: Facts and myths. Microbial Pathogenesis. 2013 Aug-Sep;61-62:A1. doi: 10.1016/j.micpath.2013.05.008. Epub 2013 May 27.

In sum, I respectfully disagree with Mark Sisson’s statement that the question “Do You Really Need to Eat Vegetables to Be Healthy” can be answered definitively, let alone with a “yes”.
I am more inclined to agree with the points he makes along the way: that if you do not eat vegetables, then you should consider eating offal, drinking broth, eating wild game, or taking supplements. In fact, I think those are worth consideration even if you do eat vegetables.

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More Vegetable Depletion Studies

This is just a quick follow-up to the last post, Are vegetables good for you?.
In it I mentioned a study, the only one I knew of that actually compared a diet containing almost no fruits and vegetables, to one high in fruits and vegetables containing antioxidants.
It turns out that a subset of those authors went on to follow this with two more studies designed to elucidate this further.

The first, in 2003,
No Effect of 600 Grams Fruit and Vegetables Per Day on Oxidative DNA Damage and Repair in Healthy Nonsmokers
 has an apt title.
Here’s the abstract (emphasis mine):

“In several epidemiological studies, high intakes of fruits and vegetables have been associated with a lower incidence of cancer. Theoretically, intake of antioxidants by consumption of fruits and vegetables should protect against reactive oxygen species and decrease the formation of oxidative DNA damage. We set up a parallel 24-day dietary placebo-controlled intervention study in which 43 subjects were randomized into three groups receiving an antioxidant-free basal diet and 600 g of fruits and vegetables, or a supplement containing the corresponding amounts of vitamins and minerals, or placebo. Blood and urine samples were collected before, once a week, and 4 weeks after the intervention period. The level of strand breaks, endonuclease III sites, formamidopyrimidine sites, and sensitivity to hydrogen peroxide was assessed in mononuclear blood cells by the comet assay. Excretion of 7-hydro-8-oxo-2′-deoxyguanine was measured in urine. The expressions of oxoguanine glycosylase 1 and excision repair cross complementing 1 DNA repair genes, determined by real-time reverse transcription-PCR of mRNAs, were investigated in leukocytes. Consumption of fruits and vegetables or vitamins and minerals had no effect on oxidative DNA damage measured in mononuclear cell DNA or urine. Hydrogen peroxide sensitivity, detected by the comet assay, did not differ between the groups. Expression of excision repair cross complementing 1 and oxoguanine glycosylase 1 in leukocytes was not related to the diet consumed. Our results show that after 24 days of complete depletion of fruits and vegetables, or daily ingestion of 600 g of fruit and vegetables, or the corresponding amount of vitamins and minerals, the level of oxidative DNA damage was unchanged. This suggests that the inherent antioxidant defense mechanisms are sufficient to protect circulating mononuclear blood cells from reactive oxygen species.”

In other words, the conclusion is that in healthy people not exposed to high oxidative stress, extra exogenous antioxidants don’t improve things.

Oddly enough, the second, in 2004, The 6-a-day study: effects of fruit and vegetables on markers of oxidative stress and antioxidative defense in healthy nonsmokers has a less decisive title, and reports less decisively negative results, but judging by the description of the subjects and methods, it appears to be a different report on the same study.
I’m not sure what to make of that.
In the discussion they say:

“There is only limited evidence that antioxidants in fruit and vegetables influence oxidative stress or antioxidative defense in healthy subjects. In particular, the contribution of nonnutritive antioxidants to the prevention of oxidative damage is uncertain. The present biomarker-based, fully controlled human intervention study supports the hypothesis that nonnutritive factors, as well as nutritive ones, in fruit and vegetables may influence oxidative damage; however, the effect is not uniformly protective and depends on the molecular structure targeted by each biomarker. ”

It’s not very conclusive.

I’m not going to try to interpret these studies right now, but I wanted to list them for those interested in the topic.

One problem that is interesting to me, though, is that they wanted to keep the macronutrient profiles of the groups the same.
So they gave the non-fruits and vegetables group a drink containing some 60g of simple sugars.
So one could argue that the fruits and vegetables group were at an advantage, because in addition to getting the simple sugars, they were getting factors that mediate sugars, that is, the fiber and possibly the antioxidants.
While fiber is probably not beneficial in and of itself, if you are eating sugars, it can help moderate the damage.
Similarly, if the conclusion from the first study is right, then the times you are going to see an effect of antioxidants, are the times when there is oxidative stress.
Sugar consumption is one such candidate.
So we’ve found ourselves in the situation of comparing apples to sugar.

On the other hand, if they had not done that, then they would be comparing diets either with different caloric intake, or with differing proportions of carbohydrates.
Then if the group not eating so many plants had fared better, it would not have been clear if the effect came from a negative effect of plants, or from the lower calorie / carbohydrate intake.
Although this might appear to be a sloppy design, it’s actually perfectly relevant, because it would address the question of whether or not it is warranted to tell people to replace some of their calories with more fruits and vegetables.
This is a much more realistic question than whether we should tell people to get their carbohydrates from sugar-water as opposed to from fruits and vegetables.

Nonetheless, for some reason, the addition of fruits and vegetables to the diet is heavily advocated, even without such studies in existence.

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Are vegetables good for you?

Before I begin, let me briefly talk about my biases.
I would like to emphasize that I always loved eating vegetables.
Even as a child, I enjoyed eating the lowliest, most hated of vegetables, including spinach, broccoli, peas, turnips, and just about everything my talented cooks of vegetarian parents offered me.
Later I discovered, quite by accident, that my most acute health problems could be completely alleviated by going from a very low carbohydrate diet that included large portions of non-starchy vegetables, to an essentially carnivorous one.
However, I mostly have assumed that this drastic health improvement has been in spite of avoiding vegetables.
I have been more likely to hypothesize that this difference is down to extreme carbohydrate intolerance, a need for a particularly deep therapeutic level of ketosis, or that I perhaps have some micro-organism invading my body, such as candida, that will flourish to my detriment even on cabbage, but will leave me alone if I eat only meat.
More recently, and rather reluctantly, I have had to examine whether, in fact, vegetables themselves, or at least some of them, are what is causing me harm.

In this post, I want to point to two sources that have helped me understand and embrace the idea that vegetables not only are not necessary for good health, but they may actually do harm in many people.

The first is a curious small study from 2002 in the British Journal of Nutrition.
The point of the study was to see if the anti-oxidants in green tea have a positive effect on oxidative markers of stress.
In order to make sure the effect was coming from the tea, they removed all fruits and vegetables (except potatoes and carrots) from the subjects’ diets.
The researchers didn’t find any long-term effects from the green tea extract, but they did notice something interesting.
The removal of flavonoid containing elements of the diet did improve those markers.
A “decrease in protein oxidation, in 8-oxo-dG excretion and in the increased resistance of plasma lipoproteins to oxidation in the present study points to a more general relief of oxidative stress after depletion of flavonoid- and ascorbate- rich fruits and vegetables from the diet, contrary to common beliefs.”
In other words, it appeared in this study that not eating fruits and vegetables was better for the participants than eating them.
If nothing else, this must give one pause.

The second I came upon just this week.
At the 2nd Annual Ancestral Health Symposium 2012 (AHS12), Georgia Ede, M.D. gave her presentation titled “Little Shop of Horrors? The Risks and Benefits of Eating Plants”.
In it and on her website, she points out that there are no studies that she could find (and the above is the only one I know of) that actually compares diets with and without vegetables.
The studies that she did find that showed positive benefits to eating vegetables are all flawed in some way such that it can not be determined which aspect of the intervention gave a positive benefit.
For example they had people eat more vegetables and less refined sugar, or eat more vegetables and exercise more.
Moreover, the only studies she found that did not have these confounders, had negative results, that is, they did not show the benefits the researchers were expecting.
Of course, this is only absence of evidence, but with the extensive promotion of vegetables that we are exposed to so vigorously, one would hope to see something more concrete behind it.

Dr. Ede notes that there have been groups in the past that survived fine without vegetables.
She makes cogent arguments against the assertions that fiber is beneficial, and that vegetarians are healthier than non-vegetarians.
She shows that micronutrients are more abundant and/or more bioavailable in animal foods than in plants.
Yet the most important insight she provides from my perspective is that there are many compounds in plants that function as protection for the plant, to prevent it being eaten.
Even though many people can tolerate them at low levels, in high doses (or low doses for sensitive individuals) they are at best double edged swords, and at worst harmful.
This is true even of compounds that have been touted as health-promoting, such as anti-oxidants.

She promises to write about many classes of toxins, and the first article has already been written.
It describes the problems with brassicas (a.k.a. cruciferous vegetables).
When I was on a simply low-carb diet, instead of a “zero-carb” diet (that’s a bit of a misnomer, since there are trace carbs in meat, and I sometimes eat liver or cream, which have a bit more) I ate a lot of those, because they are very low in carbohydrates.
As she claims seems to be the pattern, the ingredients in brassicas that are advertised as fighting disease, also cause problems, actually poisoning mitochondria, generating ROS’s, and more.
I recommend reading her post, and the rest of her site.

I’ll leave with a quote that particularly struck me from the AHS talk:

26:37

“[P]erhaps these compounds are really only irritants that we’ve had to evolve to deal with because we happen to eat them, and maybe [it’s not the case] that they’re actually good for us.”