Dr Kurt Harris - questions the empirical basis for the universally accepted support of higher fruit and vegetable diets: Archevore - Archevore Blog - William Munny eats his vegetables
Extract:
"At the same time as I’ve scoffed at the cultural obsession with fruits and vegetables, it has always seemed plausible to me that eating some plant matter along with your animal products is probably healthier than otherwise. It’s just that most of the usual justifications for fruit and vegetables don’t ring true, and the few intervention trials where subjects have been exhorted to eat more fruit, vegetables or fiber have failed to show benefit. Such as:
"At the same time as I’ve scoffed at the cultural obsession with fruits and vegetables, it has always seemed plausible to me that eating some plant matter along with your animal products is probably healthier than otherwise. It’s just that most of the usual justifications for fruit and vegetables don’t ring true, and the few intervention trials where subjects have been exhorted to eat more fruit, vegetables or fiber have failed to show benefit. Such as:
2) WHEL Trial
Note that these trial results leave open the idea that eating some vegetables or fruits is healthier than none. They only refute the conventional wisdom that the more you eat of them, the better.
Analyses of RDA percentages, where vitamin requirements have been derived from the SAD, have never been convincing to me. I have tended to agree with Dr. Bernstein that eating some veggies is a hedge against going without unspecified beneficial compounds.
As I find meals garnished with and flavored by veggies more enjoyable, I’ve eaten plenty of veggies and some fruit even when I’ve been eating VLC. My addition of starchy vegetables (and limited rice) 6 months ago was purely for reasons of physical performance due to increased physical activity.
So to date I’ve felt that animal products should generally be favored over plants (If forced, take the steak over the potato) but eating some plant based whole foods has had two benefits besides the obvious one of palatability:
1) Eating some starch/ sugars avoids chronic deep ketosis and improves physical performance and work capacity
2) Eating a variety of plants should be a hedge against micronutrient deficiencies in our Neolithic/industrial food environment
I’ve so far read nothing to change my thinking about these intuitions, but now Stephan has recently posted a two part series, replete with up-to-date references, which provide some scientific backing for my rejection of the “magic compounds” meme.
At the same time, he has provided an additional highly plausible reason to include a moderate variety of colorful plants in your diet, besides starch for fuel and the micronutrient hedge.
I’ve clipped some key quotes from these excellent essays, and followed with comments of my own in roman:
Stephan says:
Polyphenols are a diverse class of molecules containing multiple phenol rings. They are synthesized in large amounts by plants, certain fungi and a few animals, and serve many purposes, including defense against predators/infections, defense against sunlight damage and chemical oxidation, and coloration. The color of many fruits and vegetables, such as blueberries, eggplants, red potatoes and apples comes from polyphenols. Some familiar classes of polyphenols in the diet-health literature are flavonoids, isoflavonoids, anthocyanidins, and lignins.
Polyphenols are often, but not always, defensive compounds that interfere with digestive processes, which is why they often taste bitter and/or astringent.
So we are not forgetting that plants can’t run. Plants elaborate defensive secondary compounds, some of which are specifically designed to mess with “plant predators” like herbivores, vegans and even normal people like us.
Polyphenols that manage to cross the gut barrier are rapidly degraded by the liver, just like a variety of other foreign molecules, again suggesting that the body doesn't want them hanging around.
Things that are rapidly arrested by the liver police should not be recruited en masse – this argues against taking antioxidant supplements or try to “load up” on one particular substance.
The most visible hypothesis of how polyphenols influence health is the idea that they are antioxidants, protecting against the ravages of reactive oxygen species.
This is the mainstream view of “antioxidants”. You can’t turn around without seeing an article advocating that we load up on blueberries, or red wine, or green tea, or whatever, for the supposed “antioxidant” effects.
For a good discussion of the basis for this meme - the idea that we need to fight the damage caused by leakage of free radicals from our mitochondrial furnaces with
supplements - I recommend Sex, Power, Suicide by Nick Lane. This book is a must-read.
Suffice to say this antioxidant supplementation idea increasingly seems not just implausible, but totally back-asswards.
Here are a few references that show the perverse effects of trying to fight oxidation by eating excess antioxidants.
6) Lasting antioxidant effect of flavonoid-free diet "
Stephan Continues:
In other words, the benefit of low doses of radiation – the kind we get naturally all the time from cosmic rays and naturally occurring radioactive isotopes – and the slightly toxic colorful compounds called polyphenols found in fruits and vegetables, is that both act through hormesis.
Hormesis is when a small stress induces a healthy response in an organism, such that the organism is healthier than without the stress exposure. Any stress that we have defenses for, that we would expect to encounter on an evolutionary basis, is a candidate to be hormetic. Think of this as a necessary, but not sufficient, set of conditions, though.
The perfect example of hormesis is exercise. Exercise creates oxidative stress, and resistance exercise in particular literally destroys muscle tissue. Hormesis explains the “paradox” (which is no paradox at all) that marathon running and other extreme endurance sports could be quite bad for your health, but that more moderate exercise is much better than no exercise at all.
Stephan Continues:
The body treats polyphenols as potentially harmful foreign chemicals, or "xenobiotics"
Both radiation and polyphenols activate a cellular response that is similar in many ways. Both activate the transcription factor Nrf2, which activates genes that are involved in detoxification of chemicals and antioxidant defense**(9, 10, 11, 12). This is thought to be due to the fact that polyphenols, just like radiation, may temporarily increase the level of oxidative stress inside cells.
Hormesis is when a small stress induces a healthy response in an organism, such that the organism is healthier than without the stress exposure. Any stress that we have defenses for, that we would expect to encounter on an evolutionary basis, is a candidate to be hormetic. Think of this as a necessary, but not sufficient, set of conditions, though.
The perfect example of hormesis is exercise. Exercise creates oxidative stress, and resistance exercise in particular literally destroys muscle tissue. Hormesis explains the “paradox” (which is no paradox at all) that marathon running and other extreme endurance sports could be quite bad for your health, but that more moderate exercise is much better than no exercise at all.
