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A lot of paleo thinkers seem to be rather sceptical of plants by default, preferring to 'eat food that can't defend itself after it's dead,' and assuming that plants are essentially out to get us, using whatever chemical means they can to stop us eating or fully digesting them. At the same time, many paleos think that select fruits and vegetables can be part of a healthy paleo diet and indeed part of the optimal paleo diet.

The historical evidence is much debated over, modern day hunter gatherer diets seem mixed. What I'm interested in working out is which plant foods- if I'm going to eat any at all- would be the safest candidates for staples of my diet. Tubers are a natural suggestion, but potatoes are related to nightshades and contain glykaoalkaloids, sweet potato contains cyanogenic glycosides. Leafy greens like spinach might seem to be a natural foodstuff that would be plentiful and easily gatherable throughout our evolutionary past, but they are full of oxalate and rubiscolin. Crucifers like cabbage, brocolli, kale etc are notoriously healthy, but are goitrogenic. Most fruits seem safer, but on the other hand are far more full of fructose, one of the most anti-paleo substances there is.

So the main things to consider seem to be:

  • Which foods are safe, or can be made safe by certain treatments, from the point of view of anti-nutrients?
  • Which foods are optimal from the point of view of being made up of starch (which needs to be processed but yields glucose) versus fructose?
  • Ought we to favour foods like berries which are packed with 'phytonutrients' and antioxidants or should we be wary of these plant chemicals?

Obviously the thing that ultimately counts is the hard physiological analysis of each of the respective chemicals, but since the data here would be ludicrously expansive and detailed, I think a paleo perspective on- what would we actually have evolved to eat?- is particularly useful.

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6 Answers

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The online paleo community is really hating on fruit these days, but it is the one plant that seems to want you to eat it. It does not, as you say, try to defend itself after it's dead.

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 The fruit wants to be eaten, that's right, but (as Dan Dennett would say) cui boni. Who is benefiting? The fruit tree or the human? Or could it be a beneficial for both, like a symbiosis? I don't know. By the way, I eat fruits quite often... – Pieter D Apr 13 2010 at 13:25
Agreed, though fruit don't seem to want us to fully digest their seeds, it doesn't seem that they do this by radically disrupting our digestion. – David Moss Apr 13 2010 at 15:43
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 Possibly they are using us as a vehicle to transport seeds to be deposited in new locations. – henny Apr 13 2010 at 16:03
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 Fruit as fruit is okay to some (not to my metabolism) but too many think fruit anything (juice, sauces, etc) is okay. It is sugar- plan and simple. Some have fiber, some don't have enough and oranges are the worst. OJ commericals are all lies. – pjnoir Apr 13 2010 at 20:25
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from what I'm seeing on Goitrogen, cooking the veg + adding saturated fat and possibly salt as a source of iodine = nothing to worry about (saturated fat, coconut and avocado all have the opposite affect of Goitrogen foods)

of course you have to remember this: anything in large enough amount is and can be poison. Often the same thing in small or moderate amounts is safe (e.g. water etc).

so for most things you eat it goes from negligible, to good for you, to safe, to possibly problematic/allergenic, to toxic, to silliness/madness/death.

fructose in small amounts (or spread out over a month or year) isn't going to be as dangerous as eating a whole jar of honey all at once, concentration and your body's ability to deal with it will be the issue for that.

I personally go by this the only reasonable paleo principal if its nothing but bad I don't' eat it, if in small amounts or as part of a balanced diet (e.g. it will do more good than harm especially mixed with something else I'd eat with it anyway, like cooked broccoli with butter) its a non issue.

and besides we seemed to have evolved fire + cooking before agriculture so fermenting/storing/preserving foods + cooking them to make them more edible seems to have a much longer evolutionary pairing with us than most agriculture centered foods.

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Lots of good points, agree that goitrogens can be deactivated easily by heat, though crucifers contain all manner of other exotic chemicals that may be good/bad. PaNu's paleo principle only really helps us if we know already what is harmful and why, it doesn't really help us work out what precise things are paleo/probably safe and in what quantities. I agree about cooking, but that opens up a whole new set of issues: whether we should generally eat plants so they're highly deactivated and 'safe' or close to their fresh, raw state. – David Moss Apr 13 2010 at 18:06
Well I feel like we somewhat do have a way to decide what's safer/ better , our tongue, whatever form taste better/satisfys more is generally coupled with what our current nutritional needs are (E.G. crave salty stuff when your body needs it, crave certain foods that are high in whats currently lacking) I've seen a couple studies on this, and I'm assuming going to plaeo and dropping the sugar addiction would clear up the conscious choice and unconscious craving aspect of it. Cooking/fermenting was to preserve and enhance nutritional value pretty much. But yeah safe/better is a per food basis – Quik77 Apr 14 2010 at 18:18
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I filter food choices through the Paleo lens, that's for certain. Fruit in particular is problematic for me. Likely a human of N. European descent as myself, would have had scarce access to fruit. Certainly NOT the modified/selected hyper-large, hyper sweet fruit of today, and in no where near the abundance nor variety. Frankly, neither would equatorial descendants!

I do not attempt to recreate our Paleolithic past! As Kurt Harris at PaNu blog points out, just use Paleo as a guide or filter to foods and lifestyle and activity and rest.

All the plants listed by David Moss have their drawbacks, for certain. Perhaps the intake of minor quantities of the anti-nutrients in various plants result in hormesis, a low dose of "poison" or stress that makes us stronger and more able to cope with other stressors. It is difficult to be so reductive in analyzing the troubling substances in various plants.

I suppose the question remains, what are the best plant foods? It may be easier to simply eliminate the WORST plants first (grains, legumes, many fruits perhaps?) and work backwards that way.

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agreed with this approach, worrying about them all the time seems like the worrying itself would be more of a stressor than eating one piece of one of the above would be. – Quik77 Apr 13 2010 at 16:10
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 One can easily avoid something without worrying about it. – Ambimorph Apr 13 2010 at 19:42
I agree I think what is healthy for each of us depends on our individual genetic make-up and health history. As a group we tend to forget that although large amounts of grains, dairy, legumes and some fruits, veges, and nuts are maladaptive for humans, it was actually VERY adaptive for our Paleolithic ancestors to add small amounts of dairy, legume, and milk at the beginning of agriculture. These dependable sources of food and the way they fatten us up would have initially given grain, legume, and milk eaters an evolutionary advantage. It's only eating large quantities that causes trouble! – Heidi Oct 27 2011 at 18:40
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Based on what I've read about the most well-known toxins and potential "drawbacks" of each plant family (and as nicely summarised my David Moss in the body of his question), I have basically narrowed down my daily vegetable consumption to zucchini, squash/pumpkin, cucumber, carrots, celery, onions and garlic (and various spices). Not all at the same time, obviously.

These seem to be the least problematic from what I've read, but I'm continually adjusting as I learn more. Almost no fruits but occasionally berries. Occasionally mangetout beans for variety (although doubtful about the lectins...).

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Oh, and I forgot to mention lettuce - for those rare occasions when I want some crunchy, harmless empty calories. – archaea Apr 13 2010 at 16:12
empty OF calories (i.e. low-calorie) I meant, sorry! What I meant is that lettuce satisfies occasional crunch / munchies cravings without providing a heap of unnecessary calories (and not much nutrition, either) – archaea Apr 13 2010 at 16:14
Funny, squashes and carrots are staples for me too, they seem to pack a good carb:nutrient ratio, not contain many controversial compounds (apart from carotenoids!) and the fact that carrots are a root vegetable counts in their favour for me (so does the fact that they've been cultivated from small unappetising, spindly things, yet aren't excessively sugary- presumably little incentive to put off predators). The fact that squashes come in tough packages is probably a good sign too: do you remove the skins? I used to leave them on, assuming that they'd be nutritious, but more wary now. – David Moss Apr 13 2010 at 18:01
I remove the skin from squash before cooking it, mainly because I'm a little paranoid about pesticides on the surface making it into the pulp. Obviously not an issue if you use organic squash. I hadn't thought of the plant toxin/antinutrient issue regarding the skin, but it seems reasonable to think there might be a greater concentration of them in the bit of the plant that is meant to do most of the protecting! – archaea Apr 14 2010 at 5:41
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Sure must suck to be any species of herbivore on this planet, what with all those antinutrients and phytochemicals in thier diet! Bet they wish they'd evolved to eat meat!

Appologies for the sarcasm, just wish people wouldn't worry so much. Perhaps I just shouldn't go on this site.

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 Tom, I think the whole point of evolutionary reasoning is that it's species specific- so eating grass all day might work well if you're a ruminant, less well if you're a cat... As omnivores clearly some plants are simply poisonous to us and some are extremely healthy, it seems unlikely that there's a perfectly clear dividing line between the two categories. – David Moss Apr 18 2010 at 6:44
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I recently added the tuber, White Skinned Sweet Potato- The skin is where the benefits are found IN THIS VARIETY. It doesn't screw with my BG numbers. I eat one apple every fewe days when in season (Fall, not when the supermarket sells them) Some blueberries in summer. Both have to be Local. Most fruits are just sugar from a branch. Green leaf veggies are great, tomatoes. No root veggies- they are starch but Im diabetic so I have to be a little more selective.

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 the skin is where the toxins concentrate - this is generally true with plants, but definitely true with the potato. – HealthRediscovery Apr 14 2010 at 3:17
In one of my better Paleo blogs that I read, the skin of the White Skin Sweet Potato contains high concentrations of Vit K and other micronutruients that are tough to get in the diet. I do understand that toxins concentrate in the skin but with this tuber- the skin is where its at and worth the trade off. – pjnoir Apr 16 2010 at 21:36

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