The first article in this series was a rant - now it’s time for serious biology, and some solid information about the other motive for recommending this principle.

Spoiler: this one is about hedging too. And, once again, about an unusual perspective on this widely repeated piece of wisdom.

What if… all of this actually made sense?

In the first installment I asked what is so remarkable or healthy about “yellow”, “red” or “green” in the first place. Today it’s about the exact opposite question: Is there anything unhealthy about “red”, “yellow” or “green”?

Ingredients: harmful or valuable?

Everyone is always very excited about the heroes of the plant world: “secondary plant compounds” (phytonutrients), fibre and antioxidants. Not to mention the minerals and trace elements. They are the stars of the plant kingdom’s marketing department.

Nobody, on the other hand, pays attention to the villains, the bad guys: , goitrogens, oxalates, cyanogenic glycosides, tannins, phytates and other :

Plants - just like animals - don’t want to be eaten. And that goes double for their seeds: they can’t run away, can’t kick and can’t bite, but they can defend themselves chemically: many compounds in plants are toxic. Some of these poisons the human body can tolerate in limited amounts, or render harmless. Others must, or should, be defused before consumption.

The alternative rainbow

Red: not one to try at home: raw kidney beans can land a person in hospital in very small numbers. The reason is the phytohaemagglutinin(1) they contain, a lectin, and therefore a so-called antinutrient - and a particularly potent one at that. It can be rendered harmless by soaking (pour the water away) and boiling(2) - and it has to be, for the beans to become edible in the first place.

Beige/yellow: wholegrain cereals contain many nutrients the body needs - but also phytates, which bind those nutrients (and others eaten together with the wholegrain) in such a way that the body can’t absorb them. They can be neutralised, or have their effect reduced, by a sufficiently long sourdough fermentation.

Brown (3): almonds, especially bitter almonds(4), contain a so-called cyanogenic glycoside (amygdalin), as well as the enzyme beta-glucosidase - two compounds stored independently and separately that react to form cyanide (prussic acid) when brought together. They are brought together, for example, by mechanically destroying the almond kernel - also known as “chewing”.

Green: Brussels sprouts and broccoli - the darlings of every nutrition counsellor - contain so-called goitrogens: substances that promote goitre formation in humans by inhibiting the thyroid’s iodine uptake. And goitrogens don’t care about their position in the rainbow: soybeans, millet, cassava and even pale cauliflower carry them too.

That already gives us - by way of example - several colours of the rainbow together - and with them the less advantageous substances they contain. (5)

Oh come on, surely it’s not all poisonous…

True: none of it (except phytohaemagglutinin) is (for most people) acutely toxic - many of these foods are tolerable for many people. But the tolerance threshold differs from person to person. How does the saying go?

The dose makes the poison…

…but nobody lets us know how large or small the dose is, nobody mentions the time span over which that unspecified dose applies(6).

After all, one cigarette doesn’t get you admitted to a hospice with lung cancer on the spot either.

Side track: different digestive systems

Let’s look at how different animals digest their food and deal with nutrients and poisons:

Monogastric digestion (1)

Humans, pigs and others have a relatively identically built digestive system. Simplified: mouth, oesophagus, stomach, small intestine, large intestine.

The large intestine’s main job is the extraction of water - a little fermentation happens too, but comparatively little, and the large intestine is mostly not responsible for absorbing nutrients.

Poisons reach the small intestine straight after the stomach - without having been “treated” beforehand. Poisons are therefore tolerated only in small amounts. One of the consequences when the body detects toxins it can’t tolerate? Diarrhoea.

Monogastric digestion (2): “hind-gut digesters”

Hind-gut fermenters (such as gorillas, rabbits, horses, elephants and others) take this further: where humans have a very short caecum, they have substantially more of this gut section that in humans is merely a “leftover”. Significant fermentation happens there, and the bacteria living in that part of the gut produce essential nutrients. In these animals, too, the large intestine isn’t equipped to absorb those nutrients - so they have to partly eat their own faeces again to absorb them(7). 🤢

Here, too, toxins pass straight from the stomach into the small intestine, so these animals also tolerate poisons only in limited amounts.

Ruminants

These have a multi-stage digestive tract, in whose various stages bacteria can render plant poisons harmless before they even pass the small intestine, fermenting them and making them usable. A kind of “sourdough fermentation inside the body”, if you will.

That’s why ruminants can cope with a whole lot more compounds than monogastric animals - humans included. They run very effective “upcycling” of antinutrients. What soaking, fermenting or cooking is for humans is already built into the cow by nature.

Eat the Rainbow: the other reason

Let’s get back to the reason I wrote this second article on the “eat the rainbow” principle, and to the reversal of perspective - once again:

What if the rainbow is just a welcome method of “hedging"(8) - the spreading of a risk? In Part 1, hedging was still the linguistic hedge (“eat as many different foods as possible - sooner or later you’ll probably hit enough good stuff”); here it’s portfolio theory: “Don’t bet all your antinutrients on a single hand - diversify your poison portfolio”.

The appeal to “eat the rainbow”, if followed, automatically leads to a greater variety being eaten, so that the most diverse antinutrients from each individual source are automatically limited in quantity.

And we hope that this keeps the acutely toxic threshold - over the course of our entire lives, and different for every person - from being exceeded.

Fingers crossed! 🤞

Related articles

Two combine harvesters in a large wheat field.
Grains

Grains are among the most fundamental staples - most people can hardly imagine doing without them. Yet depending on whether they are eaten by humans or fed to animals, they are credited with diametrically opposite properties. Schrödinger’s food

Colourful breakfast things in a bowl. Probably not healthy, but fitting for the rainbow theme
"Eat the Rainbow"

A popular piece of advice, and what my brain does with it when reading it creatively - and from contrary experience. A rant.

  1. Wikipedia: Phytohaemagglutinin
  2. At a rolling boil at 100°C! Not in the slow cooker! For long enough!
  3. Yes, I know brown isn’t a rainbow colour. Thank you for the correction - sit down.
  4. In sweet almonds these substances have been reduced by breeding (but not eliminated). Incidentally, bitter almonds are what give marzipan its typical flavour in the first place. Without them it would simply be sweet almond paste. And conveniently, they’re already “pre-chewed” there (9)
  5. This list could be continued indefinitely: all plants are toxic in one way or another, and for one species more, for others less. But some poison doses are tolerable - for example because they have been “bred out” and their amount is small enough.
  6. Wikipedia: Paracelsus: “All things are poison, and nothing is without poison; the dose alone makes it so that a thing is not a poison.”
  7. Wikipedia: Coprophagia, Cecotrope
  8. Hedging was already a component in Part 1
  9. Prussic acid (hydrogen cyanide) has a very low boiling point, and marzipan is heated during production, so most of it is no longer present in the final product: another example of the need to detoxify plant foods before eating them. But good for another punchline, which I naturally couldn’t deny myself. (10)
  10. Let’s just hope handing out footnotes for footnotes doesn’t catch on…