Superfood or Antinutrient?
Nutrient Density and Composition in Plants
Nominally, plants contain some substances the body needs, some it tolerates, some it doesn’t require, and some it would be better off not exposed to.
I’ve covered this in a few other articles already: alongside their valuable ingredients, every plant also carries antinutrients that (more or less) severely impair the absorption of those nutrients. The bioavailability of the ingredients in plant-food is usually much lower than in animal-based food - and that holds even for otherwise well-bioavailable foods. Example: oysters contain highly available zinc. Eat oysters together with corn, and the body absorbs next to none of it (1) . In the end, the nutrient content hardly matters - what counts is solely the availability of those ingredients.
And finally, human nutrition science and agriculture can’t agree on the properties of plants: both, for instance, consider grains indispensable - one side cites health reasons for humans and is delighted by the fibre that helps with losing weight. The other uses it because it makes their animals fatten up and reach slaughter weight faster.
Last time I checked, humans counted as animals…
A small selection of antinutrients already appeared in Part 2 of “Eat the Rainbow”, here are a few more, plus whole families of antinutrients.
Three Kinds of Antinutrients
Before we get to the list, a classification is worth it. “Antinutrient” throws very different substances into one pot. Three categories are more helpful:
- Passive binders - bind a nutrient into an unusable complex and leave the body together with it. The only damage is the lost nutrient. That bound nutrient can, however, also come from other (otherwise well-available) foods, as you can see in the oyster/corn example above.
- Active disruptors - interfere with a process: they block a digestive enzyme, hamper iodine uptake, or destroy a vitamin. They don’t just hide a nutrient, they sabotage the machinery.
- Directly harmful / toxic - damage cells or tissue, or simply poison. Since we’re talking about food, the dose is naturally relatively low. But it’s enough to cause some people trouble.
Some substances sit in two categories at once - oxalate and saponins are the obvious double agents.
Here as everywhere: personal tolerance thresholds vary, and depend on the substance taken in.
The order isn’t a ranking: substances covered higher up simply come before those covered lower down in the alphabet.
Cyanogenic Glycosides
Category: directly toxic
When they are brought together (2) with the enzyme beta-glucosidase (which the plant parts also supply, but keep strictly separate), hydrogen cyanide (cyanide) forms, which is acutely toxic. More a poison than a true antinutrient, especially since it isn’t present directly in the food but is only formed later. Listed here to round off the harmful end.
Specifically: linamarin (cassava), amygdalin (bitter almonds, apricot kernels).
On almonds - though the colour doesn’t quite fit - there’s already a treatise with various footnotes in Part 2 of the Rainbow Appeal.
Goitrogens / Glucosinolates
Category: active disruptor
Goitrogens disrupt iodine uptake and thyroid-hormone production - risk of goitre, especially when iodine supply is already low.
Specifically: breakdown products of glucosinolates - goitrin, thiocyanate, isothiocyanates
Found in: cruciferous vegetables (cabbage, kale, broccoli).
Interestingly, the same substances are also studied as protective phytochemicals - dose and iodine status decide. Dosing via a diet of goitrogen-containing plants is, however, hardly possible given the unknown actual dose per portion.
A combination of iodine supplementation/thyroid treatment and goitrogen-containing foods strikes me - without any medical training - as rather dubious, though. Personally, I’d rather strike one colour or another from the rainbow than supplement against them.
Lectins
Category: directly harmful (umbrella term: carbohydrate-binding proteins)
These substances bind to the intestinal epithelial cells, can damage the gut lining, disrupt absorption, and clump red blood cells together.
- Phytohaemagglutinin (PHA) - red kidney beans; raw or undercooked it leads to acute vomiting and diarrhoea, even from just a few raw beans.
- Wheat germ agglutinin (WGA) - wheat; binds glycoproteins of the gut wall (since wheat is present almost everywhere: many people have a high tolerance threshold, but because of that they rarely realise that this ubiquitous food could be the cause of their problems). Similar: peanut lectin (PNA), soybean lectin (SBA).
- Ricin - castor beans; an extreme outlier, a lethal poison (not a food, but the same protein family).
Some of these substances (PHA) are largely destroyed by sufficient soaking and cooking. Others (WGA, PNA, SBA) are extremely stable and survive heat (boiling, baking), stomach acid, and digestive enzymes - they can thus reach the gut almost unchanged. SBA needs massive pressure (pressure cooker) or industrial processes to denature.
Oxalates (Oxalic Acid, Oxalate Salts)
Category: passive binder + directly harmful
Oxalates form insoluble crystals - calcium oxalate, for example. They bind calcium, but are also directly harmful in themselves, because the crystals are very pointed or sharp and therefore tissue-irritating. A very multifunctional substance.
Found in: spinach, rhubarb, chard, beet greens, almonds.
Oxalates are stored in the body and can cause problems not only when eaten but when they’re released. That can happen when you specifically avoid oxalates for a while and the body sees an opportunity to break down the previously stored oxalates again(3). The symptoms that then appear are usually attributed to the new diet, even though it’s the body “clearing house”, finally able to reverse the storage of oxalates. Many kidney stones consist of calcium oxalate. The crystals are needle-like and can become quite painful.
Phytic Acid (Phytate, IP6)
Category: passive binder
Phytic acid serves the plant as a store of phosphorus. In the human digestive tract it binds above all iron, zinc, calcium, and magnesium, and thus effectively prevents the absorption of these minerals - not only from the plant parts that contain phytic acid, but also from other foods eaten at the same time.
Found in: whole grains, legumes, nuts, seeds (in bran and hull).
The textbook case of the passive binder - and at the same time the neatest proof that “antioxidant” and “mineral thief” are not a contradiction here but the same action. Free iron is a catalyst for oxidative reactions (see the Fenton reaction(4)). Bind the iron away and you suppress those reactions - which is precisely what gets celebrated as “antioxidant activity.” It’s the same grip on the same iron, marketed once as rescue and once as theft. You can’t order the one and cancel the other.
Ironically, then, foods like whole grains come with the nutrients they’re praised for and, at the same time, with antinutrients that block the absorption of said nutrients.
Nutrient Density
Explore Phytates further, showcased on Magnesium from Wheat: Why more isn’t always better…
New ND SimulationProtease and Amylase Inhibitors
Category: active disruptor
- These substances block digestive enzymes - protein and starch digestion suffer; chronically high intake burdens the pancreas.
Specifically: trypsin inhibitors (soy: Kunitz, Bowman-Birk), alpha-amylase inhibitors (beans/wheat - the molecule behind the “carb blocker” supplements). Found in: (protease inhibitors) legumes, grains, potatoes; (amylase inhibitors) grains and certain beans
Trypsin is a protein-digesting enzyme - blocking it can, e.g. with high raw-soybean consumption, lead to animals being chronically undernourished even though they nominally eat a large amount of protein that they then can’t make use of.
White kidney beans contain phaseolamin, which is even sold in isolated form as a carbohydrate blocker in diet pills, to artificially sabotage starch absorption in the gut. Yet another example of the inherent limitations of the caloric balance. But what a bizarre idea, to pay money to torpedo your own metabolism so that you can keep eating carbohydrates unchecked (instead of simply going without both).
Since these are protein-based antinutrients, they can be denatured by heat. Some, however, need moist high heat (boiling, steaming); roasting is less effective for them.
Saponins
Category: active disruptor + harmful at high doses
Saponins act like detergents (soaps) - they disrupt cell membranes, can increase gut permeability, and bind cholesterol and minerals; at high concentration they are harmful to red blood cells (haemolytic).
Found in: legumes, quinoa (in the bitter coat).
The cholesterol binding is often sold as an advantage, but it doesn’t just disrupt that one aspect on purpose - it acts far more broadly.
More about 'detergents' in foods
Evolutionary Association, Chapter 7: Emulsifiers
Tannins (Condensed Polyphenols)
Category: passive binder
Tannins bind non-haem iron and dietary protein - iron absorption and protein digestibility fall. (This is why tea with a meal dampens iron absorption significantly.)
Found in: tea, coffee, red wine, sorghum, the seed coats of legumes.
Labelled “secondary plant compounds”, tannins on the other hand count once again among the ingredients for which plants are praised. We see: plants should be both eaten and avoided - or at least judged sceptically - on account of their “secondary plant compounds”.
Two Patterns That Emerge
Two patterns stand out:
Some antinutrients are heat-sensitive or can be reduced by suitable processing. Lectins, protease inhibitors, cyanogenic glycosides: boiling, soaking, fermenting, or sprouting push them down sharply. The scary ones are largely a raw-food problem.
Phytate and oxalate are the stubborn exceptions, and yet oxalate-rich plants like spinach are happily traded as superfoods - in real life, not in cartoons.
Some antinutrients are at the same time celebrated phytochemicals. Phytate (antioxidant), glucosinolates (cancer research), saponins (cholesterol), tannins (the polyphenol halo).
The same molecule is “antinutrient” or “superfood compound” depending on who’s writing - a nice example of how interpretation, not chemistry, drives a large part of the nutrition narrative.
The dominant source of antinutrients also shows us that they’re especially present in the living things that can’t defend themselves mechanically or get away: plants have no claws, teeth, or legs, and defend themselves against their predators chemically.
Since evidently not everyone feels immediately unwell from eating plants (while some observe a massive improvement in their health when they avoid certain or even most plants), we also see that the tolerance thresholds vary from individual to individual.
The widespread message “more plant foods help” can therefore have negative to fatal consequences - and since, thanks to the usual narrative, hardly anyone comes up with the idea on their own that health problems might have their causes in antinutrients, it’s important to bring this aspect into awareness too.
Hold on - one more. Admittedly tacked onto the end somewhat artificially:
Additionally, Outside the Competition: Fibre
Category: personal villains
Fibre is, in dietary counselling, not only above suspicion but indispensable. Personally, however, I’ve found that it does cause me problems - so I’m including it in this list as a bonus:
Fibre likewise inhibits the absorption of various substances - interestingly, both of nutrients and of antinutrients. Perhaps it’s so praised because it also blocks antinutrients; I would, however, prefer to take in neither nutrient blockers nor antinutrients: both are unnecessary, if both are avoided at the same time.
What I find interesting about fibre is the shifting messages: for various conditions, “low-fibre bland diet” applies during acute phases. Once the gut has calmed down again afterwards, the unanimous advice is once again to increase intake… until the next acute phase. So what makes us healthy, by this logic, doesn’t seem to be the same thing that keeps us healthy. That’s an assumption that doesn’t match my experience.
Personal Conclusion
I personally know several plants that are acutely harmful to me, triggering inflammation immediately, yet count among the staple foods of plant-based eating. And there are several further suspects I haven’t investigated closely enough. Admittedly: my interest in these experiments is very low, since I deeply value the now long symptom-free phase.
By now, I know a few plants that my body seems to tolerate, that don’t seem to cause any trouble. These, by far, aren’t making up a complete diet though.
A restriction to a purely plant-based diet, or just a largely plant-based diet, is therefore not an option for me and my health.