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Plant Protective Substances: Listing alphabetically & by Hazard

Plant protective substances, including histamines, Lectins, Oxalates, Furocoumarins, and Cyanogenic glycosides, are ranked by plant and herb.

FrugalDoc

10/1/20262 min read

Plant protective substances are not "deadly" like some pathogens. However, in people with poor gut function, poor immunity, or general poor health, they can wreak havoc in the gut and beyond.

This blog lists various vegetables, fruits, herbs, and spices, their protective substances, how much of each substance they contain, and their relative hazard.

It also covers preparation methods that reduce the harm these substances can cause.

Click to download PDF

Plants' protective substances - alphabetical list

Click to download PDF

Plants' protective substances - by hazard level

Humans have adapted to and dealt with plant-protective substances since we have been on Earth. Something has changed within us since the Industrial Revolution. Arguably, the biggest change is how our gut functions. You are what you ABSORB - NOT what you eat.

Historically, we cooked to prolong the food's "shelf life" and improve digestion. We also used other methods, like fermenting and salting.

Here is how you use this page and the files if you want to reduce the potential harm possible from these plant-based substances. This is particularly important if you have one or more nagging chronic conditions that remain unexplained.

Step 1: Eliminate all plant-based foods for 2-6 weeks. If you notice a positive impact on your health, congratulations, you found a cause.

Step 2: Reintroduce foods, but prepare them through cooking as outlined below.

Step 3: Work on improving your gut function. This is step 3, not step 1, because if you are sensitive to plant substances, that could impede the gut repair process.

Step 4: You may now consider introducing raw vegetables again, but choose those lowest in potentially harmful constituents (see the PDF files).

"Raw" is actually a modern fad, so favor cooked over raw vegetables when you can.

Cooking and Processing Methods, by Constituent

Lectins (heat-labile proteins):

  • Boiling/thorough cooking is essential and far more effective than soaking (soaking alone reduced pulse lectins only 0.1–5.2%).

  • At least ~10 min of proper heat is needed; soaking and dehulling do not remove lectins (they reside in the inner seed).

  • Kidney beans: soak, discard soak water, then boil vigorously (not low-temperature slow-cooking, which can leave phytohemagglutinin active).

  • Fermentation and germination are useful adjuncts.

Oxalates (remove water-soluble fraction by leaching):

  • Boiling is most effective (soluble oxalate ↓30–87%) vs steaming (5–53%); baking gives no loss. Discard the cooking water.

  • Cooked spinach has ~1/5 the oxalate of raw.

  • Soaking legumes reduces total oxalate 17–52%.

Cyanogenic glycosides (cell disruption + enzymatic hydrolysis + volatilization/leaching):

  • Multi-step traditional processing is most effective (cassava boiling, drying, parboiling, etc.: 25–98% loss).

  • Soaking followed by boiling beats either alone; sun drying > oven drying.

  • Grating + dewatering + fermentation + roasting (gari/fufu) removes 80–95%.

  • High-cyanogen cassava (>250 µg CN eq./g) is hard to bring to the ~10 µg/g safe target with a single method.

Furocoumarins (reduce via processing/source control, not home cooking):

  • Commercial processing lowers content (hand-squeezed grapefruit juice ~2–3× commercial).

  • Avoid peel/zest — peel carries far higher concentrations than pulp.

  • Cultivar choice: mandarins nearly devoid; grapefruit, pummelo, lime high.

  • No established home cooking method destroys furocoumarins; control the source.

Histamine (a biogenic amine, largely heat-stable — control formation, not destruction):

  • Cooking does not reliably destroy preformed histamine; the mainstay is preventing its formation.

  • Prioritize freshness: buy and eat perishable produce (especially spinach and other leafy greens) fresh; refrigerate promptly and avoid prolonged storage, which allows microbial histamine accumulation.

  • Limit or avoid fermented plant foods (sauerkraut, kimchi, fermented soy, olives, pickles) in histamine-intolerant patients.

  • Susceptible patients (low DAO activity (the histamine-reducing enzyme), DAO-inhibiting drugs, alcohol) react at doses healthy people tolerate; co-occurring putrescine/cadaverine worsen effects by competing for DAO.