Herbs and Spices

TL;DR. By weight, these are the most chemically concentrated things you eat: the essential oils and polyphenols in a gram of dried oregano or clove outnumber those in a plateful of vegetables. Portions are tiny, which is why almost every impressive laboratory result fails to translate. The genuine health evidence is thin and specific: ginger for nausea has decent trial support, cinnamon has small and inconsistent glucose effects, and curcumin has terrible bioavailability and an inflated literature. What spices reliably do is make vegetables taste good enough to eat, which is worth more than any of their pharmacology. And two carry real hazards: cassia cinnamon contains coumarin, and adulteration with lead chromate is a documented and serious problem.

1. What they are

Herbs are leaves; spices are every other part: bark (cinnamon), root or rhizome (ginger, turmeric), seed (cumin, coriander, mustard), fruit (black pepper, chilli, vanilla), flower bud (clove, saffron stigmas), and resin (asafoetida).

Two dominant plant families supply most culinary herbs:

• Lamiaceae (mint family, square stems): basil, oregano, thyme, rosemary, sage, mint, marjoram, savory, lavender.
• Apiaceae (carrot family, umbels): parsley, coriander/cilantro, dill, fennel, cumin, caraway, anise, celery seed.

Plus Zingiberaceae (ginger, turmeric, cardamom), Lauraceae (bay, cinnamon), Myrtaceae (clove, allspice), Piperaceae (black pepper), Solanaceae (chilli, paprika), Orchidaceae (vanilla), and Iridaceae (saffron).

2. Why they exist and why they are so concentrated

Every one of these is plant defence chemistry (Chapter 1). The compounds we prize are essential oils and phenolics evolved to deter insects, inhibit fungi, and kill bacteria. That they are antimicrobial is not a coincidence; it is what they are for.

There is a well-known and still-argued hypothesis that spice use in traditional cuisines tracks climate: hotter countries use more spices, and the proposed explanation is food preservation before refrigeration. Subsequent analyses have challenged the causal claim, and the correlation is real and the mechanism is plausible.

The spice trade is one of the great engines of world history: the Roman trade with India, the Arab and Venetian monopolies, the Portuguese search for a sea route, the Dutch East India Company's control of nutmeg (including the exchange of Run island for Manhattan in 1667), and the European colonisation of the Indies. Nutmeg, clove, and pepper were worth killing for, and were.

Production: black pepper around 700,000 tonnes (Vietnam dominant); ginger around 4.5 million tonnes; turmeric around 1.5 million tonnes (India ~80 percent); chillies around 5 million tonnes dried. Saffron is the extreme: roughly 150,000 hand-picked stigmas per kilogram, from about 70,000 flowers, harvested in a two-week window, which is why it costs more than gold by weight.

3. How they are grown and processed

Most herbs are easy annuals or perennials. The commercially interesting details are in the processing:

• Black, white, and green peppercorns are the same fruit. Black is picked unripe and dried with the skin, which ferments and blackens. White is ripe fruit with the skin removed. Green is unripe and preserved without drying. Pink peppercorns are an unrelated species.
• Cinnamon is inner bark, peeled, and it curls as it dries. Ceylon cinnamon (Cinnamomum verum) forms fragile multi-layered quills; cassia (several Cinnamomum species) forms a single thick hard curl. This distinction matters and is covered below.
• Vanilla is a hand-pollinated orchid (there is no natural pollinator outside Mexico, a problem solved by a 12-year-old enslaved boy, Edmond Albius, on Réunion in 1841, whose hand pollination method is still used). The green pods have no flavour and require months of blanching, sweating, and drying to develop vanillin. This is why real vanilla is the second most expensive spice.
• Saffron is the dried stigmas of Crocus sativus, a sterile triploid propagated only by corms.
• Turmeric and ginger are rhizomes, boiled and dried for the ground product.
• Cloves are unopened flower buds, dried.

4. What is inside them

Nutrition tables for spices are misleading because they are expressed per 100 g and nobody eats 100 g. Dried oregano is spectacular per 100 g and a teaspoon weighs one gram.

What matters is the compound, and the tiny dose:

The coriander/cilantro soap thing is genuine. A genome-wide association study by 23andMe identified variants near the olfactory receptor gene OR6A2, which binds the aldehydes in coriander leaf, associated with perceiving it as soapy. It affects a minority, varying by ancestry from a few percent to over 20 percent. It is not fussiness.

5. What they actually do in your body

Assessed honestly, because this is where the gap between laboratory and life is widest.

Ginger for nausea: the best evidence here. Meta-analyses support ginger for pregnancy nausea and vomiting, at around 1 to 1.5 g a day, with effect sizes comparable to vitamin B6 and a favourable safety profile. It is recommended in several obstetric guidelines. Evidence for post-operative nausea is reasonable; for motion sickness and chemotherapy-induced nausea, mixed. The mechanism is thought to involve 5-HT3 receptor antagonism and prokinetic effects on the stomach.

Cinnamon for blood glucose: small and inconsistent. Meta-analyses find modest reductions in fasting glucose (roughly 0.5 to 1.3 mmol/L in some analyses) with substantial heterogeneity, and inconsistent effects on HbA1c. It is not a treatment for diabetes and should not displace one. Most trials use cassia, which brings the coumarin problem.

Curcumin: a cautionary tale. It has thousands of papers, real in vitro activity, and:

• Very poor oral bioavailability: poorly absorbed, rapidly metabolised, barely detectable in plasma. Piperine from black pepper inhibits its glucuronidation and raises bioavailability substantially, which is why supplements include it.
• A reputation among medicinal chemists as a PAINS compound (pan-assay interference), producing apparent hits across an implausibly wide range of assays through non-specific mechanisms. A widely discussed 2017 Journal of Medicinal Chemistry review argued it has never been shown to be a specific, druggable agent.
• Human evidence is best, and still modest, for osteoarthritis pain, where several trials find effects comparable to NSAIDs at high supplement doses.
• Turmeric supplements have caused liver injury, with a growing number of cases reported, particularly with high-bioavailability formulations. Culinary turmeric is not implicated.

Garlic is covered in Chapter 40; chilli in Chapter 44.

Peppermint oil for IBS has genuinely good evidence: enteric-coated peppermint oil capsules relieve IBS symptoms in multiple randomised trials and appear in clinical guidelines. It works as a smooth muscle antispasmodic. It can worsen reflux, which is why the enteric coating exists.

Fenugreek has some evidence for glucose control and for milk supply in lactation, both modest.

Antimicrobial activity is real in vitro and does not translate to treating infections in people at culinary doses.

The honest summary: the reliable health contribution of herbs and spices is that they let you eat vegetables, pulses, and whole grains without them being boring, and that they let you cut salt and sugar while keeping food interesting. That is a genuinely large effect, and it is not the one that gets marketed.

6. The two real hazards

Coumarin in cassia cinnamon

Cassia cinnamon contains coumarin at roughly 2,000 to 4,000 mg/kg; Ceylon cinnamon contains almost none (around 5 to 20 mg/kg). Coumarin is hepatotoxic in susceptible people and the EFSA tolerable daily intake is 0.1 mg per kg of body weight.

For a 60 kg adult that is 6 mg a day, which is roughly 1.5 to 3 grams of cassia cinnamon, about a teaspoon. German authorities issued warnings after finding that seasonal consumption of cinnamon-heavy baked goods could exceed the limit, particularly in children.

Practically: occasional use is fine. Daily cinnamon supplementation for blood sugar, using cassia, is the scenario where this matters, and it is exactly what people do. If you take cinnamon daily, use Ceylon (labelled Cinnamomum verum, soft and layered, lighter brown), not cassia (hard, single thick curl, reddish, the default supermarket cinnamon).

Adulteration

Spices are among the most adulterated foods in global trade, because they are high-value, ground into powder, and traded through long opaque chains.

• Lead chromate in turmeric is the worst documented case. Investigators, notably a Stanford team studying lead exposure in Bangladesh, found turmeric being deliberately polished with lead chromate to brighten the colour, producing lead levels hundreds of times above limits and measurable blood lead elevations in consumers. Recalls have followed in several countries.
• Sudan dyes (industrial azo dyes, genotoxic carcinogens) in chilli powder and paprika have caused large recalls across Europe.
• Saffron is routinely bulked with safflower, turmeric, or dyed corn silk.
• Ground spices in general are diluted with starch, husk, and colourings.

Practical defences: buy whole spices and grind them, buy from reputable brands with traceable supply chains and testing programmes, be suspicious of unusually bright colour and unusually low price, and prefer origin-labelled products.

Other specific cautions

• Nutmeg in large doses (one to three whole nutmegs) causes genuine and unpleasant intoxication and poisoning (Chapter 18).
• Liquorice root raises blood pressure and lowers potassium through glycyrrhizin.
• Ginger and turmeric in supplement doses have mild antiplatelet effects; discuss with a pharmacist if you take anticoagulants, and stop before surgery.
• Star anise: Chinese star anise is fine; Japanese star anise is neurotoxic and has contaminated teas, causing seizures in infants.
• Essential oils are not food. Ingesting essential oils, promoted in some wellness marketing, has caused serious poisoning; a few millilitres of some (wintergreen, eucalyptus, clove, pennyroyal) can be dangerous, particularly in children.
• Comfrey and several other herbal teas contain pyrrolizidine alkaloids and cause liver damage.

7. How to use them well

• Bloom whole spices in fat. Most of the aromatic compounds are fat-soluble and volatile. Toasting whole spices dry until fragrant, then grinding, then frying briefly in oil (the South Asian tadka or tarka) extracts far more than stirring powder into a liquid.
• Add hardy herbs early, delicate herbs late. Rosemary, thyme, bay, and oregano survive long cooking and improve. Basil, coriander, parsley, dill, mint, and chives lose everything to heat and should go in at the end.
• Dried is not a substitute for fresh in the delicate herbs. Dried basil, coriander, and parsley are close to pointless. Dried oregano, thyme, bay, and rosemary are genuinely good and sometimes better than fresh.
• Grind your own. Ground spices lose volatile oils fast. Whole spices keep 2 to 4 years; ground ones lose most of their character in 6 to 12 months. A cheap coffee grinder kept for spices is the single best kitchen upgrade in this chapter.
• Store dark, cool, dry, airtight. Not above the hob, where the heat destroys them, which is where almost everyone keeps them.
• Use them to replace salt. This is the most useful practical application: acid, heat, and aromatics let you cut sodium substantially without the food tasting flat (Chapter 57).
• Turmeric with black pepper and fat if you want any absorption at all.
• Fresh herbs: stems in water like flowers, bag over the top, in the fridge. Basil on the counter, since it suffers chilling injury. Freeze chopped herbs in oil in ice cube trays.

8. The bottom line

• Herbs and spices are the most chemically concentrated foods you eat and are eaten in the smallest quantities, which is why laboratory findings so rarely translate.
• The evidence that holds up: ginger for nausea (good), enteric-coated peppermint oil for IBS (good), cinnamon for glucose (small and inconsistent), curcumin for osteoarthritis (modest, at supplement doses, with bioavailability problems and reported liver injury).
• Cassia cinnamon contains coumarin at levels where daily supplementation can exceed the tolerable intake. Use Ceylon if you take it regularly.
• Spice adulteration is a real and serious problem, with lead chromate in turmeric the worst documented case. Buy whole, buy reputable, distrust unusually bright colour.
• Their reliable health value is that they make vegetables, pulses, and whole grains worth eating and let you use less salt. That is a bigger effect than any of their pharmacology.

Sources and notes

Essential oil composition and plant family groupings follow standard phytochemistry references. The spice-use-and-climate hypothesis is Billing and Sherman, Quarterly Review of Biology, 1998, with subsequent critiques by Bromham et al. Vanilla hand pollination by Edmond Albius on Reunion in 1841 follows Ecott, Vanilla, 2004. Coriander soapiness and OR6A2 follows Eriksson et al.'s 23andMe genome-wide association study, 2012. Ginger for pregnancy nausea follows Cochrane reviews and ACOG guidance; the mechanism follows Lete and Allue's review. Cinnamon and glycaemic control follows Allen et al.'s meta-analysis with its noted heterogeneity. Coumarin content of cassia versus Ceylon cinnamon and the EFSA tolerable daily intake of 0.1 mg/kg follow EFSA's 2004 and 2008 opinions and BfR warnings. Curcumin bioavailability and its PAINS characterisation follow Nelson et al., Journal of Medicinal Chemistry, 2017; turmeric-associated liver injury follows the LiverTox database and a growing case series. Enteric-coated peppermint oil for IBS follows Cochrane and ACG guideline evidence. Lead chromate adulteration of turmeric follows Forsyth et al.'s Stanford work in Bangladesh, Environmental Research, 2019. Sudan dye recalls follow EU RASFF records. Japanese star anise neurotoxicity follows FDA advisories.

Open questions. Almost every spice health claim rests on doses far above culinary intake, which makes the literature hard to apply. How widespread spice adulteration is in any given supply chain is unknown outside targeted surveys.

👉 That completes the vegetables. Next: grains and bread.