Oily fish is good for omega-3 and less good for mercury. Wholegrain cereals are good for fibre and less good for cadmium. Rice is the most neutral of cereals and the leading source of inorganic arsenic. The modern diet carries a load of heavy metals that the body clears slowly: mercury is measured in months, cadmium in decades. That is no reason to panic; it is a reason to choose well.
Heavy metals: where they hide
Four metals dominate documented food contamination, each with its own entry point:
- Mercury (methylmercury): fish at the top of the food chain. It concentrates at each step (bioaccumulation) and binds to proteins, so cooking does not remove it.
- Cadmium: cereals (wheat, rice), offal (kidneys, liver), crustaceans, potatoes, and tobacco, since cigarette smoke is the leading non-food source. Half-life in the kidney: 10 to 30 years.
- Lead: old pipework, game shot with lead, certain spices and contaminated soils, old painted toys. Neurotoxic with no known threshold, above all in children.
- Inorganic arsenic: rice and rice products (rice drinks, rice cakes), which draw arsenic from the soil more readily than other cereals.
This contamination is not a one-off scandal: it is the background noise of an agriculture and industry that have dispersed metals into soils and oceans. Chronic low-dose exposure is the real subject, not acute poisoning.
Mercury: the fish hierarchy
Mercury follows the food chain: the bigger, older and more predatory the fish, the more methylmercury it concentrates. The practical hierarchy is straightforward:
- Avoid (high concentration): shark, swordfish, marlin, bigeye and large tunas, pike and wild zander from contaminated waters.
- Limit: albacore and skipjack-type tuna (the common canned tunas), bass, monkfish, carp.
- Favour: sardine, anchovy, mackerel, herring, salmon, trout, small prawns; small fish low on the food chain, rich in omega-3 and low in mercury.
UK and French agency advice for pregnant and breastfeeding women and young children follows this logic: two portions of fish a week, one of them oily, varying the species and avoiding wild predators. The apparent paradox (the recommended fish is also the source of the contaminant) resolves through size: a 30 cm mackerel does not carry the mercury of a 200 kg tuna.
Cadmium and lead: the unsuspected sources
Cadmium enters through cereals (phosphate fertilisers have loaded the soils), offal (a beef kidney concentrates what the animal filtered), crustaceans and shellfish, potatoes, and above all tobacco: smoking doubles to triples the cadmium burden. Its kidney and bone toxicity plays out over decades: cadmium accumulates in the renal cortex and barely leaves.
Lead has left petrol but not old houses (pipes, paint), game (lead shot persists in the meat), and certain farmland near former industrial sites. Children are infinitely more vulnerable: a child’s gut absorbs 40 to 50% of ingested lead against about 10% in adults, and it attacks the developing nervous system.
Liver detoxification: the documented nutritional support
The body does not clear heavy metals quickly, but it does clear them: the liver conjugates, the kidneys filter, the gut excretes. Three documented nutritional strategies support that work:
Crucifers (broccoli, cabbage, cauliflower, rocket): sulforaphane induces phase II liver detoxification enzymes. It is the best-documented food on this terrain.
Sulphur donors (garlic, onion, eggs, crucifers again): glutathione synthesis, the body’s internal chelator, depends on sulphur amino acids. Adequate glutathione is the first internal line against the metal burden.
Competing minerals: iron, zinc, calcium and selenium compete with cadmium and lead for intestinal absorption. Iron deficiency doubles cadmium absorption; that is why children and women of childbearing age, whose ferritin is often low, absorb more. Correcting mineral deficits is a contamination-reduction strategy, not merely nutrition.
Fibre and fermented foods complete the picture: fibre binds part of the metals in the gut lumen and exports them, and a healthy microbiome modulates absorption.
The TCM reading: the Liver that drains and the correct Qi
Chinese dietetics has no word for “heavy metals”, but it has the exact concept of a chronic toxic burden: Du (毒, toxin) taking hold when the Liver can no longer purify. The Liver ensures the free flow of Qi and the “cleanliness” of Blood; an overload of toxins reads in TCM as Damp-Heat gaining the Blood, or Liver Qi stagnation thickening.
The correspondence is practical: the foods that “drain the Liver” in Chinese dietetics (bitters such as endive and artichoke, dark greens, lemon, turmeric) are the same ones documented to induce phase II enzymes. Fatty liver shares this terrain: a congested Liver can no longer purify. And correct Qi (Zheng Qi) describes an organism’s capacity to handle what attacks it, which is precisely what liver detoxification measures.
Frequently asked questions about heavy metals and diet
Should we stop eating fish because of mercury?
No, but choose the species: small fish (sardine, anchovy, mackerel, herring, salmon) supply omega-3 with little mercury. Predators (swordfish, shark, large tunas) are limited. Two portions a week of small fish is the documented balance point.
Is rice dangerous?
Rice concentrates inorganic arsenic more than other cereals. It should not be eliminated but varied: alternate with oats, millet, buckwheat and quinoa, and cook it in a large volume of drained water. Daily rice drinks and rice milks in toddlers are the real point of attention.
How do you know if you are contaminated?
Chronic intoxication is screened by laboratory testing (mercury in hair or blood, urinary cadmium, blood lead), not by symptoms, which are too unspecific. If occupational exposure or a particular context (old house, daily consumption of predatory fish) justifies it, the doctor orders the assays.
Are “metal detox” supplements useful?
No, and they can be dangerous: concentrated chlorella and coriander mobilise metals without eliminating them cleanly, and can redistribute them to sensitive tissues. Documented support comes through diet (crucifers, sulphur, fibre, adequate minerals) and reduced exposure, not capsules.
Choose the prey, not the predator
Heavy metals are the background noise of the modern diet: invisible, slowly accumulating, and managed through everyday choices. Small fish rather than predators, varied grains rather than daily rice, adequate minerals rather than deficiencies that open the door to cadmium. The TCM reading adds its piece: the Liver that drains needs bitters and movement, not overload. Detox is not a diet; it is a permanent hygiene.
In the Yin Shi app, food cards show each product’s omega-3, fibre and mineral content: sardines and broccoli tick the protection boxes, predators the vigilance ones.
To go further: endocrine disruptors and countermeasures, fatty liver as Liver Damp-Heat, the vitamins and minerals guide, the Liver in TCM, and medicinal mushrooms.
To go further
Yin Shi ecosystem resources directly related to this article.