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Thiols, also called mercaptan, are a class of organic chemical compounds, similar to the alcohols and phenols, that contain a sulphydryl group that is composed of a sulphur atom (in place of an oxygen atom) and a hydrogen atom attached to a carbon atom. Some foods that contain sulphur also contain thiols but not all.

Biological thiols are important antioxidants and studies have shown that their contents vary depending on the groups of foods. Thiols are in some vegetables and fruits and include glutathione, N-acetylcysteine, captopril, homocysteine, cysteine, and gamma-glutamyl cysteine.

The thiol contents are between 3-349 nM/g wet weight in vegetables and 4-136 nM/g wet weight in fruits and captopril is only found in asparagus. There are no thiols in apples, blackberries, cabbages, grapes (red) or peaches and very little in other fruits except papaya and pineapples which have high levels of thiols.

Oxidation of these important thiols may occur and result in the production of toxic by-products if they are exposed to radiation and ozone treatment for sterilisation purposes.

Some people develop an intolerance to thiols but are not aware of it and put their symptoms down to other causes.

Symptoms of thiol intolerance

  • Asthma/shortness of breath

  • Brain fog

  • Chronic stress due to elevation of cortisol and glutamate

  • Diarrhoea

  • Fatigue

  • Flushing

  • Headaches

  • High or low blood pressure

  • Hives/itchy skin/eczema

  • Nausea

Anyone planning to chelate heavy metals by consuming sulphur-rich foods should do a thiol exclusion trial at least once to determine if there is a sensitivity to thiols in foods and avoid a lot of suffering.


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It is only food that contains a high level of free thiol groups, and not literally any food that contains elemental sulphur in any form, that need to be avoided when thiol intolerance is suspected.
It is important to keep in mind that limiting sulphur-rich foods should be short-term since the body does need sulphur to make many critical compounds, such as glutathione and taurine. Glutathione is required by the body to eliminate free radicals. A seven-day period of avoiding thiol containing foods is sufficient to establish if they are causing any of the above symptoms. Then introduce those foods back into the diet to determine if they are causing any health issues.

Sulphur food intolerance in mercury toxic people has more to do with the mobilisation of mercury caused by raised cysteine levels and excess thiols, rather than a direct allergy/intolerance to sulphur foods. When cysteine levels are high, foods rich in glutamine and glycine can help to convert excess cysteine into glutathione. Consume one-part glycine rich foods to two-parts of glutamine rich foods.

Natural sources of glycine for those with thiol intolerance

  • Alfalfa

  • Apples

  • Apricots

  • Beef

  • Oily fish

  • Organ meats

  • Poultry

  • Rabbit

  • Venison

Natural sources of glutamine for suitable those with thiol intolerance

  • Beef

  • Beetroot

  • Oily fish

  • Organ meats

  • Parsley

  • Propolis

  • Poultry

  • Venison

The body requires both glutamine and glutamic acid to function correctly.

Natural sources of glutamic acid suitable for those with thiol intolerance

  • Apples

  • Apricots

  • Beef

  • Oily fish

  • Organ meats

  • Poultry

  • Rabbit

  • Venison

Molybdenum is very good at supporting the sulphur pathway which, when functioning optimally, generates glutathione which is the body’s main antioxidant and heavy metal detoxification agent. Molybdenum gets used up quickly in the detoxification of sulphites so extra foods rich in this mineral need to be consumed. Avoiding sulphur-rich foods may lead to a deficiency of molybdenum as the richest sources are beans, nuts and green leafy vegetables.

Natural sources of molybdenum suitable for those with thiol intolerance

  • Barley

  • Bell peppers

  • Carrots

  • Celery

  • Chia seeds

  • Cod

  • Cucumber

  • Lettuce

  • Oats

  • Organ meats

  • Rice (brown)

  • Tomatoes

Vitamin B5 (pantothenic acid) combines with sulphur in the body to make coenzyme A, thus eliminating extra sulphur.

Highest sources of vitamin B5 in milligrams per 100 grams suitable for those with thiol intolerance

  • Brewer’s yeast 13.5 mg (depends upon source)

  • Chicken livers 8.32 mg

  • Rice bran 7.39 mg

  • Sunflower seeds 7.06 mg

  • Whey 5.62mg

  • Yeast extract 4.60 mg

  • Shiitake mushrooms 3.59 mg

  • Fish roe 3.50 mg

  • Spirulina 3.48 mg

  • Paprika 2.51 mg

  • Wheat germ 2.26 mg

  • Sun dried tomatoes 2.09 mg

  • Goose 1.83 mg

  • Lobster 1.67 mg

  • Duck 1.50 mg

  • Peanuts 1.40 mg

  • Buckwheat 1.23 mg

Mercury is known to cause intolerance of thiol-containing foods and can block the methylation cycle causing vitamin B12 deficiency which can lead to concentration difficulties, fatigue and memory impairment. Overcoming methylation dysfunction is aided by limiting both vitamin B9 (folic acid) supplements and foods that are rich in vitamin B9 until the methylation dysfunction is rectified.

Highest sources of vitamin B9 in micrograms per 100 grams

  • Chicken livers 578 µg

  • Basil 310 µg

  • Wheat germ 281 µg

  • Sunflower seeds 238 µg

  • Shiitake mushrooms 163 µg

  • Parsley 152 µg

  • Chestnuts 110 µg

  • Beetroot 109 µg

  • Spearmint 105 µg

  • Fish roe 92 µg

  • Hazelnuts 88 µg

  • Walnuts 88 µg

  • Flaxseeds 87 µg

  • Avocado 81 µg

  • Mussels 76 µg

  • Okra 60 µg

  • Quinoa 42 µg

Highest sources of vitamin B12 in micrograms per 100 grams

  • Clams 98.9 μg

  • Liver 83.1 μg

  • Barley grass juice 80 μg

  • Octopus 36 μg

  • Caviar/fish eggs 20.0 μg

  • Ashitaba powder 17.0 μg

  • Herring 13.7 μg

  • Tuna fish 10.9 μg

  • Crab 10.4 μg

  • Mackerel 8.7 μg

  • Lean grass-fed beef 8.2 μg

  • Rabbit 6 μg

  • Crayfish, pork heart, rainbow trout 5 μg

  • Shiitake mushrooms 4.8 μg

  • Lobster 4 μg

  • Lamb, venison 3.7 μg

  • Salmon 3.2 μg

  • Whey powder 2.37 μg

  • Golden chanterelle mushrooms 2 μg

  • Tuna 1.9 μg

  • Halibut 1.2 μg

  • Chicken, turkey 1.0 μg

  • Ashitaba 0.4 μg

NOTE: One μg is one microgram.

Foods that contain high levels of thiols

  • Alcoholic beverages

  • Artichokes (Jerusalem not globe)

  • Asparagus

  • Bean sprouts

  • Beer

  • Bell peppers (green)

  • Bok choy

  • Broccoli

  • Buckwheat

  • Carob and chocolate

  • Cauliflower

  • Cheese

  • Chickpeas

  • Chives

  • Chlorella

  • Cider

  • Coffee

  • Collard greens

  • Cream

  • Daikon

  • Eggs

  • Garlic

  • Grapes (green)

  • Green beans

  • Horseradish

  • Jicama

  • Kale

  • Leeks

  • Legumes and dried beans and peas

  • Lemonade

  • Lentils

  • Lime/lemon juice (bottled)

  • Milk

  • Miso

  • Mustard

  • Nuts

  • Onions

  • Papaya

  • Peanuts

  • Peas (split and fresh)

  • Pineapple

  • Quinoa

  • Radishes

  • Rocket

  • Sesame seeds

  • Shallots

  • Swede (rutabaga)

  • Soy

  • Spinach

  • Spring onions

  • Tea

  • Tofu

  • Turnips

  • Yoghurt

  • Whey

  • Whisky

  • Wine

  • Yeast extract

NOTE: Turmeric is not high in thiols but has been found to raise levels significantly.

When eliminating thiols from the diet it is important to know that some supplements and medications also contain them or can increase levels of thiol in the blood.

Thiol-containing supplements

  • Alpha lipoic acid (or thioctic acid)

  • Bromelain

  • Chondroitin sulphate

  • Cysteine

  • Dairy sourced acidophilus

  • Dimercaptosuccinic acid

  • Dimercapto-1-propanesulfonic acid

  • Dimethyl-sulfoxide

  • Epsom salts (bath)

  • Garlic

  • Glucosamine sulphate

  • Glutathione

  • Magnesium sulphate

  • Methionine

  • Methylsulfonylmethane

  • Milk thistle

  • N-Acetyl cysteine

  • Papain

  • Sulfonic acid

Sulphur-containing medications (antibiotics, sulfonylurea, etc.)

  • Taurine

  • Food additives high in thiols

  • Sulphur dioxide

  • Sodium sulphite

  • Sodium bisulphite

  • Sodium metabisulphite

  • Potassium bisulphite

  • Potassium metabisulphite

Medications that increase thiol levels

  • Bactrim

  • All diuretics except spironolactone

Foods low in thiols

  • Almond milk

  • Anchovies

  • Artichokes (globe)

  • Aubergine

  • Avocado

  • Bananas

  • Bamboo shoots

  • Barley

  • Basil

  • Beef

  • Beetroot

  • Berries

  • Breadfruit

  • Brown sugar

  • Bulgur wheat

  • Butter

  • Cabbage

  • Caraway seeds

  • Carp

  • Carrots

  • Celery

  • Chicken

  • Chicken livers

  • Cinnamon

  • Clams

  • Coconut (Some coconut products are sulphated to keep them white)

  • Cod liver oil

  • Cottonseed oil

  • Courgettes

  • Cucumber

  • Dates

  • Duck

  • Eel

  • Figs

  • Flounder

  • Fruit (all fruits other than papaya and pineapple are low thiol)

  • Game meat

  • Gelatine

  • Ginger

  • Goose

  • Halibut

  • Hemp seeds

  • Honey

  • Lamb

  • Lettuce

  • Lobster

  • Mackerel

  • Mahi mahi fish

  • Marjoram

  • Mushrooms

  • Oats

  • Octopus

  • Olives and olive oil

  • Oregano

  • Organ meats

  • Oysters

  • Parsley

  • Parsnips

  • Peppercorns

  • Pheasant

  • Pigeon

  • Pork

  • Potatoes

  • Prawns

  • Quail

  • Rabbit

  • Rice

  • Rice milk

  • Rosemary

  • Rye

  • Salmon

  • Sardines

  • Scallops

  • Sea salt

  • Seeds (flax, linseeds, pumpkin and sunflower)

  • Semolina

  • Shark

  • Shellfish

  • Shrimp

  • Smoked fish

  • Snails

  • Soya beans

  • Squashes

  • Sweet corn

  • Sweet potato

  • Thyme

  • Tomatoes

  • Trout

  • Tuna

  • Turkey

  • Vinegar

  • Water chestnuts

  • Watermelon

  • Wheat grass

  • Yams

If there is no improvement to symptoms through elimination of thiols then check that the intolerance is not to the other food allergens listed on this page: Allergies

See also:

"Nature cures not the physician..." Hippocrates 460 BC


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