Histidine: Requirement, Indian Food Sources and the Histamine Link

Histidine is one of the nine essential amino acids, which means your body cannot make it and has to take it from the protein you eat. It goes into haemoglobin and many enzymes, and it is the starting material for histamine. ICMR-NIN's 2020 recommendation is 15 mg of histidine in every gram of dietary protein, and the WHO adult requirement is 10 mg per kg of body weight a day. Rice, atta, dals, milk and fish all carry more than 15 mg per gram, so an ordinary Indian diet covers it. This entry is part of the proteins and amino acids section.

What is histidine, and what does it do?

Histidine is a building block of protein with a ring-shaped side chain that can pick up and release hydrogen ions and hold on to metals such as zinc and iron. A 2020 review in the journal Nutrients lists its roles as proton buffering, metal ion chelation, the making of red blood cells and the histamine system. Proteins rich in histidine include the haemoproteins, of which haemoglobin is the best known.

Histamine is formed by removing a carboxyl group from histidine; a review in the Journal of Nutrition places this in cells of the stomach lining, in the mast cells of the immune system and in parts of the brain, where histamine may act as a neurotransmitter. Carnosine, made in muscle from histidine and beta-alanine, appears to work as a buffer and antioxidant. The liver's breakdown of surplus histidine needs folic acid for its last step, which ties it to folate status.

Is histidine essential for adults?

Yes. A feeding experiment settled the matter in 1975. Four healthy men and three men with chronic kidney failure lived in a metabolic unit and ate a histidine-free amino acid diet for about 35 days. Nitrogen balance slowly turned negative, plasma histidine fell by 82 per cent, the haematocrit fell by 25 per cent and five of the seven developed dry, scaly skin.

Everything reversed when histidine was put back. The authors concluded that histidine is essential in adults and that its absence is associated with a failure of normal red cell production. ICMR-NIN's Dietary Guidelines for Indians, 2024, count nine essential amino acids.

How much histidine do you need in India?

An adult needs about 10 mg of histidine per kg of body weight a day, by the WHO/FAO/UNU 2007 requirement as amended in the FAO's 2013 report. That is 650 mg for a 65 kg man and 550 mg for a 55 kg woman, the reference body weights ICMR-NIN uses. Written as a pattern, the figure ICMR-NIN recommended in 2020 and printed in its 2024 guidelines is 15 mg of histidine in each gram of protein.

The two forms describe the same need. Both bodies take the average adult protein requirement as 0.66 g per kg a day, and 0.66 g of protein carrying 15 mg of histidine per gram gives about 10 mg per kg. Children need more for their size. The amino acid chapter of ICMR-NIN's full 2020 report was not opened for this entry, so the table gives the international values by age and no figure for pregnancy or lactation.

Histidine is counted inside your protein requirement, not added to it. ICMR-NIN's 2020 allowance for protein is 0.83 g per kg a day, which comes to 54.0 g for the reference man and 45.7 g for the reference woman, with a note that people on a cereal-based diet of low-quality protein need 1 g per kg. The protein calculator gives your own number.

Histidine in Indian foods

The Indian Food Composition Tables 2017 give histidine as grams per 100 g of protein, and nearly every staple clears the pattern of 1.5. Raw milled rice has 2.45, whole-wheat atta 2.56, ragi 2.37, toor dal 3.16, moong dal 2.55, red rajma 2.70, white soya bean 2.55, cow's milk 2.14 and paneer 2.04. Masoor dal, the lowest of the common dals at 1.93, is still above the line. Sea fish sit highest: mackerel 3.63, sardine 4.31 and hilsa 4.32.

The household descriptions are approximate. The copy of IFCT 2017 read for this entry does not show the essential amino acid row for hen's egg or chicken, so neither appears in the table. For protein alone, NNWA's ranking of protein in Indian foods covers the whole database, and the mackerel page carries that fish's full panel.

Does a vegetarian Indian diet supply enough histidine?

It does, with room to spare. ICMR-NIN's 2024 guidelines work out the amino acid profile of their My Plate for the Day and print it beside the recommendation. The vegetarian plate supplies 24.1 mg of histidine per gram of protein and the non-vegetarian plate 24.8 mg, against the 15 mg recommended. That is about 60 per cent above the target, a wider margin than the same table shows for lysine, where the vegetarian plate reaches 49.0 mg against 45. The cereal and pulse reasoning is in the entry on lysine, the limiting amino acid.

Why can fish rich in histidine cause histamine poisoning?

Because bacteria can turn the free histidine in fish muscle into histamine once the fish is left warm. A joint FAO/WHO expert meeting describes scombrotoxin fish poisoning as the result of eating marine fish such as tuna, mackerel, sardines and anchovy after temperature abuse during or after harvest. The symptoms it lists include flushing, rash, headache, abdominal cramps, diarrhoea, vomiting and a peppery taste or burning in the mouth.

Histamine is heat stable: cooking kills the bacteria but does not remove histamine already formed, so frying or pressure-cooking a badly kept fish does not make it safe. And the meeting set 50 mg of histamine in a meal as the level with no observed adverse effect which, for a 250 g serving, works out to 200 mg per kg of fish. Well-handled fish was reported to stay below 15 mg per kg.

FSSAI regulates this. The Food Safety and Standards (Contaminants, Toxins and Residues) Regulations list the fish species with the potential to cause histamine poisoning, among them Indian mackerel, Indian oil sardine, hilsa, anchovy, seer fish and the tunas. For raw, chilled or frozen fish of these species, nine units are sampled; the acceptable level is 100 mg per kg, no more than two units may fall between 100 and 200, and any unit above 200 rejects the lot. Dried and salted fish, fermented fish and fish pickle are allowed 200 and 400.

Too little histidine: who is at risk?

Almost nobody eating ordinary food. The deficiency in the 1975 experiment came from a purified diet with no histidine at all, which no real diet resembles. National surveys such as NFHS-5 do not measure amino acid intakes. A review in the Journal of Nutrition notes that blood histidine falls in some long-term illnesses, including chronic kidney disease, but that is a finding in patients under medical care and not a reason for a healthy adult to supplement.

What does the evidence say about histidine supplements?

It is thin and early. The best-known trial, published in Diabetologia in 2013, gave 100 obese Chinese women with the metabolic syndrome either histidine or a placebo for 12 weeks; 92 finished. Against placebo, the histidine group showed a lower insulin resistance score, a fall in body mass index of 0.86 and a fall in waist of 2.86 cm. That is one trial in one group of patients, and it says nothing about healthy people of normal weight.

A 2020 review of benefits and adverse effects in the Journal of Nutrition is frank about the limits. It says that it is unclear, from the small number of human studies, whether the changes in blood glucose markers come from histidine itself or from the loss of weight and fat, and that the link between histidine intake and mood, appetite or sleep is ambiguous in humans.

A worked example: a vegetarian day in Coimbatore

This is an illustrative case, not a real person. Picture a vegetarian bank clerk in Coimbatore, aged 41 and weighing 55 kg. At 10 mg per kg she needs about 550 mg of histidine a day. Her day includes rice from 100 g of raw grain, rotis from 100 g of atta, sambar made with 30 g of toor dal, a katori of moong dal from another 30 g, a glass of milk across her coffee and curd, counted as 250 g, and 50 g of paneer.

Using IFCT 2017, the rice gives 194 mg, the atta 271, the toor dal 206, the moong dal 183, the milk 177 and the paneer 193. That is about 1,224 mg of histidine from 49.9 g of protein, or 24.5 mg per gram, more than twice her requirement and close to the 24.1 mg ICMR-NIN reports for its own vegetarian plate. The rice and atta alone, at 465 mg, cover about 85 per cent of her need. The sums ignore digestibility, so read them as a rough check.

Common mistakes and myths about histidine

The first mistake is confusing histidine with histamine. One is an amino acid in every protein food; the other is a signalling chemical your own cells make from it in small amounts. The histamine that causes fish poisoning is made by bacteria in the fish before it reaches the plate.

The second mistake is assuming a vegetarian needs an essential amino acid powder to cover histidine. ICMR-NIN's vegetarian plate supplies 24.1 mg per gram of protein against a recommendation of 15, and the guidelines state that protein powders are unnecessary for normal healthy life. The article on vegetarian protein sources lists the foods that do the work.

Safety: too much histidine and when to see a doctor

No tolerable upper level has been established for histidine, and for supplements the data are short term. In a 2020 trial in the American Journal of Clinical Nutrition, healthy adults took graded amounts of histidine for four weeks. The authors set the level with no observed adverse effect at 8 g a day, because blood measures shifted at 12 g: ferritin was lower, and at 16 g serum zinc fell and a liver enzyme rose, all within normal ranges. That is a ceiling from one short study, not an intake to aim for.

The Journal of Nutrition review adds that intakes above 24 g a day have produced lower serum zinc and impaired thinking, and the Nutrients review judges histidine supplements inappropriate for people with liver disease because of changes in blood ammonia. FSSAI's health supplement regulations list L-histidine among the permitted amino acids, and require every pack to carry the words HEALTH SUPPLEMENT, the warning NOT FOR MEDICINAL USE and a statement not to exceed the recommended daily usage.

After a fish meal, get medical help at once for swelling of the tongue or throat, difficulty breathing, fainting or a racing heart, and see a doctor for flushing, rash, vomiting or diarrhoea that does not settle within a few hours. Do not stop or change a prescribed medicine because of anything you read about an amino acid.

Studying amino acids at NNWA

The essential amino acids, the reading of food composition tables and basic food safety are part of what NNWA teaches. It is a private skill academy in Kolkata with online classes in English and Hindi, and its programmes, including the Diploma in Nutrition and the Certification in Nutrition, train people to guide healthy clients and to send medical cases to a doctor. They are not degrees and do not make anyone a dietitian.