Threonine: Requirement, Indian Food Sources and the Gut Lining

Threonine is one of the nine essential amino acids, which your body cannot make and has to take from food. It goes into ordinary body protein and, in unusually large amounts, into the mucus that coats the gut. An adult needs about 15 mg per kg of body weight a day, and ICMR-NIN's 2020 recommendation is 23 mg of threonine in every gram of dietary protein. Rice protein carries about 33 mg per gram, atta about 26 mg and cow's milk about 48 mg, so a mixed Indian diet usually covers it. This entry is part of the proteins and amino acids section.

What is threonine and what does it do?

Threonine is a building block of protein that only food can supply. ICMR-NIN's Dietary Guidelines for Indians, 2024, explains that nine of the twenty amino acids are not synthesised in the body and are termed essential, and threonine is one of the nine. Every protein your body builds, from muscle to enzymes, draws on it, and when any one essential amino acid runs short the rest cannot be fully used. The article on what protein does in the body covers that general background.

The gut is where threonine stands apart. A study of preterm infants in the American Journal of Clinical Nutrition describes it as abundantly present in the glycoproteins the intestine produces, the mucins that form the protective mucus layer. In those eight infants the intestine took up 70 per cent of dietary threonine on first pass during full feeding and 82 per cent during partial feeding. The authors read this as a high obligatory need of the gut for threonine. It is a finding in infants, not a measurement in adults.

How much threonine do you need?

An adult needs about 15 mg of threonine per kg of body weight a day, by the WHO/FAO/UNU 2007 requirement as printed in the FAO's 2013 report on protein quality. That is about 975 mg for a 65 kg man and 825 mg for a 55 kg woman. The same need is written as a pattern of 23 mg per gram of protein, and ICMR-NIN's 2024 guidelines print 23 mg as the ICMR-NIN 2020 recommendation. The two agree: 0.66 g of protein per kg, each gram carrying 23 mg, comes to about 15 mg per kg.

ICMR-NIN's brief note on its 2020 requirements says the protein requirement should satisfy the amino acid requirements of the 2007 consultation, and sets the adult allowance at 0.83 g of protein per kg a day: 54.0 g for a 65 kg man and 45.7 g for a 55 kg woman. Threonine sits inside that allowance, not on top of it. The note adds 9.5 g of protein a day in the second trimester of pregnancy and 22.0 g in the third. No separate threonine figure for pregnancy or lactation was found in the documents opened for this entry, so none is quoted. The protein calculator gives your own protein figure.

Is threonine really the second limiting amino acid in rice and wheat?

For a young child fed mainly on wheat, yes; for an adult, the Indian food tables say threonine clears the bar. ICMR-NIN's 2024 guidelines list lysine, threonine and tryptophan as the limiting amino acids of cereals and millets. Lysine is the clear first: the handbook's entry on lysine shows atta protein at 24.2 mg per gram against a pattern of 45. Threonine is the next concern, but how short it falls depends on whose pattern you score against.

The Indian Food Composition Tables 2017 give threonine as 2.58 g per 100 g of protein in whole-wheat atta, which is 25.8 mg per gram, and 3.28 g in raw milled rice. Against the adult pattern of 23 mg, atta scores 112 per cent and rice 143 per cent. The FAO's 2013 report recommends a stricter pattern for children from 6 months to 3 years, 31 mg per gram. Against that, atta scores 83 per cent and maida 75 per cent, while rice just passes at 106 per cent.

So the textbook phrase needs a qualifier. In wheat, threonine is the second lowest of the four amino acids the FAO scores in its worked examples, after lysine, and it falls below the pattern only for the youngest children. Rice only just clears the stricter pattern, while ragi and bajra are well above both. The atta page gives the rest of that flour's panel.

Threonine in Indian foods

Milk, paneer, soya bean and rajma are the richest vegetarian sources per gram of protein in IFCT 2017: 48.1 mg in cow's milk, 43.7 in paneer, 38.8 in white soya bean and 41.8 in red rajma. Toor, moong, chana and masoor dal sit close together, between 32 and 34 mg, and groundnut is low at 25.4. The amino acid table in IFCT 2017 covers plant foods, milk and milk products; it gives no profile for egg, meat or fish, so those are not listed here.

The household descriptions are approximate, and the figures are for raw food before cooking. To rank foods by protein alone, use NNWA's table of protein in Indian foods. The rajma page carries that bean's full panel, and rajma chawal puts the best pulse for threonine beside the grain that needs help with lysine.

Too little threonine: who is at risk in India?

Nobody can say with a number, because this entry found no Indian survey that measures threonine status. Risk has to be read from the plate. The people most exposed are those who eat little food overall, and small children whose meals are mostly wheat or maida with little dal or milk, since that is the one common pattern in which the tables show threonine below the reference.

Low protein quality in India is first a lysine problem. A 2018 review in the Indian Journal of Medical Research describes cereals as offering low-quality protein that is limiting in lysine, and cites an analysis in which 4 to 26 per cent of people across age groups were at risk of inadequate quality protein. Threonine was not the measure used. A diet that corrects lysine with pulses and milk raises threonine as well, which is why the two rarely need separate attention.

What does the evidence say?

First, the requirement itself comes from Indian research. In a 2002 study at St John's Medical College, Bangalore, sixteen healthy men were fed six levels of threonine from 7 to 27 mg per kg a day. The breakpoint fell at 15 mg per kg, with a 95 per cent confidence interval of 11 to 27, and the authors concluded that the older international figure of 7 mg was inadequate. The 2018 review records that the 2007 committee used studies of this kind in healthy Indians as its primary data.

Second, the link with gut mucus is real but rests on animals and infants. In a 2005 experiment, rats fed 30 per cent of their threonine requirement for 14 days made mucin more slowly in the duodenum, ileum and colon, while the synthesis of other gut proteins did not change; rats on 60 per cent were no different from controls. Nothing here shows that extra threonine improves gut health in a well-fed adult.

Third, absorption varies by food. The 2018 review tabulates digestibility measured in south Indian adults: 96 per cent for the threonine in whole boiled egg, 94 per cent in chicken meat and 89 per cent in egg white. The FAO's 2013 report, using values predicted from pig data, puts threonine digestibility at 0.86 for wheat and 0.73 for peas, and notes that threonine may be lost to oxidation during processing.

A worked example: a rice-based vegetarian day

This is an illustrative case, not a real person. Take a 34-year-old vegetarian schoolteacher in Chennai who weighs 55 kg. She needs about 825 mg of threonine a day. Suppose her day holds 250 g of raw rice, as idli, rice and curd rice without much curd, and one katori of sambar from 30 g of toor dal. Using IFCT 2017, the rice gives 19.9 g of protein and 651 mg of threonine, and the dal 6.5 g and 212 mg. The total is 863 mg, just above her need.

The same day supplies about 1,135 mg of lysine against a need of about 1,650 mg, and only 26.4 g of protein against an allowance of 45.7 g. Now change the plate: 190 g of rice, 45 g of toor dal, 20 g of moong dal and 300 g of milk. Protein rises to 39.4 g, threonine to about 1,444 mg and lysine to about 2,290 mg. Threonine was never the weak point; fixing protein and lysine carried it along. The sums ignore digestibility.

Common mistakes and myths about threonine

The first mistake is to repeat that rice and wheat lack threonine without asking for whom. On the adult pattern both pass. The second is to treat the three limiting amino acids of cereals as three separate problems needing three fixes, when one katori of dal and a glass of milk answer all of them.

A third mistake is reading the amino acid list on a protein powder as a reason to buy it. ICMR-NIN's 2024 guidelines state that protein powders are unnecessary for normal healthy life and that the amino acid needs can be met from a balanced diet, vegetarian or not. Their non-vegetarian plate supplies 37.8 mg of threonine per gram of protein.

Are threonine supplements safe, and when should you see a doctor?

Short-term safety in healthy men looks acceptable, but there is no established benefit to weigh against it. A 2025 trial gave thirty healthy men 3 to 12 g of L-threonine a day for four weeks and reported no adverse effect up to the highest amount; two of its authors worked for the manufacturer. That is a safety ceiling from one small study, not an intake to aim for, and this entry recommends no dose. No upper limit for threonine was found in the ICMR-NIN documents opened for this entry.

FSSAI's health supplement regulations list L-threonine among the amino acids that may be used. Every pack must carry the words HEALTH SUPPLEMENT, the amount of each nutrient, the warning NOT FOR MEDICINAL USE and a statement that it does not replace a varied diet, and it may not claim to prevent or treat a disease.

See a doctor, not a supplement shelf, for diarrhoea that lasts more than a few days, blood in the stool, unplanned weight loss, or a child who is not growing as expected. Keep taking any prescribed medicine unless your doctor changes it.

Learning about amino acids at NNWA

Amino acid patterns and the reading of IFCT tables are taught at NNWA, a private skill academy based in Kolkata whose classes run online in English and Hindi. They come up in the Diploma in Nutrition and Sports Nutrition courses, which train people to coach healthy clients and to pass medical cases on to a doctor. Neither is a degree or a dietitian qualification.