Lysine: The Limiting Amino Acid in Cereal-Based Indian Diets

Lysine is one of the nine essential amino acids, the ones your body cannot make and must take from food. It matters in India for a specific reason: cereal protein is short of it, and cereals supply most of the protein in Indian diets. ICMR-NIN's 2020 recommendation is 45 mg of lysine in every gram of dietary protein. Rice protein carries about 37 mg and wheat atta about 24 mg, while dals carry about 61 mg, which is why cereal and pulse eaten together work better than either alone. This entry belongs to the proteins and amino acids section.

What is lysine, and why is it called the limiting amino acid?

Lysine is a building block of protein that has to come from the diet. Your body assembles its own proteins from twenty amino acids, and ICMR-NIN's Dietary Guidelines for Indians, 2024, lists nine of them as essential because they are not synthesised in the body. A food's limiting amino acid is the essential one it supplies least of, measured against what the body needs. Once that one runs short, the others cannot be fully used to build protein.

For grains, that amino acid is lysine. The 2024 guidelines name lysine, threonine and tryptophan as the limiting amino acids of cereals and millets, methionine as the limiting one in pulses, and lysine again in nuts and seeds. The FAO's 2013 report on protein quality calls lysine the amino acid that is often first-limiting in diets. General background is in the article on what protein does in the body.

How much lysine do you need?

An adult needs about 30 mg of lysine per kg of body weight a day, by the WHO/FAO/UNU 2007 requirement as amended in the FAO's 2013 report. For a 65 kg man that is about 1,950 mg, and for a 55 kg woman about 1,650 mg. The same need is more often written as a pattern, and ICMR-NIN's 2020 recommendation, as printed in its 2024 guidelines, is 45 mg of lysine in each gram of protein.

The two forms agree with each other. The average protein requirement used by both bodies is 0.66 g per kg a day, and 0.66 g of protein carrying 45 mg of lysine per gram gives about 30 mg per kg. Children need more for their size. The amino acid chapter of ICMR-NIN's full 2020 report could not be opened for this entry, so the table gives the international values, labelled as such, beside the Indian adult pattern, and quotes no figure for pregnancy or lactation.

These figures sit inside the protein requirement, not on top of it. ICMR-NIN's 2020 report sets the adult protein allowance at 0.83 g per kg a day, 54 g for a 65 kg man and 46 g for a 55 kg woman, and states that the allowance is for quality protein. A footnote adds that for people eating a cereal-based diet with low-quality protein, the requirement is 1 g per kg a day. The protein calculator works out your own figure.

Why are cereal-based Indian diets short of lysine?

Because cereal protein carries roughly half the lysine of pulse or milk protein, and cereals supply most of the protein eaten. The Indian Food Composition Tables 2017 give lysine as grams per 100 g of protein: 3.70 for raw milled rice, 2.42 for whole-wheat atta, 3.19 for bajra, 2.83 for ragi and 2.31 for jowar. Every one of these falls below the pattern of 4.5 g per 100 g of protein, which is the same thing as 45 mg per gram. A diet whose protein comes mostly from roti and rice therefore scores below the pattern, however large the helpings.

A review of national diet surveys in the British Journal of Nutrition found that Indian diets derive almost 60 per cent of their protein from cereals. Intake in sedentary rural, tribal and slum populations was about 1 g per kg a day, which looks adequate until quality is counted with lysine as the first limiting amino acid. On that basis the authors judged that about one third of the sedentary rural population was at risk of not meeting its requirement.

Lysine in Indian foods

Pulses, soya bean, milk and paneer are the vegetarian foods that bring lysine to a cereal meal; ICMR-NIN notes that flesh foods and egg contain all the essential amino acids. In IFCT 2017, toor dal has 6.16 g of lysine per 100 g of protein, moong dal 6.09, masoor dal 6.12, red rajma 6.71, white soya bean 7.18, cow's milk 8.59 and paneer 5.79. Among grains, amaranth seed (rajgira) stands out at 5.45, while groundnut, at 3.39, is no better than rice.

The cereal and pulse portions are close to the raw amounts in ICMR-NIN's sample lunch for a sedentary man, 100 g of cereal and 30 g of pulses; the household descriptions are approximate. For protein content alone, NNWA's table of protein in Indian foods ranks the whole database, and the soya bean page gives that food's full panel. The article on which dal has the most protein compares the dals one by one.

How does combining cereals and pulses fix the gap?

The two foods are short of different amino acids, so each covers the other. ICMR-NIN's 2024 guidelines put it plainly: cereals have lower levels of lysine but higher levels of the sulphur amino acids, methionine and cysteine, and in pulses the reverse is true. Their advice is a combination of cereals with pulses in the ratio of 3 to 1 by raw weight, which they say can meet the requirement for all the essential amino acids. Adding 250 ml of milk a day raises the intake further.

The guidelines also show the result. Their vegetarian My Plate for the Day, with 250 g of cereals and millets, 85 g of pulses and 300 ml of milk or curd, supplies 49.0 mg of lysine per gram of protein against the recommended 45. The non-vegetarian plate supplies 50.0 mg. Dal with rice, idli with sambar and rajma with roti follow the same logic, and a pot of vegetable khichdi with a generous share of dal is the idea in one dish.

Too little lysine: who is at risk in India?

No single disease marks a low lysine intake, and national surveys such as NFHS-5 do not measure it. A 2018 review in the Indian Journal of Medical Research says there is no specific body measurement or functional test that defines a minimum safe intake of an essential amino acid. Risk is therefore estimated from diets. That review cites an analysis in which 4 to 26 per cent of people across age groups in rural and urban India were at risk of an inadequate intake of quality protein, with lysine as the measure.

The people most exposed are those whose plates are nearly all cereal, with little dal and no milk. The same review notes that pulses, milk, egg, fish and meat together contribute less than 36 per cent of protein intake in India. It adds that poor protein quality may be associated with childhood stunting, while warning that it is an overreach to blame protein quality alone.

What does the evidence say?

First, the higher adult requirement rests on Indian research. The 2018 review records that the 2007 WHO/FAO/UNU committee raised the pattern of essential amino acid requirements for adults by two to three times, using as primary evidence balance studies done with stable isotopes in healthy Indian adults. The same work found that intestinal parasites raised the lysine requirement. These were small, carefully controlled experiments.

Second, how much lysine you absorb matters as well as how much you eat. A study in Indian adults, published in the American Journal of Clinical Nutrition in 2019, measured the true ileal digestibility of essential amino acids at 74.6 per cent for chickpea, 71.6 per cent for yellow pea and 63.2 per cent for whole mung bean, rising to 70.9 per cent when the mung was dehulled. Lysine was among the less digestible amino acids in every legume tested.

Third, the FAO's 2013 report works an example with 400 g of wheat, 100 g of peas and 35 g of milk powder: the mixture scores 82 per cent for older children and adults, with lysine as the limiting amino acid. That combining foods raises the score is arithmetic on measured composition; whether it changes health outcomes in adults is far less studied.

A worked example: a vegetarian day before and after

This is an illustrative case, not a real person. Take a 28-year-old vegetarian software engineer in Pune who weighs 65 kg. By the WHO figure he needs about 1,950 mg of lysine a day. On a typical day he eats rotis from 150 g of atta, 150 g of rice and one katori of dal made from 30 g of toor dal, and no milk. Using IFCT 2017, that is 34.3 g of protein carrying about 1,225 mg of lysine: 35.8 mg per gram of protein against the pattern of 45, and about 725 mg short.

Now follow ICMR-NIN's plate: 125 g of atta, 125 g of rice, 45 g of toor dal and 40 g of moong dal, a cereal to pulse ratio of about 3 to 1. Protein rises to 42.5 g and lysine to about 1,870 mg, or 44.1 mg per gram. Add 300 ml of milk or curd, counted here as 300 g, and the day reaches 52.2 g of protein and about 2,710 mg of lysine, 51.9 mg per gram. The sums ignore digestibility, so treat them as a comparison between two days, not a precise intake.

Common mistakes and myths about lysine

The usual mistake is counting grams of protein and stopping there. ICMR-NIN's 2024 guidelines observe that an adult's daily diet often provides 60 g to 70 g of protein, more than is required, and that the real challenge is quality. The second mistake is trusting groundnuts, almonds or seeds to fill the gap, when nuts and seeds are limiting in lysine themselves.

A third mistake is assuming all plant protein digests alike. The guidelines put the digestibility of most vegetarian foods at 70 to 85 per cent, and they estimate that a balanced vegan diet for a moderately active man supplies more than 80 g of crude protein, equal to about 60 g of quality protein. The article on vegetarian protein sources lists the foods to draw on.

Lysine supplements: safety, and when to see a doctor

Most people have no reason to take lysine as a tablet or powder, because food closes the gap. ICMR-NIN's 2020 table of tolerable upper limits has no entry for lysine or any single amino acid; it limits protein as a share of energy instead. The 2024 guidelines advise against high intakes of protein supplement powders and warn that high protein intakes may worsen kidney function in people who already have kidney disease. This entry gives no dose for a lysine supplement.

See a doctor if a child is not growing along the expected curve, if you are losing weight or muscle without trying, or if you have swelling of the feet or face. Do not stop or change a prescribed medicine on the strength of a change in diet.

Learning protein quality at NNWA

Amino acids, protein quality and the planning of vegetarian diets are taught at NNWA, a private skill academy in Kolkata that holds its classes online in English and Hindi. Its courses, the Diploma in Nutrition and Sports Nutrition among them, prepare people to coach healthy clients and to refer medical cases to a doctor. None of them is a degree or a dietitian qualification.