Lysine is a positive regulator of linear growth, alleviates chronic stress and diarrheal morbidity across different population. Cereals, the major protein source in Indian diet is limiting in lysine. The bioavailability of lysine from a habitually consumed cereal: legume based vegetarian meal is not known. Available estimates of protein quality for mixed diets are based on the inaccurate measures of crude protein bioavailavility. Vegetarianism is usually synonymous with lacto vegetarianism and 34% of the population falls under this category. Milk and milk products accounts for ~ 15% of the total protein intake in rural and urban Indian diets. Milk contains all essential amino acids in adequate amounts, required to meet the needs of the body. However, when milk is subjected to heat treatment and processing lysine undergo degradation (develops modified lysine). Since, modified lysine cannot be absorbed and utilised by the body, processed milk and milk products are likely to be limited in lysine. Therefore, it is important to assess metabolic availability of lysine from milk, heat treated under different conditions. The United Nation expert consultations have introduced a new metric for protein quality evaluation, the Digestible Indispensible Amino Acid Score (DIAAS), which depends on the content and bioavailability estimates of limiting IAA, measured at the level of ileum. However, this requires highly invasive approaches such as, naso-ileal intubation and ileal fistulation. The indicator amino acid oxidation (IAAO) technique is the only bioavailability estimation assay which determines protein quality of mixed diets and other foods in an absolutely non-invasive approach and thus will be used in the present study.