The study will be implemented in collaboration with BRAC (Bangladesh Rural Advancement Committee) is one of the top-ranked most effective multinational non-government organization (NGO) in the world- headquarter based in Dhaka, Bangladesh. Among many development programmes, BRAC has a specific programme for adolescents- named 'BRAC Adolescent Development Programme' which formed adolescent clubs as a part of their project. These clubs targeted all adolescent girls in the community regardless of their school attendance, marital status, pregnancy, or socio-economic status. The clubs provide a unique place and opportunity for adolescents to socialize both in rural and urban settings. Each club comprises of 25-40 adolescents, mainly girls and a few boys member between ages 10 to 19 years. These clubs operate in afternoons in BRAC schools, while in the absence of such facilities, a room is rented locally by BRAC.The efficacy study will be conducted at the BRAC's Adolescent Clubs. The adolescent Clubs will be selected from 4 Upazilas i.e., Muktagacha, Nanadail or Mymensingh Sadar (Central), Bhaluka, Gaffargaon of Mymensingh district in Bangladesh. There will be three lentils based dietary intervention arm in this efficacy trial. Arm 1 will be intervened with iron-fortified lentils, the 2nd arm will be non-iron fortified lentils, and 3rd arm will be the usual intake of lentil (no additional lentil). Arm 2 will be served as a comparison group and arm 3 will be served as control group. Considering the lower estimation on the expected difference in mean serum ferritin (5mgm/L) with 80% power at 0.05 significance level, Intra Cluster Correlation (ICC) 0.025, a total of 59 cluster will be selected (each club will be treated as a cluster) where a total of 11 eligible adolescent girls will be selected from each cluster. A total of 335 adolescent girls will be placed in each of the intervention arms. The sample size was further incremented to minimize 20% lost to follow-up (resulting 420 in total) during the intervention period of 85 feeding days (approx. 4 months). Thus, the total sample size would be 1252 adolescent girls. A total of 20 adolescent clubs (420 adolescent girls - including 20% drop-outs) will be included in each arm - a total of 1252 adolescent girls in three arms. Participating adolescents will be served thick preparation of cooked lentils (37.5gm raw lentil) 5 days a week for 85 feeding days (around 4+months). In a typical week, the BRAC adolescent club run for 2 days a week (Thursday and any other day). As this study proposes to serve daal 5 days a week, the research team will invite participants to visit the clubs for extra 3 days and consume the cooked lentil/daal. BRAC field level staff will encourage adolescent girls to come to clubs and also their parent to allow them to join the club for consuming dal. These adolescent girls reside in the area near the clubs. The researchers, therefore, assume that there will be full participation in non-club days.

All adolescent girls will be enrolled in the study, will be tested for parasites and be de-wormed prior data collection. Baseline, midpoint and endpoint data collection will include venous blood samples to measure Fe status, anthropometry, and cognitive outcomes. Each of the survey (baseline and endline) survey would take around 30 min per participants. However, in the midline, only venous blood samples will be collected to measure body iron status. Fe status measurement will include hemoglobin, hematocrit (volume of red blood cells), serum ferritin, soluble transferrin receptor (sTfR), C-reactive protein and imputed total body Fe (Aim 1). Height, weight, mid-upper arm circumference (MUAC), and total serum ferritin (TSF) of adolescents will be measured regularly (Baseline and endline) during the study to determine the change in growth. Ravens Progressive Matrices (RPM) and Cambridge Neuropsychological Test Automated Battery (CANTAB) assessments will be used for non-verbal measurement of the cognitive ability of advanced observation and thinking skills specific to capacity for analyzing and solving problems, abstract reasoning, and the ability to learn. Two rounds of data collection in the baseline and endline will include information on socio-demographic characteristics, household food security status, and adolescent food habits (FFQ). Periodic data collection will be carried out in order to track the smooth intervention with defined intervals (every month) on the compliance of the respondents, participants' morbidity including parasitic infestation, menstruation, fortified lentil distribution efficiency, fortified lentil stock, and other explanatory variables. Process evaluation of intervention performance will be conducted in a selected number of adolescent clubs to understand if the interventions are implemented as planned. The process evaluation will provide information related to intervention impact pathway and immediate feedback to the project implementers. In addition, it will help to interpret the research findings. A venous blood sample (approx. 10ml) will then be collected by a well-trained phlebotomist from each of the participants using lithium heparinized vacutainer following aseptic procedure and using disposable syringe and needle. Vacutainers will be carried to the nearest field laboratory in an ice box for serum separation and which will then be stored at 2-8 degree Celsius (°C). All plasma samples will be shipped to central laboratory of International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B) based in Dhaka within 72 hours of collection where the samples will be analyzed. The blood collection per participants will take around 10 min.