There is global recognition of the impact of malnutrition among adolescent girls on current health, adult health, and the health of subsequent generations. However, there is a dearth of evidence in this area in The Gambia with which to inform effective solutions to this public health issue. The aim of this programme of research was to investigate nutritional status and the individual and wider level determinants among adolescent girls in The Gambia. Three interrelated studies were conducted to address the overall aims. A systematic review (study 1) examined prevalence and determinants of nutritional status among female adolescents in low- and middle-income countries (LMICs). Study 1 revealed multiple determinants (including age, nutrition knowledge, unfavourable eating habits, parental occupation, and setting) of a triple burden of malnutrition (undernutrition, overnutrition and micronutrient deficiencies) among girls in LMICs. The review confirmed the need to conduct primary research among female adolescents in urban and rural Gambia. A pilot study (study 2) involving 32 adolescent girls was conducted. Four focus groups discussions were held to understand views on cultural contexts relevant to nutritional status, optimal recruitment methods, and feasibility and acceptability data collection methods. Questionnaires were administered and physical measures conducted to assess the quality and plausibility of the data obtained (health, diet, physical activity, and nutritional status outcomes, and potential individual and wider-level influences on nutritional status). Findings suggested the main study (Study 3) would be feasible but required mitigation of challenges such as potential refusal to participate linked to fear of injections and distrust of research. Study 3 assessed individual and wider-level influences on nutritional status (including anaemia, weight status, and stunting) defined from anthropometric indices and biomarker measures among 208 adolescent girls. The prevalence of anaemia, underweight, and stunting were 36%, 33%, and 31% respectively, and 26% of participants experienced overweight. Determinants of undernutrition at the individual level included younger age, lack of parasitic worm treatment, and low nutrition awareness. For example, in fully adjusted logistic regression models, the odds of undernutrition (95% confidence intervals) among younger (10-14 years) compared to older (15-19 years) adolescents was 2.44 (1.137 to 5.242); p=0.022. Wider determinants of malnutrition include the availability of electricity, and rural or urban settings. This programme of research identified various individual, household, community, and national level determinants contributing to the triple burden of malnutrition in LMICs, including The Gambia. Adolescence is a critical developmental stage requiring more attention, including targeted nutrition related programmes and policies.