Understanding the economic costs attributable to unhealthy diets is crucial to inform health and agrifood investments in low- and middle-income countries experiencing nutrition transition. To review the current evidence on the association between diet quality and economic costs in low- and middle-income countries, this paper first conducted a literature search to identify studies that include a dietary exposure, nutrition, or health outcome, and a cost estimate. Given the limited studies in terms of life stage groups represented, a second search was conducted for systematic reviews and meta-analyses of observational studies, with effect size estimates for the risk of nutrition or health outcomes associated with diet quality. Of 21 studies (search 1), most were based on the Global Burden of Disease model and estimated the fraction of diet-related noncommunicable disease outcomes attributable to individual or groups of dietary risk factors. The search found 82 systematic reviews and meta-analyses (search 2) that estimated the burden of malnutrition associated with dietary risk factors. Low dietary diversity was associated with increased risk of undernutrition and anemia in pregnant women and children. Dairy consumption was protective for low birthweight, child obesity, and diabetes and hypertension. Low animal source food intake increased the risk of anemia and zinc deficiency during pregnancy. Unhealthy food consumption, including ultra-processed foods and sugar-sweetened beverages, increased the risk of overweight/obesity, diabetes, and hypertension. Healthy dietary patterns were protective during pregnancy for maternal and birth outcomes, and for diabetes and hypertension in adults. The results highlight gaps in quantifying the contribution of diet quality to multiple forms of malnutrition and noncommunicable diseases.