Food allergy is increasingly recognized across geographic regions and age groups, although temporal trends are difficult to separate from differences in diagnostic criteria and surveillance. This narrative review examines how diet and nutrition interact with the wider exposome to influence food allergy risk, oral tolerance, and clinical phenotypes across the lifespan. We critically synthesize evidence on early-life allergen introduction, dietary diversity, fiber and microbial metabolites, Westernized and ultra-processed dietary patterns, epithelial barrier dysfunction, medication exposures, pollution, and changing food systems. Randomized trials support early peanut introduction and, with greater heterogeneity, early egg introduction as preventive approaches; by contrast, causal evidence linking most other nutritional and environmental exposures to clinically confirmed food allergy remains limited. The diet–microbiome–immune axis offers plausible pathways connecting dietary substrates and microbial metabolites to epithelial integrity and immune regulation, but human mechanistic and longitudinal evidence remains incomplete. Globalization, migration, alternative protein sources, and climate-related exposures may reshape allergen encounters. Adult-onset food allergy, pollen–food allergy syndrome, alpha-gal syndrome, and cofactor-dependent reactions further illustrate how environmental influences may alter clinical expression beyond infancy. We propose an integrated life-course framework linking nutritional and non-nutritional exposures, underlying biological pathways, and emerging allergic phenotypes, while explicitly distinguishing intervention-supported findings from observational associations and mechanistic hypotheses. Future studies should combine standardized clinical outcomes with dietary assessment, environmental exposure measurements, functional microbiome profiling, metabolomics, and immune phenotyping to identify modifiable pathways relevant to food allergy prevention.