Gastric cancer ranks among the five most common cancers globally. It holds the third position in cancer-related mortality due to its aggressive nature, metastatic potential, and prevalence of malnutrition among individuals. Malnutrition in gastric cancer patients is primarily linked to inadequate intake of protein and calories, leading to poor postoperative nutritional outcomes. Dietary diversity, which reflects the variety and quality of food consumed, has emerged as a potential strategy to enhance diet quality and improve nutritional status. This narrative review explores the role of dietary diversity in the context of gastric cancer. A structured literature search was conducted using PubMed and the Cochrane Library, targeting open-access, peer-reviewed articles published in English from 1997 to January 2024. The primary search included terms such as “dietary diversity”, “dietary variations”, “food variety”, “food diversity”, “dietary pattern”, “balanced diet”, and “diet quality”. A secondary search focused on terms related to disease outcomes, including “cancer”, “stomach cancer”, “gastric cancer”, “gastrointestinal cancers”, “peptic ulcers”, “morbidity”, and “mortality”. Articles not meeting language, access, or relevance criteria were excluded. The findings suggest that dietary diversity is a significant determinant of overall diet quality and has particular relevance for gastric cancer patients at risk of malnutrition. Despite its importance, limited research has directly examined the impact of diversified diets in gastric cancer contexts. Future collaborative efforts should prioritize preventive strategies and interventions that aim to improve dietary diversity at the individual and population levels. Such measures may improve the nutritional status and clinical outcomes of patients with gastric cancer.