Importance: Monoclonal gammopathy of undetermined significance (MGUS), a precursor condition of multiple myeloma, is associated with shorter lifespan and cardiac, renal, neurologic, and immune-related comorbidities. However, there is little known about modifiable risk factors, such as diet, for this condition. Objective: To determine if risk of MGUS is associated with dietary factors in a racially diverse population. Design: Case-control study based on the National Health and Nutrition Examination Survey (1988-2004). Setting: United States population-based study. Participants: 373 individuals whose sera met criteria for MGUS and 1,406 controls, randomly selected from 24,662 potential controls whose sera did not meet criteria for MGUS, matched 4:1 on age, sex, race, body mass index, and NHANES study cycle. Exposures: Diet was characterized by one 24-hour dietary recall, with gram intake of individual foods and beverages aggregated into groups. Unconditional multivariable logistic regressions were used to model associations between intake of several food groups and MGUS, with measures of association reported for the highest relative to the lowest quantile of intake. Main Outcomes and Measures: Odds ratios (OR) and 95% confidence intervals (95% CI) by quantile of gram intake of various food groups of interest. Results: The study included 1,779 participants, 55.0% non-Hispanic White, 57.6% male, with a mean (standard deviation) age of 67.3 (14.2) years. Daily intake of several food and beverage groups were significantly associated with MGUS. MGUS was inversely associated with whole-grain bread, oats, and rice (OR 0.70; 95% CI 0.48-1.00; P<0.05), fruits (excluding juice) and vegetables (OR 0.69; 95% CI 0.52-0.93; P=0.02), vegetables (OR 0.75; 95% CI 0.56-0.99; P<0.05), tomatoes (OR 0.72; 95% CI 0.51-1.00; P<0.05), and cruciferous vegetables (OR 0.44; 95% CI 0.26-0.74; P<0.01). Direct associations were observed for sugar-sweetened beverages (OR 1.34; 95% CI 1.00-1.78; P<0.05), sugar-sweetened soft drinks (OR 1.41; 95% CI 1.01-1.96; P=0.04), and artificially sweetened soft drinks (OR 1.55; 95% CI 1.04-2.33; P=0.03). Conclusions and Relevance: Our study shows that low intake of whole grains, fruits, and vegetables, and high intake of sweetened beverages, are associated with MGUS. The identification of dietary risk factors for MGUS in a diverse population is of direct public health relevance.