The Healthy Eating Index-2010 is a measure of diet quality as portrayed by the Dietary Guidelines for Americans; however, computing the Healthy Eating Index score is time consuming and requires trained personnel. The Rapid Eating Assessment for Participants [shortened version] is a simple measure that quickly, in less than 10 min, assesses diet quality in a clinical or research setting. This research evaluated the degree of correlation between these two methods of scoring diet quality, as well as between these methods and other indicators of diet quality, including the nutrient density of the diet, the dietary potential renal acid load, urine pH, and plasma vitamin C concentrations. The research design was a secondary data analysis, and participants were healthy adults (n = 81) self-classified as omnivorous, vegetarian, or vegan. Confounding variables were identified and controlled using partial correlations. The two methods of scoring diet quality were significantly correlated (r = 0.227, p = 0.047). Both the Healthy Eating Index and the Rapid Eating Assessment for Participants scoring methods were correlated to nutrient density of the diets (r = 0.474 and r = 0.472 respectively, p < 0.001) as well as to the dietary potential renal acid load and urinary pH (r ranging from 0.304-0.341, p ≤ 0.002). The Rapid Eating Assessment for Participants, but not the Healthy Eating Index, was significantly correlated to plasma vitamin C concentrations (r = 0.500, p < 0.001 and 0.192, p = 0.095 respectively). These results in combination with ease of use and low cost suggest that the Rapid Eating Assessment for Participants measure is a useful tool for assessing diet quality.