The frequent food questionnaire is considered a reliable research tool that assesses diet quality. However, as with all recorded information, it relies on the subject providing accurate and reliable information. Because of the potential for inaccurate recording, there is a need amongst researchers for a simple and reliable clinical test that accurately predicts the quality of the diet for subjects. One possible test is a urinary potassium measurement. Evidence suggests that foods high in potassium tend to be those recommended for good health, such as fruits, vegetables and beverages such as wine. In contrast, foods that make up the typical Western diet are poor sources of potassium. Therefore, researchers1 have assessed the usefulness of urinary potassium as a marker of diet quality by comparing urine samples to the results of a frequent food questionnaire.
Samples of urine were taken from patients with kidney stones in a lithotripsy unit (aged 18 to 50 y) over a 24 hour period. Each subject completed a frequent food questionnaire, and this was in turn used to derive a recommended food score, which is a measure of the quality of the diet. Subjects also had their blood pressure, heart rate weight and height measured. The results showed that urinary potassium was positively associated with vegetables, fruit, whole grains, low-fat dairy, fish, poultry and wine. In contrast, urinary potassium was negatively associated with red meat, fast food and high-energy drinks. Urinary potassium correlated positively with the recommended food score, but negatively with body mass index, diastolic blood pressure and heart rate. Urinary potassium therefore seems to be a good predictor of a healthy diet and may be a viable alternative to the frequent food questionnaire.
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