The Effect of Lemonade and Diet Lemonade Upon Urinary Parameters Affecting Calcium Urinary Stone Formation.

PURPOSE: To determine the effects of regular and diet lemonade upon urinary parameters affecting kidney stone formation. METHODS: In this prospective blinded crossover study, 12 healthy participants consumed either 2 L of regular or diet lemonade daily while on a standardized low sodium moderate calcium diet. Twenty four-hour urine collections were obtained at baseline on the controlled diet only and on days 4 and 5 of each treatment phase. There was a 1-week washout period between regular and diet lemonade treatments. Primary outcomes were urine citrate, pH, and volume determined by 24-hour urine collections. Secondary outcomes included the supersaturation of calcium oxalate, calcium phosphate, and uric acid. RESULTS: Urine volume was significantly higher with both regular and diet lemonade consumption compared with baseline values. Urinary citrate significantly increased from baseline with diet lemonade only. Urine pH was unchanged with both beverages. The supersaturation of calcium oxalate significantly decreased with diet lemonade only, whereas supersaturation of calcium phosphate decreased with both beverages. Daily consumption of 2 L of regular and diet lemonade resulted in an intake of 168.4 and 170.2 mEq of citrate but a total alkali intake of 12.2 and 16.0 mEq, respectively. Compared with diet lemonade, regular lemonade provided subjects with 805 additional calories and 225 g of sugar per day. CONCLUSIONS: Diet lemonade may provide a low-calorie sugar-free cost-effective option for decreasing the risk of recurrent calcium nephrolithiasis through a significant increase in urine volume, increase in urinary citrate, and reduction in supersaturation of calcium oxalate and calcium phosphate.

Psychosocial predictors of healthful dietary behavior in adolescents.

OBJECTIVE: To identify predictors of healthful dietary practices in adolescents using the Theory of Planned Behavior and determine how gender and ethnicity influence the relationship among the theoretical constructs. DESIGN: Initial and 1-month follow-up questionnaires, designed to measure the constructs of the Theory of Planned Behavior and select demographic items, were administered to the participants in the spring of 1997 to gather data for this descriptive research. SETTINGS/PARTICIPANTS: A sample of 780 adolescents, aged 14 to 19 years, was recruited from randomly selected science classes at 4 public high schools in San Bernardino, California. Seven hundred and fifty participants (96%) completed the initial questionnaire and 672 (86%) completed the follow-up questionnaire. ANALYSIS: A 5-step hierarchical multiple regression procedure, general linear model analysis, and Tukey's honestly significant difference post hoc test were used to analyze the data. RESULTS: Intention to eat a healthful diet was a predictor of healthful dietary behavior. Intention was influenced most by attitude and then by perceived behavioral control and subjective norm. Those with positive attitudes toward healthful eating believed that they would like the taste of healthful foods, feel good about themselves, tolerate giving up foods that they like to eat, and lose weight or maintain a healthful weight. Mother, siblings, and friends were identified as important predictors of subjective norm. Knowledge about how to eat a healthful diet, availability of healthful foods, motivation, and access to enough money were salient facilitating factors related to perceived behavioral control. Interesting contrasts among gender and ethnic groups also were noted. CONCLUSIONS AND IMPLICATIONS: The findings indicate that multiple attitudinal, normative, and control factors influence healthful dietary behavior in adolescents. The synergistic use of these factors in the development and implementation of nutrition education interventions may assist in the promotion of healthful eating among teens from culturally diverse communities.