6-n-propylthiouracil: Orosensory influence on taste, diet, and chronic disease risk

Taste sensitivity to 6-n-propylthiouracil (PROP) is genetically determined and purported to influence diet selection though a direct effect on taste perceptions and food preferences. Studies suggest that PROP tasters, due to higher taste bud and fungiform papillae densities, are more sensitive to the bitterness of fruits and vegetables and fat in foods, and thus have lower food preferences for and intake of fruits, vegetables, and fat, than nontasters. Consequently, it has been posited that PROP taster status may serve as a genetic taste marker to identify individuals at increased risk for developing diet-related chronic diseases, such as obesity, cancer, and cardiovascular disease. This study took a comprehensive approach to investigating this proposal by measuring differences in orosensory responses to fat, diet selection, body composition, and serum lipids within a study population balanced for PROP taste sensitivity and gender. Fungiform papillae density, tactile acuity, and capsaicin sensitivity were also measured, and methodological issues surrounding current measurement and classification methods for determining PROP taster status were evaluated. Healthy young adults (34 men; 36 women) were classified into three PROP taster groups (nontasters, medium tasters, and supertasters) and participated in 20 test sessions during this 16-week study. PROP sensitivity was measured using four measurement methods (paper-disk, 1-, 3-, and 5-solutions of PROP and sodium chloride, NaCl), in duplicate trials, with stimuli randomly presented and nostrils blocked. Taste and fat intensity of three free fatty acids (oleic, linoleic, and stearic) in five concentrations, and fat intensity of and pleasantness for dietary fat in fat-free, reduced-fat, and regular fat versions of six commercially available foods and in five concentrations of six laboratory prepared food systems were measured. Fat stimuli were randomly presented, in duplicate, within and across subjects, with free fatty acids presented using procedures to minimize textural, visual, and olfactory cues for detecting fat. Dietary intake was measured using food frequency questionnaires and 24-hour multiple-pass recalls. A 12-week nutrition intervention focused on increasing fruits and vegetables and decreasing fat consumption was included to investigate whether PROP taste sensitivity is a barrier to adopting healthier eating habits. Body composition, heights, weights, and fasting serum lipids were measured at baseline. Analysis of 130 possible measurement/classification method combinations per trial revealed that no combination was 100% reliable, and that classification consistencies between ten published PROP taster status protocols were low, supporting this study\u27s approach of using the same PROP taster groups to investigate the relationship between PROP sensitivity and risk factors of diet-related chronic diseases. There were no differences observed between PROP taster groups in orosensory responses to fat, intake of fruits, vegetables, and dietary fat, adiposity, body mass indices, serum cholesterol, low-density lipoproteins, or triglyceride concentrations. PROP taster status was not a barrier to medium tasters and supertasters consuming more fruits and vegetables, and nontasters consuming less dietary fat. There was no association between fat intensity and pleasantness ratings in foods, however fat intensity ratings increased across concentration gradations in free fatty acid model solutions and in laboratory prepared food systems consistent with a view that fat may be a sixth primary taste. Fungiform papillae densities, tactile acuity, and capsaicin sensitivity also did not differ among PROP taster groups. Collectively, these findings do not support the proposal that PROP taster status is a genetic taste marker to identify individuals at risk for developing diet-related chronic diseases, and suggest that PROP sensitivity is not a factor warranting consideration when developing menus, recipes, food products, or nutritional counseling and behavioral intervention strategies aimed at increasing fruits and vegetables, or decreasing dietary fat consumption