Effects Of Taste Genetics On Food Acceptance


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This presentation details the concept of supertasting and its possible nutritional effects.

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  • Focus of taste genetics will be on bitterness because it has been the most extensively studied taste modality
  • PTC & PROP are members of the thioureas; do not occur naturally in foods Often used interchangeably because of common association of being markers for bitterness perception; PROP is generally used for threshold detection in studies because PTC has a slight smell when used in solutions… TAS2R38 gene has been identified as the gene for PTC sensitivity; three functional single nucleotide polymorphisms within this gene have been found to explain up to 85% of the observed variance in PTC taste sensitivity; some research does show that TAS2r38 polymorphisms aren’t sufficient enough to explain PROP bitterness perception at suprathreshold concentrations suggesting that other genetic or environmental mechanisms might also play a role in PROP taste perception
  • N-C=s group= Thiocyanate moiety Nontasters- Some people cannot taste this chemical at all Tasters- perceive this chemical to be bitter Being a taster has been shown to correlate with a greater general taste acuity, having heightened responses to sweet & salty stimuli and show increased sensitivity to olfactory cues & viscous substances such as fats and food thickeners
  • T2Rs are a family of G protein-coupled taste receptors located at the surface of taste cells as well as palate and epiglottis; Polymorphisms of the genes that code for these receptors are what may explain the variability in taste perception These vegetables usually tend to be nutritionally significant (i.e. spinach, endives and many cruciferous vegetables like broccoli, cabbage, cauliflower, and kale just to name a few) Secondary compounds in these veggies include phytochemicals such as polyphenols, methylxanthines, isoflavones and sulfamides which might protect against certain illnesses
  • do not occur naturally in foods but the variability in response to their taste correlates with taste sensitivity to other bitter substances present in foods
  • Sweetness- different strains of mice used to detect differences in sweet taste perception of saccaharin, to the point where direct evidence for the role of Tas1r3 in saccharin preference came from studies with mice Umami- studies using rats and Chinese hamster ovary cells helped identify genes associated with umami Sour-coexpression of ion channels associated with this modality were first observed in rats Salty- identification of epithelial sodium channels in rodents may have a role in perception of NaCl Research in all these areas are still in their infancy, and though animal research has helped identify possible genes and ion channels, exact mechanisms for these modalities are still unclear. Could be due to fact that bitterness perception and its genetic basis were discovered over 75 years ago through a series of individual responses
  • Relationship between food acceptance and bitterness perception are still being defined
  • Examines the relationship between genetic variation and food acceptance by
  • Subjects tasted room temperature solutions, expectorated and rinsed to ensure that the threshold is roughly halfway between chance and perfect performance Magnitude Estimation with two or more sense modalities create a common scale of sensory magnitude (if a person assigns the same number to two different sensory events, it would mean they have the same sensory magnitude
  • 1. stimuli were randomized within each block and a tone series always followed a taste series
  • using principal component analysis with varimax rotation… Factor analysis with principal component solution can be used to reduce a large set of variables into a few underlying dimensions which can be treated as independent variables. These new dimensions account for the most of the variance of the original set of variables. Forming the food categories was necessary because of the large number of food items. Principal component analysis was based on the use frequencies and same categories were applied to desired use and liking scores as the factor solutions for these ratings were almost identical with those from use frequencies. These factor solutions could explain % of the variation of sweet foods Cronbach's alpha measures how well a set of items (or variables) measures a single dimensional construct; a value of 0.70 or higher is generally considered exceptable
  • The authors felt Ceiling factors are limits that are established not by the intensity of the phenomenon but the measuring instrument; this can inhibit expression of sensory intensity. For example labeled scales have ceilings that force supertasters to give erroneously low ratings
  • Effects Of Taste Genetics On Food Acceptance

    1. 1. Taste Genetics & Food Acceptance Trey Sanders, BSFCS [email_address] October 8, 2009
    2. 2. Outline <ul><li>Taste Genetics </li></ul><ul><ul><li>Underlying mechanisms </li></ul></ul><ul><ul><li>Biomarkers </li></ul></ul><ul><ul><li>Types of cellular & animal studies </li></ul></ul><ul><ul><li>Types of human studies </li></ul></ul><ul><ul><li>Gaps in knowledge </li></ul></ul><ul><li>Taste Disorders </li></ul><ul><ul><li>Who taste disorders affect? </li></ul></ul><ul><ul><li>Diagnosis </li></ul></ul><ul><ul><li>Underlying mechanisms </li></ul></ul><ul><ul><li>Treatments </li></ul></ul><ul><ul><li>Preventions </li></ul></ul>
    3. 3. Outline <ul><li>Food Acceptance </li></ul><ul><ul><li>Definition </li></ul></ul><ul><ul><li>Dietary guidelines & reference intakes </li></ul></ul><ul><ul><li>Health risks & medication interaction </li></ul></ul><ul><ul><li>Gaps in knowledge </li></ul></ul><ul><li>Presentation Paper (Duffy & Bartoshuk, 2000) </li></ul>
    4. 4. Is there a Relationship? <ul><li>Different perceptions of sweetness and bitterness influence consumer’s preferences in foods </li></ul><ul><li>Potentially impacts acceptance of foods that are particularly high or low fat, sweet, or bitter </li></ul>Duffy & Bartoshuk, 2000 ; Mennella et al., 2005
    5. 5. Chemical Forms <ul><li>Phenylthiocarbamide (PTC) </li></ul><ul><ul><li>Chemical involved with bitterness perception </li></ul></ul><ul><li>6- n -propylthiouracil (PROP) </li></ul><ul><ul><li>Chemical relative of PTC </li></ul></ul><ul><li>Varying perception of these chemicals due to a genetic variation </li></ul><ul><ul><li>The bitter receptor TAS2R38 </li></ul></ul>Zhao et al., 2007; The Interactive Library, 1999; Chemical Book, 2007
    6. 6. Taste & Genetics <ul><li>Perceived bitterness stems from the ability to taste compounds that contain a N-C=S group </li></ul><ul><ul><li>i.e. PTC and PROP </li></ul></ul><ul><li>Non-tasters vs. tasters </li></ul><ul><ul><li>Supertasters- a smaller population that has an extreme sensitivity to PROP </li></ul></ul><ul><ul><li>Degree of sensitivity to bitterness is associated with preference of certain sweet or bitter foods </li></ul></ul>Mennella et al., 2005
    7. 7. Taste & Genetics <ul><li>Ability to taste PROP is from a dominant allele, which splits people into three groups: </li></ul><ul><ul><li>Homozygous dominant </li></ul></ul><ul><ul><li>Heterozygous dominant </li></ul></ul><ul><ul><li>Homozygous recessive </li></ul></ul><ul><ul><ul><li>Does not necessarily mean that all people homozygous dominant alleles for PROP are supertasters </li></ul></ul></ul>Basson et al., 2005; Kids Do Science, 2002
    8. 8. Taste & Genetics <ul><li>PROP bitterness correlates with fungiform papillae density </li></ul><ul><ul><li>Structures that hold taste buds </li></ul></ul><ul><ul><li>Anterior 2/3 of tongue </li></ul></ul><ul><ul><li>Supertasters tend to have the highest density of these papillae and taste buds on these papillae </li></ul></ul>Basson et al., 2005
    9. 9. Taste & Genetics <ul><li>Variation in taste sensitivity for bitterness stems from T2R genes </li></ul><ul><li>Receptors involved mainly respond to plant secondary compounds </li></ul><ul><ul><li>Created by plants that are poisonous or undesirable to predators </li></ul></ul><ul><li>Supertasters tend not to like vegetables because they contain bitter secondary compounds </li></ul>Mennella et al., 2005; Garcia-Bailo et al., 2009; Krebs, 2009
    10. 10. Biomarkers <ul><li>Measuring a person’s sensitivity to PTC or PROP </li></ul><ul><ul><li>Defining the degree of sensitivity </li></ul></ul>Zhao et al., 2007
    11. 11. Types of Cellular & Animal Studies <ul><li>Bitterness- not readily available through searches </li></ul><ul><li>Animal studies used in process of other modalities </li></ul><ul><ul><li>Helpful, but not perfect </li></ul></ul>Krebs, 2009; Garcia-Bailo et al., 2009
    12. 12. Types of Human Studies <ul><li>Not able to identify randomized control trial studies </li></ul><ul><li>Other types of human studies: </li></ul><ul><ul><li>Convenience sample (Duffy & Bartoshuk, 2000) </li></ul></ul><ul><ul><li>Sequential cohort (Basson et al., 2005) </li></ul></ul><ul><ul><li>Cross sectional (Zhao et al., 2007, Menella et al., 2005) </li></ul></ul>Krebs, 2009
    13. 13. Gaps in Knowledge <ul><li>Not every part of the population is equally divided into 25% nontasters, 50% tasters, and 25% supertasters </li></ul><ul><ul><li>About 70% tasters and 30% non-tasters in North Americans and Western Europeans </li></ul></ul><ul><ul><li>Trying to understand the genetic variation throughout different populations is still unknown </li></ul></ul>Krebs, 2009; Zhao et al., 2007
    14. 14. Taste Disorders Evergreen Science Center, 2008
    15. 15. What is a Taste Disorder? <ul><li>Involves a variety of conditions including: </li></ul><ul><ul><li>Experiencing phantom perceptions </li></ul></ul><ul><ul><li>Hypogeusia- a reduced ability to taste </li></ul></ul><ul><ul><li>Ageusia- not detecting a taste at all </li></ul></ul><ul><ul><li>System misreading or distorting tastes </li></ul></ul><ul><ul><li>Detecting a bad taste from normally pleasant tasting foods </li></ul></ul>National Institute of Deafness and other Communication Disorders, 2002
    16. 16. Who do Taste Disorders Affect? <ul><li>Birth </li></ul><ul><ul><li>Structure malformation </li></ul></ul><ul><li>After an injury or illness </li></ul><ul><li>Aging </li></ul><ul><ul><li>Taste perception and function decrease </li></ul></ul><ul><li>Prevalence not available </li></ul><ul><ul><li>Varying methods at which conclusions for taste disorders have been drawn </li></ul></ul>National Institute of Deafness and other Communication Disorders, 2002; National Institute of Deafness and other Communication Disorders, 2008
    17. 17. Diagnosis of Taste Disorders <ul><li>Some methods include: </li></ul><ul><ul><li>Determining the lowest concentration of a chemical that a person can recognize </li></ul></ul><ul><ul><li>Asking the patient to compare the tastes of different chemicals </li></ul></ul><ul><ul><li>Asking a patient to note the increasing intensity of a taste when the concentration of the chemical is increased </li></ul></ul>National Institute of Deafness and other Communication Disorders, 2002
    18. 18. Causes of Taste Disorders <ul><li>Some have had since birth </li></ul><ul><li>Other causes include: </li></ul><ul><ul><li>Injury </li></ul></ul><ul><ul><li>Central tumors or lesion </li></ul></ul><ul><ul><li>Dental or oral health issues </li></ul></ul><ul><ul><li>Adverse interactions with medications </li></ul></ul><ul><ul><li>Perception of chemicals associated with certain tastes </li></ul></ul><ul><ul><ul><li>i.e. PTC or PROP for bitterness </li></ul></ul></ul>National Institute of Deafness and other Communication Disorders, 2002; National Institute of Deafness and other Communication Disorders, 2008; Duffy & Bartoshuk, 2000
    19. 19. Underlying Mechanisms <ul><li>Lacking receptor sites for chemicals associated with certain tastes </li></ul><ul><li>Damage to the central nervous system which is directly involved in the innervation of taste bud </li></ul>Duffy & Bartoshuk; National Institute of Deafness and other Communication Disorders, 2008
    20. 20. Treatments <ul><li>Depends on the cause </li></ul><ul><ul><li>Medication: stopping or changing the medication should alleviate the problem </li></ul></ul><ul><ul><li>Also true of some illnesses or allergies; their taste perception returns with recovery </li></ul></ul><ul><ul><li>Correcting a general medical problem </li></ul></ul><ul><ul><li>Occasionally will return spontaneously </li></ul></ul>National Institute of Deafness and other Communication Disorders, 2002
    21. 21. Prevention <ul><li>Practice good oral hygiene </li></ul><ul><li>Have consistent dental appointments </li></ul><ul><li>There is not a preventative measure for taste loss associated with aging </li></ul>National Institutes of Health Senior Health, 2008
    22. 22. Food Acceptance http://www.mychildhealth.net/wp-content/uploads/2009/04/kids-vegetable.jpg
    23. 23. Food Acceptance <ul><li>Evaluation of foods based on their degree of </li></ul><ul><ul><li>Sweetness </li></ul></ul><ul><ul><li>Bitterness </li></ul></ul><ul><ul><li>Overall palatability </li></ul></ul>Duffy & Bartoshuk, 2000
    24. 24. Dietary Guidelines & Reference Intakes <ul><li>Dietary Guidelines for Americans </li></ul><ul><ul><li>Carbohydrates- 45%-65% of total calories </li></ul></ul><ul><ul><li>Fats- 20%-35% of total calories </li></ul></ul><ul><li>Dietary Reference Intakes </li></ul><ul><ul><li>Carbohydrates- 130g/day for males & females ages 1-70 </li></ul></ul><ul><ul><li>Fats not yet been determined </li></ul></ul>United States Department of Agriculture, 2005
    25. 25. Health Risks & Medication Interactions <ul><li>Health risks can include: </li></ul><ul><ul><li>Malnutrition </li></ul></ul><ul><ul><li>Weight inadequacies </li></ul></ul><ul><ul><li>Organ system failure </li></ul></ul><ul><ul><li>Coma </li></ul></ul><ul><ul><li>Death </li></ul></ul><ul><li>Some medications can alter taste acuity </li></ul><ul><ul><li>Could increase difficulty in already picky tasters </li></ul></ul>Mahan & Escott-Stump, 2008
    26. 26. Gaps in Knowledge <ul><li>Frequency of food acceptance was inconsistent throughout the studies </li></ul><ul><li>Status of research based on genetic variation hard to come by </li></ul><ul><ul><li>Earlier studies sometimes did not define levels for tasters </li></ul></ul><ul><li>Prevalent because food acceptance can also be affected by: </li></ul><ul><ul><li>Environmental factors </li></ul></ul><ul><ul><li>Allergies </li></ul></ul><ul><ul><li>Religious preferences </li></ul></ul><ul><ul><li>Dietary preferences </li></ul></ul>Duffy & Bartoshuk, 2000; Zhao et al., 2007
    27. 27. Food Acceptance & Genetic Variation on Taste
    28. 28. Introduction <ul><li>Authors: Valerie B. Duffy, PhD, RD and Linda M. Bartoshuk, PhD. </li></ul><ul><ul><li>Published in the Journal of The American Dietetic Association </li></ul></ul><ul><ul><li>Performed at Yale University in Connecticut </li></ul></ul>Duffy & Bartoshuk, 2000
    29. 29. Background <ul><li>Consumers report that taste is an important factor when selecting foods, though taste is often used as a broad descriptor </li></ul><ul><li>Taste can refer to: </li></ul><ul><ul><li>True Taste - the perception of bitter, sweet, salty, and sour </li></ul></ul><ul><ul><li>Retronasal Olfaction- perception of olfactory stimuli from within the oral cavity </li></ul></ul><ul><ul><li>Oral Somatosensation- perception of touch, temperature, and pain </li></ul></ul>Mennella et al., 2005; Duffy & Bartoshuk, 2000
    30. 30. Background <ul><li>Method of measuring perception is not perfect </li></ul><ul><ul><li>Can be altered by many factors such as hormonal changes and common pathologic conditions </li></ul></ul><ul><ul><li>Authors also use fungiform papillae density because of correlation with bitterness perception </li></ul></ul>Duffy & Bartoshuk, 2000 ; Basson et al., 2005
    31. 31. Research Question <ul><li>Is there a contribution of genetic variation in taste to liking of sweet, fat, and bitter foods and beverages? </li></ul>Duffy & Bartoshuk, 2000
    32. 32. Hypothesis <ul><li>People who taste PROP as exceptionally bitter and have a high density of fungiform papillae have a different oral sensory world from those who taste less PROP bitterness relative to density of fungiform papillae </li></ul><ul><ul><li>Relationship will produce a difference in preference for sweet, fat, or bitter foods and beverages </li></ul></ul>Duffy & Bartoshuk, 2000
    33. 33. Aims of Study <ul><li>Identify a relationship between </li></ul><ul><ul><li>Fungiform papilla density </li></ul></ul><ul><ul><li>PROP bitterness </li></ul></ul><ul><ul><li>Acceptance of foods and beverages with varying bitter, sweet, and fat content </li></ul></ul>Duffy & Bartoshuk, 2000
    34. 34. Methods <ul><li>Convenience sample of 70 healthy adults recruited by advertising in a university community </li></ul><ul><li>Subjects completed a taste related health questionnaire including weight and height for BMI calculation, a food acceptance survey, and the restraint scale </li></ul><ul><ul><li>10 subjects were excluded due to a hearing impairment </li></ul></ul><ul><ul><li>14 subjects were excluded because of high dietary restraint, disinhibition, and weight fluctuation </li></ul></ul><ul><ul><li>Remaining 46 subjects classified as 24 women & 22 men, 8 Asian Americans, 7 African Americans, 24 Caucasians, 6 Latin Americans and 1 Asian Indian </li></ul></ul>Duffy & Bartoshuk, 2000
    35. 35. Research Design <ul><li>Deionized water was used to prepare all PROP and NaCl solutions and served as a rinse before each stimulus </li></ul><ul><li>Threshold testing: two alternative forced choice, up-down detection thresholds </li></ul><ul><ul><li>PROP solutions ranging in quarter log steps from 0.000001 to 0.0032 mol/L </li></ul></ul><ul><ul><li>Concentrations were decreased only after 2 correct choices but were increased after one incorrect choice </li></ul></ul><ul><li>Suprathreshold testing (occurred after threshold testing): subjects used magnitude estimation to indicate intensity of quarter-log steps of solutions and 1,000 Hz tones </li></ul>Duffy & Bartoshuk, 2000
    36. 36. Research Design <ul><li>Subjects asked to rate all stimuli on a common scale of intensity </li></ul><ul><ul><li>PROP solutions were presented after NaCl solutions to prevent context effects </li></ul></ul><ul><ul><li>Subjects then assigned numbers to adjectives: “very strong,” “strong,” “moderate,” “weak,” and “very weak”. </li></ul></ul><ul><ul><li>PROP ratings normalized with the tone ratings that followed the NaCl series </li></ul></ul>Duffy & Bartoshuk, 2000
    37. 37. Research Design <ul><li>For fungiform papillae counts, a methylene blue stain was applied to the anterior portion of the tongue </li></ul><ul><ul><li>Images were recorded through an operating microscope and counted in a 3x3-mm area to the right of the midline at the tongue tip </li></ul></ul><ul><li>Subjects completed an 83-item survey consisting of foods from all major food groups using a hedonic scale </li></ul><ul><ul><li>Instructed to circle “like” or “dislike” for each item and then mark line length on a 200 mm line to indicate the degree of liking or disliking </li></ul></ul>Duffy & Bartoshuk, 2000
    38. 38. Food Liking/Disliking Groups Duffy & Bartoshuk, 2000
    39. 39. Results <ul><li>Data were analyzed with STATISTICA, P < 0.05 </li></ul><ul><li>Perceived bitterness of PROP did not correlate significantly with body weight, height or BMI in either sex </li></ul><ul><li>Fungiform papillae density correlated significantly with BMI in men (r = 0.50) </li></ul>Duffy & Bartoshuk, 2000
    40. 40. Results <ul><li>Based on perceived bitterness of 0.0032 mol/L PROP: </li></ul><ul><ul><li>12 nontasters (5 Women, 7 Men) </li></ul></ul><ul><ul><li>22 medium tasters (10 Women, 12 Men) </li></ul></ul><ul><ul><li>12 supertasters (9 Women, 3 Men) </li></ul></ul><ul><li>Women reported highest perceived bitterness for the 0.0032 mol/L PROP </li></ul>Duffy & Bartoshuk, 2000
    41. 41. Results <ul><li>Fungiform papillae density correlated significantly with perceived bitterness of PROP (P < 0.05) </li></ul><ul><li>Women showed greatest variance in the residuals from the regression analysis of PROP bitterness on funigform papillae density (P < 0.01) </li></ul><ul><ul><li>Significance in funigform papillae density distribution for men was displaced toward lower densities (P < 0.05) </li></ul></ul>Duffy & Bartoshuk, 2000
    42. 42. Results, Table 3 Duffy & Bartoshuk, 2000
    43. 43. Results, continued <ul><li>Perceived bitterness of PROP showed significant correlations with liking of sweets, fruits, and natural sweets </li></ul><ul><ul><li>Negative correlations for women </li></ul></ul><ul><ul><li>Positive correlation for men (just showed significance in fruits) </li></ul></ul><ul><li>Significant negative correlation between liking of sweets and increased PROP bitterness in women </li></ul><ul><li>Women who perceived PROP bitterness did not like fat1, fat2, or cheese significantly </li></ul><ul><ul><li>Men who perceived PROP bitterness significantly liked fat1 </li></ul></ul>Duffy & Bartoshuk, 2000
    44. 44. Results, continued <ul><li>Significant negative correlation between liking of fat and increasing PROP bitterness for women </li></ul><ul><li>Significant positive correlation in men between liking/disliking fat foods and fungiform papillae density </li></ul><ul><li>Neither measure correlated significantly with liking/disliking of bitter beverages or cruciferous vegetables </li></ul><ul><li>Women and men had significant positive correlation between liking/disliking of the vegetable group and fungiform papillae density </li></ul>Duffy & Bartoshuk, 2000
    45. 45. Discussion <ul><li>Authors felt they had </li></ul><ul><ul><li>Better classification of liking/disliking foods to help eliminate the ceiling factor </li></ul></ul><ul><ul><li>Better classification of nontasters, medium tasters, and supertasters </li></ul></ul><ul><li>Associations between PROP bitterness and both sweet & fat preference in women might be related to hormonal variation </li></ul>Duffy & Bartoshuk, 2000
    46. 46. Discussion <ul><li>Fungiform papilla count was from too small of an area to provide a stronger correlation with PROP bitterness </li></ul><ul><li>Impact of taste genetic variation on food acceptance depends on interactions between genetic traits and non-sensory influences </li></ul><ul><ul><li>Could also account for the differences between women and men </li></ul></ul>Duffy & Bartoshuk, 2000
    47. 47. Limitations <ul><li>Small sample size </li></ul><ul><li>Small papillae area count </li></ul><ul><li>Control of non-sensory influences </li></ul><ul><ul><li>Prior associations with certain kinds of foods </li></ul></ul><ul><ul><li>Experimenter bias </li></ul></ul><ul><ul><li>True dietary disinhibition </li></ul></ul>Duffy & Bartoshuk, 2000
    48. 48. Future Recommendations <ul><li>How much other factors play along with genetic variation in determining food acceptance </li></ul><ul><ul><li>Race </li></ul></ul><ul><ul><li>Age </li></ul></ul><ul><ul><li>Sex </li></ul></ul><ul><li>Role of hormones in women’s food acceptance </li></ul><ul><li>Bigger sample size </li></ul><ul><li>Larger area for fungiform papillae counting </li></ul>Duffy & Bartoshuk, 2000 ; Krebs, 2009
    49. 49. Implications for Consumers & Patients <ul><li>Food preferences & patterns may be related to genetic predisposition rather than not understanding healthy eating </li></ul><ul><ul><li>Dietary interventions can ultimately come back to how enjoyable the foods and beverages are despite knowing its health benefits </li></ul></ul><ul><li>Genetic variation is one of many factors that influence oral sensation </li></ul>Duffy & Bartoshuk, 2000
    50. 50. Questions?
    51. 51. Q&A <ul><li>What were the genetic markers used to assess taste? Perceiving of PROP bitterness and Fungiform Papillae density </li></ul><ul><li>In Table 3, what category had opposite correlation significance for women and men? Fruits; Negative correlation for women and Positive Correlation for Men </li></ul><ul><li>Which sex showed a significant negative correlation between PROP bitterness and liking of sweets? Women </li></ul><ul><li>Which category showed a significant positive correlation with fungiform papillae density in men? Fat Average </li></ul>
    52. 52. References <ul><li>Basson MD, Bartoshuk LM, Dichello SZ, Panzini L, Weiffenbach JM, Duffy VB. Association between 6-n-propylthiouracil (PROP) bitterness and colonic neoplasms. Dig Dis Sci. 2005(50):483-9. </li></ul><ul><li>Chemical Book. 2007. Propylthiouracil Product Description. Retrieved September 30, 2009 from www.chemicalbook.com/CAS%5CGIF%5C51-52-5.gif </li></ul><ul><li>Duffy VB, Bartoshuk LM. Food acceptance and genetic variation in taste. JADA. 2000;100(6):647-55. </li></ul><ul><li>Evergreen Sinus Center. 2008. Smell and Taste. Retrieved October 2, 2009 from http://www.evergreensinus.com/condition-smell-taste-evergreen-sinus-center-kirkland-washington.htm </li></ul><ul><li>Garcia-Bailo B, Toguri C, Eny KM, El-Sohemy A. Genetic variation in taste and its influence on food selection. OMICS. 2009 Feb;13(1):69-80. Review </li></ul><ul><li>Kids Do Science. 2002. Genetic Puppets. Retrieved October 2, 2009 from http://www.uga.edu/srel/kidsdoscience/kidsdoscience-genetics-puppets.htm </li></ul>
    53. 53. References <ul><li>Krebs JR. The gourmet ape: evolution and human food preferences. Am J Clin Nutr. 2009 Sep;90(3):707S-711S. </li></ul><ul><li>Lahteenmaki L, Tuorila H. Three-factor eating questionnaire and the use and liking of sweet and fat among dieters. Physiol Behav. 1995; 57:81-88. </li></ul><ul><li>Mahan, L.K., & Escott-Stump, S. (2008).  Krause’s Food & Nutrition Therapy .  St. Louis: Saunders Elsevier.  </li></ul><ul><li>Mennella JA, Pepino Y, Reed DR. Genetic and environmental determinants of bitter perception and sweet preferences. Pediatrics. 2005;115(2):E216–222. </li></ul><ul><li>My Child Health. How to get kids to eat their vegetables. Retrieved October 2, 2009 from http://www.mychildhealth.net/wp-content/uploads/2009/04/kids-vegetable.jpg </li></ul><ul><li>National Institute of Deafness and other Communication Disorders. 2002. Internet. http:// www.nidcd.nih.gov/health/smelltaste/taste.asp (accessed 26 August 2009). </li></ul>
    54. 54. References <ul><li>National Institute of Deafness and other Communication Disorders. 2008. Internet. http:// www.nidcd.nih.gov/health/statistics/taste.asp (accessed 26 August 2009). </li></ul><ul><li>National Institutes of Health Senior Health. 2008. Internet. http://nihseniorhealth.gov/problemswithtaste/causesandprevention/08.html (accessed 26 August 2009). </li></ul><ul><li>The Interactive Library. 1999. Interactive Molecules: Phenylthiocarbamide. Retrieved September 30, 2009 from http://www.edinformatics.com/interactive_molecules/3D/ptc_molecule.htm </li></ul><ul><li>United States Department of Agriculture. 2005. Dietary Reference Intakes: Macronutrients. Internet. http://www.iom.edu/Object.File/Master/7/300/Webtablemacro.pdf (accessed September 2, 2009).  </li></ul><ul><li>Zhao L, Tepper BJ. Perception and acceptance of selected high-intensity sweeteners and blends in model soft drinks by propylthiouracil (PROP) non-tasters and super-tasters. Food Quality and Preference. 2007;18(3):531-40. </li></ul>