announcement Important for the exam
The exam will be computer graded. You MUST bring a #2 pencil (preferably one with an eraser) or you will not be able to fill out an answer sheet. I will have some pencils, without erasers, available on a first come, firstserved basis.
Lecture 13
How flexible are our eating habits? Instinct vs. learning in food choice Biology of taste preferences
Recommendations of American Psychological Association Task Force on Advertising and Children (2004) * Restrict advertising primarily directed to young children of eight years and under.
Policymakers need to take steps to better protect young children from exposure to advertising because of the inherent unfairness of advertising to audiences who lack the capability to evaluate biased sources of information found in television commercials.
* Investigate how young children comprehend and are influenced by advertising in new interactive media environments such as the internet. * Examine the influence of advertising directed to children in the school and classroom.
Such advertising may exert more powerful influence because of greater attention to the message or because of an implicit endorsement effect associated with advertising viewed in the school setting.
Advertising to Youth
Vulnerability at age of susceptibility to formation of taste preferences and addictions
Approximately eight out of ten of adult smokers started smoking when they were adolescents (Centers for Disease Control, 2004). Nicotine addiction is more likely to occur when first use occurs at a young age (Substance Abuse and Mental Health Services Administration, 2004).
Can our food preferences be imprinted like our social behaviors?
"Flavor programming" in infants:
Preference for dairy vs. protein hydrolysate-based formula (Nutramigen) is shaped over 7 weeks' exposure
Can Taste Preferences be Learned in the Womb?
J.A. Menella et al. 2001
Pregnant women given water or carrot juice to drink (300 ml/day, 4 days/week) during last trimester and/or first 2 mo. of nursing Carrot flavor is distinct and known (like garlic, anise) to be transmitted to human milk Determine whether infant's hedonic response to carrot-flavored cereal is influenced by preor postnatal exposure to the flavor
Pre- and post-natal exposure shapes infants' tastes
Mennella, J. A. et al. Pediatrics 2001;107:e88
Copyright 2001 American Academy of Pediatrics
Preferences formed in infancy last into adulthood
R. Haller et al. Chemical Senses 1999 Vanilla was commonly added to infant formula in Germany for many years 133 Adult Germans were offered ketchup to taste 0.5g vanilla/kg added to one ketchup choice (too dilute to be recognized as added taste)
Preference
Breast Fed (n=103) Pure ketchup 73 (70.9%) Vanilla Added
P<0.01
Bottle fed (n=30) 10 (33.3%) 20 (66.7%)
30 (29.1%)
Breast feeding of infant significantly increased preference for vanilla
Salt Hunger is not learned
Removal of adrenal cortex leads to fatal loss of body sodium Rats will increase salt intake if it is available sufficient to stay alive after adrenalectomy Adrenal hormones stimulate salt appetite Specific hunger for calcium also exists regulated by parathyroid glands
An innate specific hunger for salt is present before weaning
Effect of sodium balance on salt hunger in the preweaned rat. Intakes of water and 3% NaCl by 22-day-old rat pups on liquid saturated towels in an incubator. Black bars, control pups; shaded bars, sodium-depleted pups, *P < 0.001. Regardless of prior sodium intake, all pups ingesting water lose weight, whereas only sodium-depleted animals drink sufficiently to gain weight.
A case of human salt hunger
Richter was also always on the alert to see clinical analogues for his experimental work on behavioral adaptations. For example, as mentioned above, a young boy had been admitted to Hopkins because of marked development of secondary sex organs. In the hospital they made a fatal mistake. They placed the boy on a regular hospital diet, low in sodium chloride. The boy subsequently died. At autopsy it was discovered that he suffered from adrenal cortical pathology. Therefore, he could not produce aldosterone, the principle mineralocorticoid, and was unable to retain sodium. It turned out, in interviews with the parents, that the boy loved salt, ate pure salty foods; salt was one of his first words. The excessive salt ingestion of the boy was a behavioral adaptation to insure the regulation of the internal mileu, just as it was in the adrenalectomized rat.
Pica: Ingestion of non-food substances
Craving may be for coal, soil, chalk, paper, etc. Some consider compulsive eating of inappropriate food items (flour, raw potato, starch) considered pica Incidence may rise in pregnancy Often associated iron with deficiency Lead pica, especially in children, can lead to mental retardation
Hundreds of coins found in patient's belly
Wednesday, February 18, 2004 BOSTON, Massachusetts (AP) -- French doctors were taken aback when they discovered the reason for a patient's sore, swollen belly: He had swallowed around 350 coins -- $650 worth -along with assorted necklaces and needles. The 62-year-old man came to the emergency room of Cholet General Hospital in western France in 2002. He had a history of major psychiatric illness, was suffering from stomach pain, and could not eat or move his bowels.
An X-ray shows the patient's stomach filled with coins, necklaces and needles
Food aversions can be Classically conditioned The Garcia effect: taste specifically salient as a cue Ability to link taste with illness over long intervals Aversions difficult to extinguish
Taste aversion learning in Humans
Bernstein Science 200:1302-3, 1978
Experimental Subjects:
Children ages 2-16 receiving toxic chemotherapy (induces nausea)
Control groups:
Given GI toxic drug but no novel taste received chemotherapeutic drugs that do not induce nausea Given maple/black walnut ice cream 15-60 min before therapy Patients had experienced 23 prior treatments and were aware they induced nausea Offered ice cream again 2 days later Aversion to Mapeltoff vs. other novel flavors persists in experimental group for at least 4 months; controls don't avoid Mapletoff
Neophobia: Are children "picky eaters?" Child food neophobia scale shows not all foods are avoided equally Age and gender do not correlate with neophobia Sweet, fatty snack foods and starchy staples were less likely to be avoided Parental intake (except perhaps for eggs) doesn't predict neophobia
What properties of food determine what and how much we eat and our resulting health?
Preference for sweet solutions
Hedonic optimum (breakpoint) for sweet solution is around 9% wt/volume in adults Children do not show breakpoint - preference continues to rise as sweetness increases Obese people less likely to reduce preference for sweets after consuming sweet solution Sensory responses to sweetness nevertheless differ among the obese; sweetness preference doesn't correlate with body weight Preferences for degrees of sweetness doesn't correlate with overweight among consumers
Some bioactive plant compounds (alkaloids and glycosides) tend to be bitter and to predict toxicity
Phytoestrogens in berries Indoles and isothiocyanates in cruciferous vegetablies Bioactive flavenoids in citrus, onions, kale
Rejection of Bitter Tastes
Sensitivity to some bitter tastes (propylthiouracil) appears heritable and may correlate with taste bud morphology PROP tasters more likely to avoid cabbage, brussels sprouts, spinach, kale, rhubarb, sauerkraut, beer, coffee Children are more likely to reject bitter, and select sweet tastes Genetic taste markers may be early indicators or risk factors for diet-related diseases
Taste and other Sensory Systems
Figure 10-4: Sensory pathways
Fat appetite
First sensory response to fat is via nose and mouth: response to fat-soluble volatile flavor molecules Dairy fat has emulsified globules that are "smooth and creamy". Juiciness of steaks, moistness of cakes due to water-binding in fats Heat transfer affects textures: crispy, crunchy or brittle Hedonic response to sweetness is potentiated by fat Peak hedonic response is to mixtures containing 20%fat wt/wt and 8% sucrose wt/wt Obese women select less sweet, but higher fat stimuli than normal weight women Preference for higher fat food is correlated with subjects own % body fat Preference for a consumption of fat in 3-5 yr old children correlates with parents' BMI: familial and/or genetic component?
Neurotransmitters in Cravings and Hedonic responses
Opiate peptides may play a role in pleasure response to sweet and fat
Agonists and antagonists affect perceived pleasantness of sweet solutions and consumption of preferred foods Binge eating in obesity and bulimia reduced by naloxone, an opiate antagonist Opiate withdrawal reportedly eased by ice cream and chocolate Alcohol cravings mediated by opiate peptides; naltrexone (antagonist) used in treatment
Arguments for link of cravings to serotonergic neurons
Plant compounds can occupy Receptors for endogenous Opiate peptides
Summary
Some taste preferences can be learned in infancy or even earlier Some taste preferences (specific hungers) are innate Genetic differences exist in sensitivity to some tastes Taste aversions can be formed by classical conditioning through nausea Hedonic properties of food are detected by taste receptors and relayed to brain, where particular neurotransmitter systems process the input