Monell scientists research how age modifies taste receptors

"What is food to one man is bitter poison to others." - Lucretius, Roman poet and philosopher

If your child rejects certain healthy but bitter-tasting vegetables, this may not be just obstinacy. The choice is likely influenced by their DNA. The ability to detect bitter-tasting chemicals is an adaptation that enables an organism to recognize and avoid ingestion of potentially toxic foods. The gene responsible for this trait is TAS2R38 (taste receptor, type 2, member 38).

In a recent study conducted at the Monell Chemical Senses Center in Philadelphia, authors Julie A. Mennella, M. Yanina Pepino, Fujiko F. Duke and Danielle R. Reed measured the relationship of the ability of humans of various age groups to taste the bitter compound 6-n-propylthiouracil (PROP) to an individual's TAS2R38 variants.

Some individuals can taste the bitter compound PROP at very low concentrations, some only at higher concentrations, and some not at all. This ability is linked to ones genes. Although a simplification, having the gene variant AVI is an allele for non-tasting, and the variant PAV allows an individual to detect the bitter-tasting PROP.

We have a pair of genes for every trait (one from Mom and one from Dad). 37% of the 980 individuals tested were heterozygous ---having one copy of AVI and one copy of PAV (AVI/PAV). 18% were homozygous (having two identical copies) for non-tasting (AVI/AVI) and 17% were homozygous for tasting (PAV/PAV). The remaining persons had one or more of other rare variants for TAS2R38 in their genotype (genetic makeup).

The researchers used a clever and very charming method to record taste perceptions that would be both understandable and fun for subjects as young as three years old. If a sample liquid tasted like water, the subject was told to give it to a stuffed toy of Big Bird from Sesame Street. If the liquid was bitter or "yucky", the subject was told to give it to Oscar the Grouch so that he can "throw it in his trash can."

The scientists found that subjects with the same gene combinations had similar abilities to taste the bitter compound PROP, results that transcended race/ethnicity and sex.

More importantly, individuals who were heterozygous (having both AVI and PAV variants) varied in their ability to taste PROP by age. AVI/PAV children could perceive a bitter taste at lower PROP concentrations than AVI/PAV adults, with the taste thresholds of adolescents being intermediate. Similar age effects were not observed with homozygous (AVI/AVI or PAV/PAV) groups.

It is postulated that enhanced ability to taste bitter compounds at a younger age could be advantageous in the avoidance of  thyroid poisons found naturally in plants that could impair growth and development.

In addition, acceptance or rejection by children of healthy, but somewhat bitter-tasting vegetables, may be a "reflection of their basic biology."

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