Taste buds vary widely in humans, which is one reason why some kids prefer sweet or salty treats and others do not, but it may also be the reason that some kids need more sugar to get that same sweet taste.  

In a recent Nursing Research, scholars determined the sweet taste threshold, defined as the lowest detectable level of sucrose, of 216 healthy children between the ages of 7 and 14. Each child was given two cups, one containing distilled water and the other containing a sugar solution and asked to indicate which contained a taste. This procedure was repeated across a wide range of sugar concentrations: the lowest concentration that the child could reliably distinguish from water was designated as that child's sweet detection threshold (a lower taste threshold means the child is more sensitive to that taste).

Detection thresholds varied across a large range. The most sensitive child required the equivalent of only 0.005 teaspoon of sugar dissolved in a cup of water to detect sweetness, whereas the least sensitive needed three teaspoons to get the same sensation.

To explore genetic influences on sweet taste perception, DNA from 168 of the children was analyzed to identify variation in two sweet taste genes known to be related to sweet sensitivity in adults: the TAS1R3 G-coupled protein sweet receptor gene and the GNAT3 sweet receptor signaling gene. An additional analysis identified variation in the TAS2R38 bitter receptor gene, which is known to be related to individual differences in sweet preferences among children. Small changes in each of these genes are associated with differential sensitivity of the respective receptor to its activating taste stimuli.

Genotype analyses revealed that sucrose thresholds and sensitivity were related to variation in the bitter receptor gene, but not in the two sweet receptor genes. Specifically, children whose TAS2R38 receptor gene variants make them more bitter-sensitive were also more sensitive to sucrose.

Dietary records revealed that children having this same bitter-sensitive gene variant consume a higher percentage of their daily calories as added sugar.

"Some children are twenty times better at detecting sugar than others. As sugar becomes more restricted and even regulated in children's diets, the less sugar-sensitive children may get less of a 'sweet signal' and therefore have a harder time dealing with sugar reduction," said study author Danielle Reed, PhD, a behavioral geneticist at Monell. "We were surprised to find that sweet taste sensitivity and sugar consumption were related to a bitter receptor gene. This will make us look harder at how we have cubby-holed taste genes into discrete categories and prompt us to explore whether sucrose and other sugars can directly activate bitter receptors." 

Using bioelectrical impedance to measure body composition, the researchers also asked whether sweet sensitivity might relate to measures of obesity and were surprised to find that increased body fat was associated with greater sensitivity to sweet taste.