Distaste for sprouts in the genes
Raw veg study sheds light on bitter taste sensations.
In the name of science (and for a small fee), 35 brave individuals volunteered to take part in an extensive taste test of raw broccoli, cauliflower, Brussels sprouts and 25 other bitter vegetables. The results help to explain why some people have a natural aversion to these veggies.
Researchers previously knew that the tongue carries a receptor called TAS2R, which comes in several different forms. Only those people carrying a 'sensitive' form of this receptor have been found to be able to taste bitter chemicals such as phenylthiocarbamide (PTC), and researchers had suspected that these same people may be turned off vegetables that contain chemically similar compounds called glucosinolates.
But this conclusion was uncertain: in vegetables, the taste of these compounds may be masked by other chemicals.
Mari Sandell and Paul Breslin of Monell Chemical Senses Center in Philadelphia, Pennsylvania, wanted to test the theory. They gave the willing victims 17 raw vegetables known to be rich in glucosinolates a shopping list that includes some vegetables that have nauseated generations of school kids, such as broccoli, cauliflower, Brussels sprouts, radish and turnips.
The volunteers also swallowed 11 vegetables that are bitter but lack glucosinolates, including aubergine, bitter melon and spinach.
The veggies were served raw because cooking can alter their taste. Each person chewed the vegetable ten times to the tick of a metronome; then they spat and cleaned their mouth with water and crackers.
Genes for greens
Swabs were also taken of the volunteers' cheek cells so that researchers could determine whether they carried none, one, or two 'sensitive' copies of the taste receptor gene that allows taste of PTC.
People carrying two 'sensitive' copies of the gene rated the glucosinolate-carrying vegetables as around 60% more bitter than the group carrying two 'insensitive' copies of the gene. The two groups ranked the vegetables lacking glucosinolates as equally bitter. The results are reported in Current Biology1.
The findings support the idea that a person's genes (and particularly this gene) help to explain whether they nudge some vegetables to the side of their plate, or gobble them up.
Our ability to taste bitter compounds is of particular interest to some researchers because such chemicals are often medicinally active for better or for worse. Researchers have wondered whether being able to taste certain chemicals puts us at an evolutionary advantage.
Glucosinolates can interfere with uptake of iodine by the thyroid, for example. Iodine, found in some salts and seafood, is essential for the synthesis of thyroid hormones, which in turn can affect mental and reproductive growth or development. According to one long-standing hypothesis, in geographic regions where iodine is naturally low, those carrying the 'sensitive' form of the taste receptor may be at an advantage; avoiding foods containing glucosinolates would allow their thyroids to be healthier.
On the other hand, vegetables such as broccoli also carry an assortment of other nutrients thought to be good for health. So in areas where iodine is plentiful, those carrying the 'insensitive' form of the taste receptor gene might eat more of them and benefit. These two opposing selective pressures could be keeping the two forms of the gene in circulation.
Breslin points out that taste alone does not determine whether we eat bitter foods; culture also plays a part in our liking of coffee, beer or liquorice. So taste genes will only make up part of the reason for an individual's vegetable loves or hates.
It is also possible that the types or quantities of receptors on our tongues change over time, perhaps explaining why children turn up their noses more than adults at bitter foods.
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- Sandell M. A. & Breslin P. A. S. Curr. Biol. , 16. R792 - R794 (2006).