Imagine a child without a taste for candy. Turns out this may be remarkably common: almost one in 10 children in a recent study were unable to taste their food properly. Taste disorders such as this are known to lead to diet changes and could play a role in obesity.
David Laing at the University of New South Wales in Sydney, Australia, and colleagues tested the taste buds of 432 children aged 8 to 12. Each was asked to drink a series of water-based drinks containing either sugar, salt, citric acid or bitter quinine hydrochloride. After each drink the children were asked to point to one of three photographs that they thought best described the taste. One photograph showed a food object with the correct taste and one showed food with the incorrect taste. The third photograph always showed a glass of water in case the children found the drink tasteless.
The experiment was repeated for five different concentrations of each flavoured drink, making a total of 40 drinks. These were given to the children in a random order. Between drinks they rinsed their mouth with water.
A child is considered to have a taste disorder if they cannot point to the photograph that correctly relates to the taste in at least three of the five different concentrations of that particular flavour.
Surprisingly, 41 children – 9.5 per cent – met this criterion, with almost two-thirds of those children unable to identify a sweet taste.
Taste disorders can be caused by a variety of diseases including Bell's palsy, renal failure and diabetes. But Laing suspects that chronic middle-ear infections may be responsible for the children's disorders.
-From ear to brain
Last month, Seung Geun Yeo at the Kyung Hee University in Seoul, South Korea, found a strong association in 42 children between chronic middle-ear infections and difficulty identifying sweet and salty tastes.
A major nerve involved in tasting, called the chorda tympani, passes through the middle ear en route to the brainstem. Inflammatory proteins, viruses and bacteria from the infection can "chew up the nerve" and deteriorate taste sensations, says Laing.
In his study, Indigenous Australian children, who are particularly susceptible to ear infections, were also more likely to have taste disorders than non-Indigenous kids.
"Given the age of the children, it is likely that for many their taste loss is permanent," says Laing.
-No taste for exercise
The disorder may partly explain the rise of childhood obesity. The South Korean study found that children with taste disorders were heavier than those without. According to Laing, losing a taste sensation would "dramatically" change the taste of many foods, possibly leading to dietary switches. For example, children who could not appreciate a sweet taste may move to a high-salt diet.
The loss of taste sensations and childhood obesity is "a reasonable link", says Beverly Mühlhäusler at the University of Adelaide, South Australia. While high-fat diets and low activity levels are the main cause of obesity, taste disorders could explain why some people are more likely to make those poor lifestyle choices, she says.
But it is also possible that obese children are predisposed to getting ear infections and the ensuing taste disorders. According to Yeo, obese people have a thicker fat pad around their ear and more inflammatory proteins than normal individuals – two factors that increase the likelihood of ear infection.
*Journal references: Laing: Acta Paediatrica, DOI: 10.1111/j.1651-2227.2011.02292.x; Yeo: Archives of Otolaryngology Head and Neck Surgery, DOI: 10.1001/archoto.2011.23
**Published in "NEW SCIENTIST"