Could your carbohydrate cravings be down to a 'sixth taste'?

Even the most committed dieters find it hard to say "no" to a bag of chips - but there could be more to our devotion to carbohydrate-rich foods than simple greed.

New evidence suggests that humans can taste the starch in foods, such as bread, and it may even constitute a "primary taste" in its own right.

"Every culture has a major source of complex carbohydrate. The idea that we can't taste what we're eating doesn't make sense," says Juyun Lim, a researcher at Oregon State University.

Lim has been testing the ability of volunteers to detect a starch-like taste in solutions containing various types of carbohydrate molecules. Complex carbohydrates such as starch are made up of arrangements of sugar molecules and it was previously thought that humans tasted these sugar molecules as they were broken down by enzymes in our saliva, says Lim.

However, her study showed that people were able to pick up the flavour of complex carbohydrates.

"They called the taste 'starchy'," she told the New Scientist. "Asians would say it was rice-like, while Caucasians described it as bread-like or pasta-like. It's like eating flour."

The volunteers were able to make out the floury taste even when they had been given a compound that blocks the receptors on the tongue which detect sugar molecules, suggesting that we can taste carbohydrates before they are broken down.

Previously it was thought that our tongues register a small number of tastes – salty, sweet, sour, bitter and umami – a savoury taste.

In 2015, scientists at the Ingestive Behaviour Research Centre at Purdue University in Indiana published research that suggested humans could also taste fat.

But before any new flavours can be categorised as primary tastes, they must tick a number of boxes. Tastes need to be recognisable, have their own set of tongue receptors, and trigger some kind of useful physiological response.

Starch doesn't satisfy these criteria yet: Lim and her colleagues have not been able to identify specific starch receptors on the tongue but she is convinced it is useful to us.

"I believe it's why people prefer complex carbs," says Lim. "Sugar tastes great in the short term, but if you're offered chocolate and bread, you might eat a small amount of the chocolate, but you'd choose the bread in larger amounts, or as a daily staple."