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If you are frequently tempted to buy a treat from the pastry case at your favourite coffee shop, there’s a good reason - and it’s not just your lack of willpower.

A new study on coffee has found that caffeine can affect the way we perceive sweetness and may make us crave sweets more strongly.

Caffeine gives us an energy jolt because it blocks receptors in our brain for adenosine, a chemical that can make us feel sleepy. Previous research established that adenosine also helps us taste sweet flavours.

For this study, scientists at Cornell University gave participants a cup of lightly sweetened coffee, and didn’t tell them if it contained caffeine (the purely decaf cups contained quinine, so both types of coffee had the same level of bitterness). The participants were “unable to estimate the caffeine content of their sample,” the study said.

But the ones who drank caffeine perceived their coffee to be less sweet than those who unknowingly drank decaf. Asked to taste and rate a sucrose solution five minutes later, they still reported tasting lower levels of sweetness.

The dulled palate for sweets “is a noticeable effect”, and sticks around, the scientists said.