A sleep disorder that can leave people gasping for breath at night could be linked to the amount of fat on their tongues, a study suggests.
When sleep apnoea patients lost weight, it was the reduction in tongue fat that lay behind the resulting improvements, researchers said.
Larger and fattier tongues are more common among obese patients.
But the Pennsylvania team said other people with fatty tongues may also be at risk of the sleep disorder.
The researchers now plan to work out which low-fat diets are particularly good at slimming down the tongue.
"You talk, eat and breathe with your tongue - so why is fat deposited there?" said study author Dr Richard Schwab, of Perelman School of Medicine, Philadelphia.
"It's not clear why - it could be genetic or environmental - but the less fat there is, the less likely the tongue is to collapse during sleep."
Sleep apnoea is a common disorder that can cause loud snoring, noisy breathing and jerky movements when asleep.
It can also cause sleepiness during the day, which can affect quality of life.
The most common type is obstructive sleep apnoea, in which the upper airway gets partly or completely blocked during sleep.
Those who are overweight or who have a large neck or tonsils are more likely to have the condition.
How to help sleep apnoea
Try to lose weight if you are overweight
Sleep on your side - try a special pillow to help
Give up smoking
Do not drink too much alcohol, especially before bed
Don't take sleeping pills unless recommended
Researchers at the Perelman School of Medicine, University of Pennsylvania, scanned 67 people with obstructive sleep apnoea who were obese and had lost 10% of their body weight, improving their symptoms improved by 30%.
By looking at the size of patients' upper airway structures, the research team was able to find out what changes had driven the improvements.
The patients' weight loss also led to a reduction in the size of a jaw muscle that controls chewing and muscles on either side of the airway, which also helped.
"Now that we know tongue fat is a risk factor and that sleep apnoea improves when tongue fat is reduced, we have established a unique therapeutic target that we've never had before," said Dr Schwab.
The study is published in the American Journal of Respiratory and Critical Care Medicine.