We know sleep and diet are closely related, and a new study adds a few more intriguing details to the picture, showing links between specific types of foods, like those high in fibre or fat, and sleep quality.

Researchers from the University of Tsukuba in Japan dug into the data of 4,825 people who were using mobile apps for sleep tracking and diet monitoring. They cross-referenced the stats while accounting for variations in age, sex, and BMI.

"Greater total energy, fat, and sodium intakes were associated with shorter total sleep time, whereas greater protein and dietary fibre intakes were linked to longer total sleep time," write the researchers in their published paper.

In addition, people with a greater proportion of fibre in their diet also tended to fall asleep more quickly and wake up less often once they were asleep. A similar link between fibre and sleep quality has been reported in earlier studies.

While the differences here weren't huge – those who ate the most protein were averaging a little over a quarter of an hour more sleep per night, for example – the results offer some helpful pointers toward the best diets for sleep. These benefits could quickly add up over the course of weeks and months.

There are likely to be multiple factors at play here, the researchers explain. Earlier research has suggested that eating more protein boosts the production of chemical messengers including melatonin and serotonin in the brain, which help regulate sleep.

These same chemicals are also thought to be encouraged through the impact that fibre intake has on our gut bacteria. A healthier gut may be linked to healthier sleep, and vice versa.

"Recent studies suggested that changes in the gut microbiota may influence sleep and nutrient absorption," write the researchers.

It's important to note the study only used self-reported data and doesn't show direct cause and effect – there are too many unaccounted variables for that, including the timing of meals and the exercise routines of the participants.

What's more, people who are using apps for sleep and diet tracking are perhaps more likely to be interested in health in general – and the researchers are keen to compare their findings with studies that cover a wider range of participants.

The good news for those looking to improve their sleep quality is there are lots of ways to do it, backed by science – from upgrading your sleeping quarters to cutting out drinking – and now we know protein and fibre might help too.

"Dietary intake and sleep are known to have a bidirectional relationship," write the researchers. "The intake of healthy foods is associated with improved sleep quality, whereas consuming processed foods and foods high in free sugars has been shown to deteriorate sleep quality."