From a study of overweight people who habitually slept less than six and a half hours: when they were made to sleep around an hour longer each night, their intake dropped by about 270 calories a day. No diet. No gym. Not a single instruction about food.

Psychologist Alfredo Rodriguez Munoz, who cites the figure, is careful with his wording: "Sleeping little does not condemn us to eating badly, but it tips the scales in that direction." And that tipped scale is exactly what no nutrition advert ever mentions, because there is nothing to sell in it.

Why the burek looks better after a bad night

It is not simply that we are hungrier the next day. "The evidence shows that when we do not rest enough, we tend to eat more, and our attraction to food rich in energy, fat or sugar increases in particular," the professor explains.

Everyone recognises this without needing a scientist. After a well-slept night, putting together a balanced breakfast is easy. After four hours of sleep, that same morning suddenly requires negotiating with yourself - and the sweet thing wins the argument before it starts.

Hormones are only half the story

Part of the explanation lies in the two hormones that regulate appetite - ghrelin and leptin. Insufficient sleep changes the signals the body uses to say "I am hungry" and "enough". But the specialist himself warns it does not stop there: "Hormones are only part of the story."

The other part is the brain. Lack of sleep hits circuits tied to reward and to behavioural control. "When we are tired, we more readily seek immediate rewards," says Rodriguez Munoz. That is why a rested person knows what they want to eat, and the very same person, after an exhausting day, decides something entirely different in five seconds.

And one much simpler calculation

There is also an explanation with no hormone in it at all. Someone who sleeps less is awake for more hours - which means more opportunities to eat, especially at night, when snacking is the easiest option in the house. Add exhaustion on top: after a long day, planning dinner and cooking takes effort that is no longer there.

When bad sleep is occasional, the consequences are occasional too. The problem starts when it becomes routine, and when the combination - greater appetite for calorie-dense food, more opportunities and weaker decision-making - repeats every day. People who sleep little run a higher risk of gaining weight, but the professor immediately adds a caveat you rarely hear: "This does not mean that sleeping little inevitably causes weight gain: our weight depends on many factors and sleep is only one of them."

The decision is made before the fridge is opened

When we want to eat better, we usually look at the plate - what to add, what to remove, how many calories there are. Rodriguez Munoz suggests looking further back, and says it with an image that sticks: "Some of the decisions we make in front of the fridge begin many hours earlier, when we decide what time we are going to bed."

The nutrition industry sells powders, plans and apps. What sleep sells is nothing - and that is exactly why we hear about it least.