If you keep skimping on sleep, scientists say you are likely to become badly overweight, because the stress on your body interrupts the balance of 'hunger hormones' ghrelin and leptin, which tell you if you are hungry or full.
As a result, people who regularly get only five hours of sleep have been found to be 50 per cent more likely to be obese than those getting eight hours.
Nutritionist Rhiannon Lambert, of rhitrition.com, says: "If you are tired and your body hasn't had enough sleep the night before to stoke energy levels, it is going to crave glucose - sugar, carbs and fizzy drinks - like crazy because it needs more energy quickly."
2. Eating too many carbs at dinnertime
If you felt famished when you woke up this morning, cast your mind back to what you had for dinner last night. If it was pizza, garlic bread and cake, you went to sleep on a major sugar high.
Refined carbohydrates such as these are made of small molecules which are quickly digested and converted into glucose - a sugar produced by the liver that fuels the brain.
Eating them causes levels of these sugars not only to rise rapidly but to drop fast, too.
The resulting low means on waking up, your brain immediately craves glucose. Hunger hormones are then released, making you want to eat as soon as possible.
To avoid starting the day hungry, experts advise dinners that combine more complex carbs - brown rice, whole grain breads and pastas, which are processed more slowly by the body - with proteins, such as meat, fish or nuts, which are also more difficult to digest.
Endocrinologist Sir Stephen O'Rahilly, a professor at Cambridge University, says carbs don't switch off hunger hormones as well as other foods.
"Inside your intestines are tiny sensor cells which detect how much protein and carbs you have eaten.
"Protein stimulates these cells more strongly than carbs, which is why it's harder to eat too much steak than too much pizza. You need to include protein in meals to tell your brain you have had enough."
3. A big night out with friends
Drinking doesn't just land you with a raging hangover the next morning. It can also give you the munchies.
Research published in the journal Alcohol And Alcoholism found just three glasses of wine can lower levels of hormone leptin, which keeps hunger at bay, by up to 30 per cent.
Also, your liver will have spent so much time breaking down the alcohol in your blood overnight it won't have been able to deliver the levels of glucose your brain needs to function.
Professor O'Rahilly, says: "If you poison your liver with alcohol, it does not make the normal amount that your brain is used to. So when you wake up, it screams emergency because it wants glucose so badly."
4. Mouthwatering food ads
With food adverts tempting us everywhere we go, no wonder eating is always on our minds.
Just looking at pictures of appetising meals can make you hungry, according to researchers at Germany's Max Planck Institute of Psychiatry.
They found we produce more nof the hunger hormone ghrelin when we see the images.
Tempting food smells set off cravings, too. New York-based Brookhaven National
Laboratory found our brains light up when we smell our favourite foods - in the same way that those of cocaine addicts do when they think about their next drug fix.
The result of all this is that we no longer just eat when we are hungry, says Alison Clark, of the British Dietetic Association.
"Triggers like food ads can actually make people want to eat - even when they don't need to."
5. Not drinking enough water
You think you're peckish - but if you don't take on enough fluids, you may be misinterpreting your thirst as hunger. When we are dehydrated, these messages become confused in the hypothalamus, the part of the brain which regulates appetite hormones, so we reach for a snack when we actually need a drink.
Nutritionist Rhiannon Lambert says: 'Our body is 60 per cent water and all our cells need it. If you're dehydrated, you're going to start getting moody, tired, losing concentration. However, that feeling can get confused in the brain with hunger as it has the same effects.
"People should therefore aim for about two litres a day minimum, even when you don't actually feel thirsty, to avoid this confusion."
6. Suffering the 'buffet effect'
The trend for importing cuisines from all over the world means we have never enjoyed a wider range of exotic flavours.
But eating lots of different types of food at one meal - known as the 'buffet effect' - can trick us into eating more than we need.
A study in the Journal Of Consumer Research found diners tend to eat 10 per cent more if offered a variety of foods.
When faced with a large choice at one meal, researchers think our eyes con us into underestimating the quantities of each dish. Over a year, this 'optical illusion' can lead to weight gain of up to 20 lb.
Therapist Marisa Peer, author of You Can Be Younger, says studies show how a new taste can also reset our appetite - even when full.
"There is only so much of one food we can have before we get bored and stop eating. When you are given a taste, even if feeling full, it stimulates your appetite again.
"This is why you still have room for dessert after a filling Sunday lunch."
7. Wolfing down your meal
When you rush a meal, you may fill your stomach quickly. But your brain needs time to register you've had enough.
Experts say it starts to realise you are full only when your meal begins to be digested.
"It takes about 20 minutes for your body to register and for your receptors in your stomach to reach the brain and say: 'Thanks very much. I'm full. Stop eating,'" says Alison Clark of the British Dietetic Association.
"So we suggest taking time to pause after a meal instead of going on to the next course in order to allow the chemical signals to reach the brain."
8. Your period is on the way
If your period is on the way, the biscuit tin will be much harder to resist.
During the second half of your menstrual cycle, levels of the sex hormone progesterone rise as your body gets ready for pregnancy by sending blood to the womb.
As part of this preparation, it also triggers hunger hormones to persuade you to eat more and give your body the reserves to grow a baby.
In one study published in the Journal Of Affective Disorders, 74.3 per cent of women said they suffered food cravings before their period, compared to 56.3 per cent during menstruation and just 26.9 per cent afterwards.
As your period approaches, levels of the female sex hormone oestrogen also dramatically drop off - and with it levels of the feelgood hormone serotonin.
Lucia Lukanova, founder of The Flow app, which helps women chart their cycles, says: "Women's food cravings start in the last week before their period when their progesterone and oestrogen levels fall.
"This sudden withdrawal is like taking cigarettes away from a smoker so we crave alternatives, like comfort foods, to make us feel better."
