Dr Michael Mosley suggests the best foods to destress

We all feel bad about putting on weight, mainly because we assume it is entirely our own fault. After all, the only way to pile on those extra pounds is to eat more in calories than we burn off in exercise.

But why do we do we overeat? Why do we reach for a slice of cake, a packet of biscuits or a bar of chocolate? Sometimes it is just more difficult to resist temptation – I find it incredibly hard to say no to chocolate, for example.

But I don’t believe we become fatter simply because we are greedy and slothful.

Instead there is compelling scientific evidence that there is one aspect of our psychological wellbeing that plays a huge part: stress. Research has shown that chronic stress leads to increased hunger, comfort eating, self-loathing and disrupted sleep. This, in turn, leads to even higher levels of stress.

To lose weight and keep it off it is important to reduce stress – and all the comfort eating that goes with it. This will not just make you feel better, but make you look better too.

So what is stress, what is the link to overeating, and what can you do about it? Today, in the first of an exclusive two-part health plan in The Mail on Sunday’s new Life section, I outline some simple steps you can take to de-stress – and help you stick to your New Year’s weight-loss resolutions.

But let’s begin by debunking some myths…

Simple breathing exercises and yoga have been shown to be beneficial to lowering stress

STRESS IS NOT ‘ALL IN THE MIND’

Having some level of stress in your life is essential for survival. Imagine that you are crossing the road and you are almost run down by a car. As you instinctively leap away from the danger, your body releases huge amounts of stress hormones such as cortisol and adrenaline, which ready the body for physical action.

This is the ‘fight or flight’ response, and it evolved because in the distant past it would have helped us avoid being eaten by large, hungry predators.

This is a good thing. The real problems occur when levels of these stress hormones go up and stay up.

To demonstrate just what can happen, in Wednesday’s episode of the long-running BBC2 series, Trust Me I’m A Doctor, my colleague Dr Giles Yeo, a scientist from Cambridge University, takes part in a series of stress-inducing experiments.

It starts with researchers putting Giles through something called the Maastricht Stress Test, which is designed to activate the human stress response.

First of all, Giles was made to do some quick mental maths – and he kept making mistakes, which for an academic is particularly stressful.

Then they got him to put his hand in a bath of ice-cold water and hold it there, as the discomfort is known to trigger the stress reaction.

Throughout these tests Giles’s blood sugar levels were measured. Giles normally has healthy, low, blood sugar levels, but when he was stressed his levels soared and then took three hours to return to normal – six times longer than they had done on a previous, stress-free day.

This happens because when your stress hormones go up, your body pumps lots of extra sugar into your blood in order to provide energy for your muscles in preparation for ‘fight or flight’. But if you do not use up that sugar with physical activity, then your body produces another hormone, insulin, to bring those blood sugar levels back down again.

The sugar which has been removed from your blood is stored as fat in your liver and around your stomach.

Rising levels of insulin and falling blood sugars will also make you really hungry. This is why you will crave yet more sugary carbs when you are stressed out.

MOOD-CHANGER: A Mediterranean-style diet can help to reduce stress

HOW INSOMNIA FEEDS YOUR HUNGER

The same sort of thing happens when you have a bad night’s sleep, as I discovered when I recently joined Dr Eleanor Scott, of Leeds University, in a short, sharp sleep deprivation experiment.

For this experiment, Dr Scott recruited a group of healthy volunteers and fitted them with glucose monitors, so that she could see what was happening to their blood sugar levels. Then she asked the volunteers to have two nights where they went to bed three hours later than normal, followed by two nights where they could sleep as long as they liked.

Naturally enough, being an avid self-experimenter, I joined in. It was pretty grim. I was also unpleasantly surprised by just how much my blood sugar levels rose on the days when I was sleep-deprived, and how hungry I was.

The same was true for all my fellow volunteers – everyone complained about having had the munchies. As one of them told me: ‘I wanted lots of biscuits and I didn’t just have one – I had ten custard creams.’

‘Is that unusual?’ I asked him.

‘Well it is certainly unusual for breakfast!’ he replied.

All of us, whether we had feasted on biscuits or managed to stick to our normal diet, saw big increases in our blood sugar levels, to the point where previously healthy individuals had levels you would see in type 2 diabetics. Fortunately, these problems were resolved after a couple of nights of good sleep.

Sleep and stress are closely linked: being stressed leads to problems sleeping, and problems sleeping make your stress levels soar.

So it is not surprising that being sleep-deprived leads to many of the same hormonal changes and cravings as being stressed.

A recent study by researchers at King’s College, London, found that if you sleep-deprive people they will consume, on average, an extra 385 calories per day, which is the equivalent of a large muffin.