And they have nothing to do with an empty stomach. Consultant cardiologist, health campaigner and co-author of the Pioppi Diet Dr Aseem Malhotra explains how to outsmart the appetite gremlins

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Ever wondered why you're hungry even though you've just eaten or how you reached for a snack without even realising? Modern lifestyles and food choices are messing up our natural appetite responses. Here are the five most common ways this happens and steps you can take to get your appetite back to its natural state.

1. Eating too many high glycaemic index foods

Why? Constant blood sugar spikes and dips make you crave more.

The higher our blood glucose, the more insulin the body produces to regulate levels. Doing this occasionally is not a problem but if you’re constantly consuming high glycaemic index (GI) foods, this encourages you to feel constantly hungry. High GI foods that can raise blood glucose aren't necessarily 'sweet' foods. A 150g serving of white basmati rice, for example, produces a blood glucose response equivalent to 10 teaspoons of sugar. A 150g baked potato and white bread both have the equivalent of eight teaspoons and while spaghetti has six-and-a-half.

A high GI diet encourages you to feel constantly hungry, because chronically raised insulin stops the hormone leptin - released by our fat cells - from telling the brain we’re full. This creates a vicious cycle of snacking on processed sugary foods. This, in turn, leads to insulin resistance and weight gain.

Insulin's primary function is to maintain blood glucose levels within a normal range for our cells to do their job properly, but it is also responsible for converting excess energy into fat for storage, so it’s also known as the fat storing hormone.

Insulin resistance happens when the body becomes resistant to insulin over time, when it’s produced by the pancreas in excess. Insulin resistance is not only a number one risk factor for heart attack, a precursor for type 2 diabetes and high blood pressure, and is also independently associated with dementia and many cancers even in people with a normal body mass index.

What you can do:

* On the Pioppi Diet , we recommend going cold turkey on all added sugars, fruit juice, honey and syrups and refined carbs for at least 21 days.

MORE GLOSS: The Pioppi Diet Weekly Meal Plan

* After that, see refined carbs to be eaten not at all or as an occasional treat. The people of Pioppi (the village in southern Italy, known as the home of the Mediterranean diet and where people live on average ten years longer than anywhere else) ate pasta only as a starter, not as a main course, with extra virgin olive oil which reduces the glycaemic index (blood sugar response) of the food. This was against a background of very low sugar consumption with dessert eaten once a week, usually on Sundays. Interestingly, the type of bread eaten in Pioppi was baked in the home taking more than 24 hours. Modern supermarket bread is heavily processed and has a much higher glycaemic index.

* Choose foods which are both satiating nutritious and have the least impact on blood glucose levels - fibrous vegetables, healthy high-fat foods such as cheese, full-fat yoghurt, extra virgin olive oil, nuts and protein.

2. Eating refined sugar

Why? It messes with your hunger hormones.

Normally when we eat, our stomach produces less of the hunger hormone ghrelin. Not so when we eat sugar; fructose (which makes up 50 per cent of refined sugar, the other 50 per cent is glucose) doesn’t suppress grehlin, thereby keeping us hungry.

Secondly, chronic excess consumption of refined sugar raises insulin levels, as above. Over time, the result is that the brain stops responding to the fullness hormone leptin, so on that front, the brain doesn’t know we are full either.

What you can do:

* Beware healthy-sounding sugar alternatives: agave nectar is in fact 55 to 97 per cent fructose, depending on the brand. The latest advice from the World Health Organisation suggests a maximum of six teaspoons of Non Milk Extrinsic Sugar (NMES) a day -  that includes added sugar, fruit juice, honey and syrups.

* Avoid artificial sweeteners: there’s growing evidence that they act on areas of the brain that stimulate appetite.

* Avoid processed foods – it goes without saying they are often high in hidden sugars.

* My advice is if you’re craving something sweet swap the chocolate bar for a piece of whole fruit such as apple. The small concentration of fructose is counteracted by the fibre content which slows the absorption into the blood stream, and helps you feel full in addition to containing vitamins and antioxidants.

3. Too much stress

Why? Stress hormones increase appetite.

Chronic stress appears to increase the hormone cortisol which stimulates appetite. Research also suggests that under stress (both acute and chronic) we’re likely to choose high glycaemic index comfort foods thus driving a vicious cycle.

What you can do:

* Breathe to reduce stress: Meditation reduces stress and the Pioppi Diet recommends a simple breathing technique which takes just two minutes four times a day. For those two minutes, breathe in for five seconds and breathe out for five. Finding a total of eight minutes a day to do this is not difficult.

* Regular exercise e.g. brisk walking for 30 minutes a day, five times a week has been shown to reduce insulin resistance within weeks. Mindful movement in the form of Pilates or yoga is a great mitigator of stress.

* Do what you love, whether it be dancing, cycling or even having sex. As well as the physical benefits regular physical activity also boosts the feel good or happiness hormone serotonin. There’s also evidence for women, regular orgasms release the hormone oxytocin that counteracts the effects cortisol, the stress hormone that makes us hungry. Even hugging releases oxytocin. Spend more actual time with friends and family and less time on social media.

4. Poor sleep

Why? poor sleep makes you less insulin sensitive and messes with your food choices

There’s extensive research that points to poor sleep being a risk factor for many diseases and conditions which include high blood pressure, type 2 diabetes, heart disease, obesity and depression. We’ve all experienced how good and energised we feel after a good night’s sleep and how just one bad night can put us at the opposite end of the spectrum.

Just one night of poor sleep also makes you less insulin sensitive. Testosterone has been shown to slide, cognitive performance diminishes which make us feel less in control of making healthy food choices. After one night of restricted or broken sleep, we may perform poorly all round and have a greater propensity to make poor ‘pick-me-up’ food choices throughout the day.

What you can do:

* The major cause of poor sleep is stress (see above!). Try to switch off from social media and computer screens at least two hours before bed. Avoid caffeine after lunchtime. Overall lifestyle changes that incorporate a good diet, regular exercise and meditation, which we advocate on the Pioppi Diet, will also enhance longer and more productive sleep.

* Make time or sleep: evidence points to seven hours as a minimum recommendation to reap the powerful benefits of a good night’s sleep.

5. An 'unhealthy' food environment

Why? Our drive for instant gratification makes us likely to make unhealthy choices.

Our 'food environment' has the biggest impact on our behaviour when it comes to what we eat. Our food choices are often made without full conscious awareness and so may be difficult to control.  Professor Theresa Marteau, Director of the Behaviour and Health research unit at the University of Cambridge explains: “We are heavily influenced by automatic behaviours which require little cognition, where the desire for instant gratification far outweighs greater, more distant rewards, which makes us more likely to act in unhealthy ways.”

So despite wanting to lose weight or choose the fruit instead of the Haribos,  we’re still tempted by the brightly-coloured packaging at the checkout till or in our cupboard.

What you can do:

* Remove all sugary snacks, biscuits, crisps and sweets from your house to take away those easy temptations.

* If you do have to snack on something while following the Pioppi Diet, choose something healthy and satiating like a handful of nuts or a piece of cheese.

The Pioppi Diet, a 21 Day Lifestyle Plan by Dr Aseem Malhotra and Donal O'Neill is published by Penguin Michael Joseph £8.99.  Buy it here . Follow Dr Malhotra on Twitter  @DrAseemMalhotra