'Negative calorie foods are foods, which use more calories to digest than the calories the foods actually contain,' states website negativecaloriefoods.com.
'Calories from these foods are much harder for the body to breakdown and process. In other words, the body has to work harder in order to extract calories from these foods. This gives these foods a tremendous natural fat-burning advantage.'
A piece of dessert consisting of 400 calories may require only 150 calories to be digested by our body, resulting in a net gain of 250 calories which is added to our body fat.
According to this theory, for example, if you eat 100 calories of a food that requires 150 calories to digest, then you've burnt an additional 50 calories simply by eating that food,' it continued.
If you are looking to lose weight or simply to lead a healthier lifestyle, adding these to your diet (or even better - swapping the crisps and chocolate for them) could be the perfect way to help you, we list below 10 guilt free foods which use more calories to burn then they contain themselves:
Calorie content:100g contains 16 calories
Made mostly of water, a cucumber is also a great source of vitamin C and is known to be able to reduce high levels of inflammation in the body.
'Cucumber contains ascorbic acid and caffeic acid help prevent water retention,' Daisy Connor, nutritionist at NutriCentre, said.
Calorie content: 100g contains 20 calories
A good way to detox (it contains diuretic nutrients that can help remove toxins), eating asparagus can also help boost your metabolic rate.
As well as its pound-shedding properties, asparagus is also rich in folate which makes it an ideal food for pregnant women as folate can reduce the risk of life-threatening conditions.
Calorie content: 100g contains 25 calories
It's a current food trend with everything from rice, mash potato and pizza bases being made out of it.
But cauliflower has long been a friend of the dieter as it contains no fat, is high in Vitamin C and has such a strong flavour that it can stand alone on its own.
Eat it raw or lightly steamed so that it remains crunchy, which will take you longer to chew which will give your body the time to realise you're full.
'Cauliflower is also excellent source of fibre and vitamin K,' Ms Connor said.
Calorie content: 100g contains 16 calories
An obvious choice for most dieters, approximately 75 per cent of a celery stick is actually water. The other 25 per cent is fiber. The high water content of celery means that you will burn more calories eating it than it actually contains.
Ms Connor advised: Rich in sodium and potassium, add celery it to a post-workout juice for electrolyte replacement.'
Calorie content of lean pork: 100g contains 145 calories; calorie content of turkey leg: 100g contains 144 calories; calorie content of chicken breast: 100g contains 172 calories
Not strictly a negative calorie food, lean meats such as pork, turkey and chicken are excellent sources of protein, which make the digestive system work harder, temporarily boosting your resting metabolic rate which in turn helps you burn more calories.
Your body takes more energy to digest meat proteins than it does to digest carbohydrates, which is why high-protein diets such as the Atkins are popular.
Additionally lean meats are a great source of energy, which means they will keep you fuller for longer, ensuring that you don't eat as much as you would normally.
So, while they may contain more calories than celery or cucumbers, they are still a good way to help you burn calories.
'Fat contains more calories per gram than protein does per gram, so trimming all visible fat from meat or choosing lean meat such as chicken makes your meal lower in calories.
'At the same time, having more protein in your meal will keep you fuller for longer compared to a mainly carbohydrate meal,' Ms Connor explained.
Calorie content: 100g contains 18 calories
Bursting with flavour and full of lycopene, tomatoes aare some of the best foods to include in your diet. As well as being low in calorie content, their health benefits increase when they are cooked.
Scientists said that cooked tomatoes can have the same benefits as statins for patients battling against high cholesterol levels or high blood pressure.
They could be an ‘effective alternative’ to statins, the class of drugs commonly prescribed for these conditions which can lead to heart problems, according to a study.
And just two ounces of tomato paste or a pint of juice a day could be enough to help many patients.
The secret lies in high levels of the compound lycopene which gives ripe tomatoes their bright red colour.
This powerful anti-oxidant is essential for good health as it helps lower the risk of heart attacks and strokes.
Ms Connor said: 'Tomatoes are rich in vitamin C and lycopene which has lots of antioxidant action.'
Calorie content of papaya: 100g contains 43 calories
Fresh papaya contains less calories per gram, so eating it allows you to fill up without actually affecting your quota for the day.
They are just as rich as oranges in vitamin C and contain 15 times more of the antioxidant beta-cryptoxanthin, thought to reduce the risk of polyarthritis (where the condition affects several joints at once).
Papaya's fibre is also good for combating constipation and keeping cholesterol in check.
'Lots of fibre and antioxidants including vitamins C, E and A in papaya, said Ms Connor. There is also the digestive enzyme papain.'
Calorie content of chili peppers: 100g contains 40 calories
That mouth-burning sensation you get when you bite into a chilli? That's what makes this hot little pepper one of the best calorie-burning foods.
Containing capsaicin, chillies have the ability to boost the metabolic rate, which in turn causes the body to burn more calories immediately after you eat them.
The amount of calories contained in chillies is so negligible that when you eat them, they end up burning more calories than you actually consume.
Try adding hot sauce or chilli flakes to your dishes as chillies have another superpower — eating more of them can help curb your appetite.
Calorie content of apples: 100g contains 52 calories
But only green ones. Skip Red Delicious and go instead for Granny Smiths and you'll be well on your way to shedding those pounds.
While not strictly a negative calorie food, green apples are rich in dietary fiber, helping you feel fuller for longer periods of time.
A study published in 2013 in 'ISRN Obesity' reported that dietary fiber enhances satiety, reduces hunger and is beneficial for weight loss — so for those looking to lose weight, apples are pretty much the perfect food.
'Apples contain lots of fibre which makes it lower on the glycaemic index than many other fruits,' Ms Connor explained.
Calorie content of plain brewed black coffee: Two calories
Yes, that cup that gets you through the morning (and for some of us, throughout the day) contains zero calories — when drunk on its own.
Have it black and it'll be one of the best weight-loss adds you could have.
But adding sugars, syrup or milk will make the calorie content a cup of java soar, so if you're trying to slim down, steer clear of any extras.
Coffee should be drunk in moderation as too much of caffeine in your system can cause a strain to your heart
'Coffee is thermogenic and stimulates the burning of fat for energy,' Ms Connor said
The drink can also reduce your cravings as it can change the level of hormones in your digestive system that alert you whether you are hungry or full. Added bonus? Caffeine also boosts your metabolic rate.