Hoping to lose a few pounds before Christmas but gloomy about your chances of success with conventional diets? Then lemons could be the answer.

In a new book, The Lemon Juice Diet, leading health writer Theresa Cheung suggests that the reason so many of us battle with our weight is because our digestive systems are not working properly - and that the conventional dieting process tends to exacerbate that.

However, including lemons in your diet - both juice and peel - will boost your digestion and, if you also eat healthily and exercise, can help you lose weight.

"Research seems to show that if your digestive system is not working correctly, healthy weight-loss is almost impossible," says Cheung. "The problem is that poor digestion can stop your body getting the nutrients it needs to burn fat. It can also cause a build-up of toxins in your body, leaving you feeling sluggish and depressed.

"This, in turn, slows down your metabolism, making any weight-loss goals unattainable."

Furthermore, she says, if your body isn't absorbing the right nutrients, then no matter how overweight you are, it thinks it is malnourished and constantly craves nutrients, telling you you're hungry when you're not.

The solution is lemons. "When it comes to boosting the body's digestive and detox systems, lemon is a natural powerhouse," says Cheung.

Lemons are rich in citric acid (at seven to eight per cent, they have the highest concentration of all fruits), which, she explains, "combines in a complex interaction with other acids and enzymes to ensure healthy and problem-free digestion by stimulating stomach juices".

"Thanks to its acidity, even a little lemon juice can improve your digestion and lower the impact of any meal on your blood sugar," she adds.

The pectin in lemon - found in the peel - is a great source of fibre that helps weight loss by turning into a sticky gel when you digest it, preventing your stomach from absorbing sugar too quickly.

A study published in the Journal of the American College of Nutrition found pectin can eliminate the urge to eat for up to four hours, because after eating it you tend to feel satisfied for longer.

Lemon juice is also one of the most concentrated food sources of vitamin C. Not only is this great for warding off colds, but recent research at Arizona State University suggests that people who eat fruit and vegetables high in vitamin C have more efficient digestive systems and are more likely to lose weight than those who don't.

In addition, lemon juice increases the acidity of the digestive system. This helps the body absorb calcium, which is then stored in fat cells. Research has shown that the more calcium there is in a fat cell, the more fat the cells burn.

It seems the humble lemon could be a powerful aid to digestion, and a useful diet booster.

But it's not a case of eating only lemons: the good news is that you can eat perfectly normal foods on this diet, including cheese and other proteins. You can even have chocolate ice-cream.

You can also eat as much as you like of the right sort of foods: there is no calorie-counting involved. All you have to do is make sure that at least one meal a day includes lemon - either a squirt of juice or some peel.

The Lemon Juice Diet advocates a simple healthy-eating plan based on seven principles. These are the principles on which the meal plan is based, but you can use them to adapt the meals to suit your tastes.

If you combine these seven principles with an exercise regime involving 30 minutes of aerobic activity five or six days a week, within just a week you should start feeling healthier and your clothes will be looser. By week two, you will be dropping pounds.

THE SEVEN PRINCIPLES

The following rules will help you achieve the weight loss and fat burning you want.

1. Drink lemon juice with warm water every morning. Starting the day with the juice of a lemon in a glass of warm water will stimulate your digestive system.

Water is also crucial to weight loss. Water aids healthy digestion and the elimination of waste, so make sure you drink six to eight glasses a day. Alcohol should be limited to one small glass of wine a day, and keep coffee and tea to a minimum. Avoid fizzy drinks and sweetened fruit juices.

2. Eat at least five portions of fruit and vegetables a day. All vegetables and most fruits are low-calorie nutritional powerhouses, rich in vitamins, minerals, fibre and nutrients that can boost immunity, balance hormones, calm the nervous system, aid digestion and help weight loss.

3. Balance your blood sugar levels. Irritability, poor concentration, fatigue and headaches are all symptoms of fluctuating blood sugar levels, which can make you crave sweet and fattening foods. When blood sugar levels swing too high, so does insulin. This hormone helps shuttle blood sugar (glucose) into your cells to be used as energy. In other words, it promotes fat storage.

Sprinkling lemon juice over your meal can be enough to lower the blood sugar impact by as much as 30 per cent - use it in all your cooking. Using peel in cooking helps ensure the sugar is released steadily into your bloodstream. Add peel to soups and salads, and sprinkle on fish and chicken. Lemons are also a fantastic source of fibre.

Eat protein with each meal, as it steadies your blood sugar by delaying the absorption of carbohydrates and fats. Eating five or six times a day will combat food cravings.

4. Cut down on sugar-rich foods. This give you a brief high followed by a big slump, and leave you feeling edgy and tired. Refined foods - such as white bread , white rice, instant potatoes and cornflakes - can act like sugar in your system, and end up being stored as fat. Instead, stick to whole grain, fruit, vegetables and protein.

Natural sugars in fruit can hit your bloodstream fast, so don't eat a piece of fruit without a handful of nuts or seeds to slow the impact. Beware of artificial sweeteners as they can increase sugar cravings.

5. Forgot low fat - your body needs some fat to lose weight. Unsaturated fats can help with weight loss by delaying the passage of carbohydrates into your bloodstream, keeping blood sugar levels stable and insulin down.

Avoid saturated fats - found in red meat, cakes and pastries - and trans-fatty acids in processed foods. These are low in nutrients and can increase your risk of heart disease and obesity.

Increase your consumption of omega 3 and omega 6 essential fatty acids found in nuts, seeds and oily fish, and unsaturated fat found in extra virgin olive oil.

6. Eat lots of fresh whole foods. Switch from processed to whole foods to boost your intake of the nutrients your body needs for weight loss. Whole foods such as beans, pulses and lentils also contain fibre, which stimulates the digestive system and can slow down the conversion of carbohydrates into glucose.

Best of all, whole foods are free of hidden sugar and chemicals that overload your liver, making it hard for your body to digest food and burn fat. Choose brown pasta, wholegrain bread and cereals, vegetables, fruit, fresh soups, smoothies and juices (not from concentrate), and eat a salad with every meal.

7. Slow things down. Eat slowly and chew properly. Chewing relaxes the lower stomach muscle and triggers nerve messages that activate the digestive process. If food is not properly chewed, nutrients remain locked in and undigested.

Keep portions moderate, and eat at regular times. If you find you're still hungry, wait 20 minutes for your brain to catch up with your stomach and recognise that you are full.

Your stomach and intestines are sensitive to stress. When you feel anxious, digestion will shut down, leaving food partially digested. So finding ways to manage stress is not only important for your emotional health, but your digestive health, too.

Note: If you suffer from heartburn, kidney or gall-bladder problems, or have a citrus allergy, consult your GP before going on this diet.