However, in the first days of the plan you may eat nothing but low fat protein foods for several days. This is called the ‘attack’ phase and it lasts for 5 days for most people, although it can be from 2 to 7 days depending on your starting weight and circumstances.

In the attack phase you can eat lean meats, skinless chicken, turkey and fish, eggs, tofu and seitan, plus fat free dairy products. You must also have 1.5 Tbsps oat bran for fiber, which most people eat beaten with eggs in a pancake or omelet. You don’t eat anything else – no vegetables, cooking fats, fruit, rice, bread, nuts, alcohol, etc.

After your few days in the attack phase, you move to ‘cruise’. This is the ongoing weight loss plan that you will follow until you reach your ‘true’ weight, which depends on your starting weight and may be higher than your ‘ideal’ weight. In this phase half of your days will be protein days where you follow the ‘attack’ plan, and the other half will be days when you can add non-starchy vegetables to the mix. You can do this on alternate days or have 2-5 days of one plan followed by the same number of days on the other.

During this time you still do not eat any of the other foods, i.e. cooking fats, fruit, rice, bread, nuts, alcohol, etc. Many of these foods are added back in the final ‘consolidation’ phase, although they are still limited and you will still have one ‘attack ‘ day per week.

The consolidation phase lasts longer than the cruise phase, being 5 days long for every pound lost. So if you lost just 20 pounds, which you might do in 1-2 months, your consolidation phase would be 100 days long, i.e. over 3 months. Also, you might still lose weight during this phase, so do not despair if your ‘true weight’ was higher than you wanted to aim for. You could still reach your target in the consolidation phase.

Finally, phase 4 is the permanent stabilization or maintenance phase. You will still have one pure protein day per week and take oat bran, but otherwise you can eat a normal diet.

On the Dukan diet it is vital to drink at least 5 pints of water a day, or your health will suffer. You should also be getting some exercise every day, even if it is just a short walk at first.

If you are concerned about getting enough nutrients on low fat low carb diets, you should definitely take vitamin and mineral supplements. Dr Dukan does not stress this because the attack phase is so short, but if you have a lot of weight to lose you might not be getting enough of some of the vitamins that are found mostly in higher carb foods, so supplements would be a wise precaution.

Low carb low fat diets are not easy to stick to. One of the things that made the Atkins plan so popular was the fact that a high fat content keeps us feeling satisfied, so we eat less. If you are often hungry, you are likely to eat more and be tempted to drift away from the plan, especially if it is very restrictive.

Another issue with this type of diet is that a lot of people just do not like to eat that much meat. This may be partly cultural: if you come from a high meat eating background, you may be happier on the Dukan Diet than some others.

Low fat low carb diets have also had some criticism from mainstream health professionals for its high quantities of protein, which could be a stress on the liver and kidneys. Dr Dukan says that his diet should not harm somebody who has healthy organs provided they drink plenty of water, but nobody with an existing liver or kidney disease or condition should attempt it without advice from their own physician. In fact, it is wise to talk to your doctor before starting any weight loss program, especially low fat low carb diets.

South Beach follows the same structure as the Atkins diet with a two-week induction phase followed by an ongoing weight loss phase and finally, maintenance. However, the foods allowed in the different phases are not all the same.

The South Beach diet is based on the glycemic index of foods. This is a measure of how fast the food converts to glucose in our digestive system. Sugar and refined flour convert very fast so they are high on the glycemic index and not allowed on the South Beach low carb weight loss plan. Middle range foods are restricted and may not be allowed in the first two weeks of the plan.

So what can you eat during phase 1 of the South Beach low carb weight loss program? Lean beef, chicken and turkey breast are allowed in unlimited quantities, but fatty meats and skin are not allowed, to reduce the amount of saturated fat.

However, you can have healthy oils including olive oil and mayonnaise. You can also eat non-starchy vegetables, peas and beans, seafood, eggs, low fat cheese and a small amount of nuts. With this range of foods, the South Beach diet is probably the best low carb weight loss plan for vegetarians.

Foods not allowed during induction include regular cheese, sugar, potatoes, rice, pasta, alcohol, fruits and starchy vegetables. Most of these are added back in limited quantities in phase 2.

One of the best things about a low carb weight loss diet is that you can eat as much of the unlimited foods as you want. Unlike calorie controlled diets, you should never feel hungry, even in phase 1 of the program. You get to eat five times a day, with three meals and two snacks.

You may have some cravings for particular foods but these will pass after a few days. You will find it easier if you are able to clear your kitchen of the foods that you should not be eating. If others in your household still want high carb foods and snacks, keep them in a special place where you do not go.

So how much weight can you expect to lose on the South Beach diet? A lot depends on you, but people have had losses of up to 15 pounds in the two weeks of phase 1, followed by steady losses of up to 2 pounds per week on average after that.

As with all diets, your losses in the first phase will depend on what you have been eating before. If you have been following a very unhealthy diet with a lot of sugar, salt and alcohol, your body probably has a lot of retained water that will be lost quickly in the first 7-10 days of the diet, so the scales will show a big loss.

But if you have been following a healthy diet before, your losses will be less, because your body does not have that retained water to lose. If you understand this, you will not be disappointed if your loss is less than other people’s. A low carb weight loss plan could still be just as effective for you in the long term.

If you are thinking of following the Atkins diet you will need a copy of ‘Dr Atkins’ New Diet Revolution’. This is the revised version of his diet which includes more vegetables and is generally felt to be a healthier diet to follow than his first plan, so be sure to buy the book that includes the word ‘New’ in the title.

Atkins and other low carb dieting plans work by keeping your carbohydrate consumption low enough that you enter ‘ketosis’ or ‘lipolysis’. This is a natural condition of the body designed to deal with times when carbohydrate foods are scarce.

Many body functions require glucose for energy, and normally this is taken from the carbohydrate foods that we consume. But if the body is not getting enough of these, it can switch to using fat for energy. In this state it will use both the fat that we consume and the fat that is stored in the body, so we lose weight.

Unlike some other low carb dieting plans, the Atkins diet does not restrict fat consumption. This is because the switch to lipolysis depends on the body having plenty of fat in the diet as well as using stored fat. Also, fat is a substance that makes us feel full for a long time after eating. In fact, Dr Atkins included a rule that says you must not go more than 6 hours between meals, simply because his first patients found they were not hungry, and were not eating enough.

So what are the rules of the Atkins way of low carb dieting? Well, there are three stages. The first and best known is induction, in which you are restricted to a maximum of 20 grams of carbohydrate.

Some people assume that this means that you can have 20 grams of pasta a day, but that is not the case at all. Almost all foods contain carbohydrate, except for meat, fish and oils. So if you are counting the carbs in your food, you need to do it by using an online diet tracking program such as fitday.com.

For those who do not want to weigh and record everything that they eat, Dr Atkins gives you a list of foods that you can eat freely (e.g. meat, fish, oils) plus foods of which you can eat a certain amount each day (e.g. milk and dairy products, avocado). In addition you get to eat up to 3 cups of vegetables a day, which you take from certain lists. These do not include starchy vegetables like carrots and potatoes, which are not allowed on induction.

If this sounds restrictive, do not worry. You only follow induction for 2 weeks to kick start your weight loss. Then in phase 2 you will gradually increase your carbohydrate intake and at the same time, reintroduce some of the foods that were not allowed during induction. This means more vegetables, including some beans and starchy vegetables in small quantities; more dairy products; nuts, fruits, whole grains and even alcohol.

Phase 3 of the Atkins low carb dieting plan is maintenance for when you have achieved or almost achieved your desired weight loss.