Very low calorie diets became very popular in the 70's and 80's with shake diets as low as 330 calories per day and the famous Cabbage Soup Diet, which supplied a very low amount per day. When you reduce your calorific intake to such a low level a number of things happen to your body.

As the body initially believes that food is now in short supply, the first energy sources that the body will use are easily available short-term energy stores in the liver. As these contain a large amount of liquid, many people will find that this results in a weight loss of up to 6 pounds in the first few days. However, none of this weight loss will be fat at this stage.

Once the short-term energy sources are used, the body begins to use its other stores for energy. Unfortunately, your body cannot store protein in the same way that it stores fat. Protein is very important for the body as it is used in a number of functions including the use and repair of muscles. When your protein intake drops below the body's requirements, the body will look for whatever protein it can find, and one source is the muscle itself. The body will literally begin to 'eat' itself to obtain the protein that it requires. The body will also begin to break down fat stores, however the body is only able to metabolise a certain amount of fat per week. Some scientists have calculated this as 2-3 pounds of fat per week. If your calorific requirements are higher than this, the body will again use whatever stores it has to call upon, which will include lean muscle tissue.

The long-term effects of a very low calorie diet are devastating to the body. As the amount of muscle in the body 'sets' your metabolic rate, as the muscle is eaten by the body, the metabolic rate drops. This will mean that weight loss will slow, sometimes encouraging the dieter to reduce their calories even further. It will also mean that when you raise your calorie level again to a normal level, weight gain will be faster and you may even end up heavier than when you began dieting! Hence the yo-yo dieting that we are all so familiar with! It is also very hard to ensure that you get an adequate supply of all the correct vitamins and minerals on a low calorie diet, so many people find that their hair nails and skin all show signs of deterioration. A lack of certain minerals like calcium can even result in loss of bone density and osteoporosis in later life.

So how can you avoid these problems whilst still maximising your weight loss? The first thing to ensure is that the body has everything it needs so it does not need to call on energy sources other than your fat reserves. Eat a well balanced diet with lots of fruit and vegetables and if you have any doubts that you are getting enough vitamin make sure you take a good quality multi-vitamin and mineral supplement. You should also make sure that you eat an adequate amount of protein. Many nutritionists in the US now suggest eating 40% carbohydrate, 30% protein and 30% fat, and this is a good ratio to follow.

You should always make sure you never eat less than 20% of your calories as protein. Good sources of low calorie protein include chicken, fish and quorn. If you are incorporating exercise into your programme, you may wish to raise the level of protein you eat, as the repair process of your muscles will require protein. Recent studies have indicated that people on high protein diets lose weight at the same rate as people on high carbohydrate diets, but maintain their metabolic rate, thus maintaining their weight loss better.

Your calorie intake should be kept above a certain level to ensure that you lose weight safely, burning fat as energy rather than muscle. Aim to eat around 1,200 - 1,500 calories per day if you are a woman and 1,800 - 2,100 calories per day if you are a man. Never go below 1,000 calories per day. If you lose weight at the rate of 1-2 pounds per week, you can be sure that it is fat you are losing.

Trying to make sure you exercise, as part of your programme will also help to make sure you do not lose muscle. Try to build a couple of sessions of resistance or weight training into your programme each week. Some studies have indicated that doing muscle exercise minimising muscle loss even in low calorie diets, and by building your muscles you will be increasing your metabolic rate too!