Obesity can lead to premature death and cause considerable ill health¹ and is one of the largest and fastest growing public health problems across the world. In England 17% of men and 21% of women are obese and over half the population is overweight. However, there seems to be more importance given to body image that ever before. For this reason many people, obese or not, are spending a considerable proportion of their income on information or treatments that claim to help tackle their "weight problem."

For the past 20 years the consensus of nutritional advice in the United Kingdom has been to eat less fat and more complex carbohydrates and fresh fruit and vegetables. But such an approach is often considered too simple, too boring, or too slow, and desperate people will often take desperate measures. Many of the books, products, and clinics available exploit the slimmer's desperation and obsession with weight, shape, and appearance by feeding them a succession of half truths and bogus science, claiming to assist in their attempts to lose weight. By buying into these fad diets many obese and overweight people have tried but failed to lose weight or maintain their weight loss but have spent a small fortune. Despite this, the enthusiasm for quick fix diets seems to be undiminished. Also, in such a climate opposing views on dietary strategies will always attract attention. Given the prominence of many of these alternative solutions, it is hardly surprising that the public is frequently confused by the apparent mixed messages.

Diet myths

The most popular dieting myths currently around are:

• The "detox your system" diets will not just cause weight loss but will banish cellulite and cleanse the body.
• Particular foods or combinations of foods such as those found in cabbage soup can boost metabolism and speed up weight loss.
• Poor digestion of foods or "allergy" to foods can cause weight gain.
• Protein containing foods and carbohydrate containing foods should not be eaten at the same meal.
• It is carbohydrates that are fattening and should be eliminated from the diet.
• Your blood group or any other physiological characteristics can dictate which foods you should and should not eat.

Diet myth No 1

Many celebrities are detoxing their system through diets that exclude wheat, dairy products, sugar, caffeine, and alcohol. This regimen will apparently cleanse your blood, flush out toxins, and so aid weight loss, and is claimed to be particularly effective in getting rid of cellulite. Cellulite is not a unique type of fat that requires special treatment and it is not caused by toxins. It is just a build up of fat in areas where people are predisposed to lay down fat. For women this tends to be the hips, thighs, and bottom, and nothing can change your genetic make up. Regular exercise and healthy balanced eating will eventually lead to weight loss but a few "wobbly bits" may still remain. Exercises targeted at specific muscle groups in problem areas are the best remedy.

Diet myth No 2

Soup diets promise a miraculous instant weight loss of up to ten pounds in the first week and attribute this result to the special combination of ingredients. Very often when people start to diet they find that they can lose a relatively large amount of weight in the first week. Then the weight loss slows down and they start to feel demoralised and often this is when they give up, only to repeat the cycle a few weeks later. There is no magic, rapid way that fat stored in our bodies can be lost. During the first week of a diet, especially an extreme diet such as fasting or very restrictive diets that eliminate most foods, people usually lose carbohydrate stored as glycogen, and the water that has been absorbed with it. We have approximately 500g of stored glycogen (that will last a sedentary person about three to four days) and each gram is stored with 3 g of water resulting in a 2 kg weight loss. Once this is lost, and if it is not replaced, fat loss will dominate, but being much more energy dense than carbohydrate (9 kcal/g versus 3.75 kcal/g), it requires a greater calorie deficit to be used up. There is no healthy way to lose weight fast.

There are no special combinations of foods that will affect the metabolism one way or the other. Overweight people do not usually have slow metabolisms, in fact quite the opposite. The bigger a person is, the harder the body has to work, for instance to pump blood around the body and carry the large frame when they move, so the higher the metabolism and the energy requirement. This means that a very large person can easily lose weight on 1500-1800 calories a day if they are only burning up 2500 calories. As they become lighter their calorie requirement will drop but this can be compensated by increasing the exercise level and lowering intake to maintain the deficit.

Diet myth No 3

People suffering from food allergies or food intolerances do not gain weight by eating the culprit foods, in fact quite the reverse, as food intolerances often cause sickness and diarrhoea or both. Food allergies can have very serious consequences resulting in anaphylactic shock; these milder reactions include asthma and eczema. None of these are pleasant but they are not responsible for weight gain.²

Dr William Hay invented "food combining" at the beginning of the last century. He believed that disease resulted from the accumulation of toxins and acid waste in our bodies. The way to cure disease was to avoid eating "foods that fight." In his opinion, you should not mix proteins and carbohydrates in the same meal, and you should eat foods which restore the body's natural balance between acids and alkalis. To date there is no scientific evidence to support this theory. The rules of food combining are rather complicated to observe and inherently contradictory, and the whole idea of food combining is nutritional nonsense. It is possible to lose weight observing the regimen but this is because it greatly increases the intake of fruit and vegetables at the expense of more calorific foods and also considerably restricts the types of food eaten (which may make it more difficult to meet nutritional needs). So while it is not harmful, people should not be fooled into thinking that food combining per se offers any nutritional benefit.

Diet myth No 5

In the high protein, low carbohydrate diet you are encouraged to eat all the meat, fish, eggs, and cheese you want, but have to cut out potatoes, bread, pasta, and fruit. Even the slimmer's favourite energy snack, the banana, is banned. The theory goes that it is sugar and not fat in the diet that makes a person fat. Sugar is rapidly absorbed into the blood stream causing blood glucose levels to increase. Insulin is then required to bring levels back to normal. Insulin also happens to be the hormone responsible for promoting

fat deposition. Up to here this theory is correct but irrelevant to dieters. By taking in fewer calories than are being used up, fat stores will be used as a source of energy. Not only do low carbohydrate diets go against all current healthy eating advice but they can lead to ketosis. This causes the pH of the blood to fall which can lead to unconsciousness and eventually coma. Anyone trying to exercise while following this diet will find it a real problem as stored carbohydrates are the best source of energy for exercise. This diet is likely to make the person feel tired, lethargic, and irritable.

Diet myth No 6

Diets based on the idea that a person's physiological characteristics, such as eye colour, hair type, or blood group, can dictate which foods are likely to cause weight gain have no scientific basis. The idea behind blood group diets is to split foods into groups of "highly beneficial," "neutral," and "avoid," depending on type.

For instance, people with blood group O are told to avoid sweetcorn as this will cause weight gain, whereas it is acceptable for those with a different blood type; people with blood group A are told kidney beans will encourage weight gain. Both sweetcorn and kidney beans are low in fat and high in fibre so it is difficult to understand why this should be the case. A person may well lose weight on this diet because it is so restrictive, but in being so is also likely to make the diet unbalanced. Daily consumption of fruit and vegetables of all types should be encouraged to help prevent diseases such as heart disease and cancer.

Blaming obesity on genes, metabolism, or mysterious outside forces does not help individuals to face up to the control they have over their own body weight. Acknowledging the contribution of personal lifestyle habits is an important first step in changing behaviour. It is of course possible to lose weight in any way that cuts energy intake below energy needs. However, the crucial long term goal requires a more holistic approach focusing primarily on health and not an unrealistic target body weight. Reducing dietary fat leads to a reduction in the risk of coronary heart disease; increasing complex carbohydrates helps promote a healthy gastrointestinal tract; higher intakes of fruit and vegetables may reduce the risk of some types of cancer. In addition, by eating a healthy balanced diet a person is more likely to achieve and maintain a healthy weight.

So, tell your patients, friends, and relatives to throw away the fad diet books and start eating a healthy balanced diet. The results might not be quick but at least it works in the long term.