Controlling your Weight

Maintaining your weight within a healthy range for your height

An essential part of a healthy lifestyle is maintaining your body weight within the range considered normal for your height. In recent decades, the number of overweight and obese people (including children) in many developed countries has increased significantly. In the UK, an estimated 1 in 4 adults (see Obesity in adults) and 1 in 5 children (see Obesity in children) are obese.

Excess weight amounting to obesity is a major threat to health. Disorders associated with being obese, such as coronary artery disease, high blood pressure (see Hypertension), cancer, and stroke, rank among the leading causes of illness and death in developed countries such as the UK. Being underweight can also cause health problems, including an increased risk of infertility and the bone disorder osteoporosis.

Causes of weight problems

In the UK, the main factor contributing to the general weight gain of the population is lack of exercise combined with overeating. Children’s pastimes are far more sedentary than those of former generations, and many adults do not exercise at all. In addition, an increasing number of people rely on convenience foods, which tend to be high in saturated fat and simple carbohydrates, both of which are high in calories.

There are various reasons why someone may be underweight. Some people are naturally thin and find it difficult to gain weight no matter what they eat. Others start within the normal weight range but then develop an eating disorder, such as anorexia nervosa or bulimia, and lose a great deal of weight, eventually becoming abnormally thin. Weight loss can also result from loss of appetite due to long-term illness such as depression, tuberculosis, or rheumatoid arthritis.

Finding your ideal weight

Height and weight charts offer a quick and easy way to find out whether you are within the recommended weight range for your height. Your ideal body weight depends on both your height and on the amount of muscle tissue you have. For example, an athlete should weigh more than a healthy but relatively sedentary person of the same height. This is because exercise increases muscle, which is heavier than other types of body tissue. For this reason, the charts provide healthy ranges for height and not precise measurements.

Recent research indicates that the distribution of fat around the body is an important determinant of health. Excess fat around the abdomen is more closely linked to cardiovascular diseases than fat elsewhere in the body. To find out whether you are a healthy weight, you should both check if your weight falls within the recommended range for your height and measure your waist size (see Are you a healthy weight?).

Doctors and dieticians use weight and height measurements to calculate body mass index (BMI). This is a widely accepted and more precise method of checking if you are underweight, a healthy weight, or overweight by providing an indication of the degree of fatness, although it is not a direct measure of body fat. The BMI is calculated by dividing a person’s weight (in kilograms) by his or her height (in metres) squared. A BMI of 18.4 or less is classed as underweight; 18.5–24.9 is classed as a healthy weight; 25–29.9 is classed as overweight; and a BMI over 30 is classed as obese. These BMI figures are general ones that apply to most healthy adults under 60. They are not applicable to children or people over 60; those with chronic health problems; women who are pregnant or breast-feeding; or athletes, weight-trainers, or similar groups of people with a high proportion of body muscle.

Body mass index is also used to check whether children are a healthy weight or not, although the BMI value is used in a slightly way from how it is used in adults. A child’s BMI is plotted on a chart and compared with how it relates to the BMI values of children of the same age.

Losing weight

If the height/weight chart confirms that you are overweight, you can lose excess weight by following a slimming diet and taking exercise. In rare circumstances, a doctor may advise drug treatment or surgery as well as a slimming diet to aid weight loss in a very obese person.

Before you attempt to lose weight, you should try to identify why you may be overweight. The most likely cause is a combination of overeating and lack of exercise, but you may find it helpful to look at your reasons for overeating. For example, do you tend to eat when you feel unhappy or is overeating a habit that has become established in your family?

The best way to lose weight is to combine calorie reduction with regular exercise. Plan what you need to do to succeed. For example, if you need more exercise, arrange a time each day to take a brisk walk. If you are tempted by the wrong foods, make a list of healthy foods before going to the supermarket.

Success in dieting also depends on being realistic about how much weight you can lose. Set yourself a practical, short-term target, revising it as you go along. About 2–4 kg (4.5–9 lb) a month is sensible. If you want to lose more than this or have any health problems, consult your doctor before you start.

You also need to consider what you hope to achieve by losing excess weight. It is important for you to accept that weight loss may not solve all your problems. It may make you feel better and more confident, will certainly improve some aspects of your health, but it is unlikely to help a failing relationship or make you more popular. However, the health benefits are worth any effort and lifestyle changes you may have to make.

Slimming diets

If your diet does not provide you with enough calories for all your energy needs, your body will start to use up excess fat as an energy source. Therefore, you should begin to lose weight if you make changes to your diet to include fewer calories than before. Publications that list the calorie content of a variety of foods, both natural and processed, are widely available, and this information can also be found on the labels of most packaged food (see Understanding food labels). A good starting point for most people is to try to reduce their daily calorie intake by about 500 calories. This can be achieved by cutting down on high-fat foods, such as cakes, pastries, cheese, and fried dishes, and replacing them with healthy, low-calorie foods, such as fruit, vegetables, and grilled dishes.

If your normal diet already consists mainly of low-calorie foods, you simply need to cut down on the quantity of food you eat. The best type of slimming diet is one that is low in calories but balanced so that you stay well nourished (see Healthy eating).

Alcohol contains no healthy nutrients and is high in calories. It is therefore advisable to reduce your alcohol consumption as much as possible when you are trying to lose weight.

Rapid weight-loss plans (see Fad diets) and fasting to lose weight should be avoided. They can damage your health by depriving your body of the range of nutrients it needs to function well. Such plans do not produce sustainable weight loss or encourage sensible, healthy eating habits.


Exercising to lose weight need not be strenuous, but it does have to be regular. Sustained regular exercise raises your basal metabolic rate (BMR), the rate at which your body uses energy to maintain basic processes such as breathing, digestion, and the heartbeat. If your BMR rises, you use up more calories (see Exercise and health) and will lose weight if you also follow a calorie-controlled diet. Exercise tones and builds muscles, which weigh more than fat. Therefore, as you become fitter, you may find that the scales initially register a few more kilograms, although you will not actually be any fatter. Exercise can also stimulate your appetite; you must resist eating more than your new diet allows. As you become older, your metabolism slows down, and therefore your body uses up fewer calories. It is important to remain as active as possible to prevent the gradual weight gain that is common among older people.

Drugs and surgery

Weight-reducing drugs are usually recommended only for people who are obese and for whom exercise and diet alone has not helped, especially if they also have other risk factors to health, such as diabetes mellitus and/or high blood pressure. Weight-reducing drugs are always used in conjunction with diet and exercise and should not be taken long term.

Certain drugs for weight loss are available over the counter, such as bulking agents and orlistat (Xenical). Bulking agents, such as methyl cellulose, make you feel full but may cause bloating and flatulence. Orlistat inhibits the absorption of fat in the intestine; possible side effects include headaches, flatulence, an urgent need to defecate, an oily discharge from the rectum, and liquid or oily faeces.

Generally, surgical procedures for weight loss, such as gastric banding, are considered only as a last resort and only for people who are extremely obese.

Gaining weight

Many people think that being underweight is not a health risk. It can be just as unhealthy as being overweight and requires careful treatment. If your BMI is 18.4 or less and if you have other symptoms, such as excessive tiredness and an inability to keep warm, you should see your doctor to exclude an underlying condition that requires treatment.

It is important to gain weight sensibly to build up muscle and bone and achieve a healthy level of body fat. Although fatty and fast foods are high in calories, you should avoid eating large quantities to gain weight because of their unhealthy effects, such as causing high blood pressure and increasing risk of heart disease. Put on weight slowly by eating a healthy, balanced diet. Several small, nutritious meals each day provide a better supply of energy than one or two large meals.

Regular exercise helps to build muscles, increases strength, and may also improve your appetite. You should start slowly, especially if you tire easily, and build up the amount you do gradually.

Assessment: Are you a Healthy Weight?

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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