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Healthy weight for adults

This factsheet is for people who want to know more about maintaining a healthy weight.

The UK population is getting fatter - the number of people who are obese has tripled since 1980. Currently over half of women and around two thirds of men in the UK are either overweight or obese.

What are the risks of being overweight?

Being overweight increases your risk of developing health problems such as heart attacks, strokes, diabetes, high blood pressure and some types of cancer. Excess weight also makes arthritis more likely and can make breathing and sleeping difficult.

The more overweight you are, the more likely you are to have health problems.

What causes obesity?

A calorie is a unit of energy. You take in energy when you eat and drink, and burn it off in your daily activity. When the amount of calories in the energy you eat and drink equals the amount you burn off, your body weight remains about the same. You can become obese if you consistently eat more calories than you burn off.

Obesity does run in families, and the tendency to put on weight is greater in some people than in others eating a similar diet. But it is likely that family eating and activity habits are more important causes of obesity.

Guidelines for a healthy weight

The most common benchmark of healthy weight for adults is based on height and weight, and is called body mass index (BMI).

BMI is a good indicator of the total amount of body fat, and it can be used to predict your likelihood of having a disease associated with being too heavy (or too light).

BMI is calculated with the formula:

BMI = weight (in kg) divided by height² (in m)

To work out your BMI, divide your weight in kilograms by your height in metres, and then divide the figure you get by your height in metres again. Or use our website BMI calculator.

Understanding your BMI

Underweight (BMI less than 18.5)

Some people in the underweight category (BMI under 18.5) are naturally lean and healthy. But being underweight can be bad for your health. If you are in the underweight category and have been restricting your diet, you should aim to gain weight and get back into the normal weight range for your height. If you are finding it difficult to put on weight, or you lose a lot of weight rapidly, you should see your GP.

Healthy weight (BMI 18.5 - 24.9)

If you are in the healthy range (BMI 18.5-24.9) for your weight and height, you should aim to maintain your weight through a combination of healthy diet and physical activity. Don't be tempted to try to get into the underweight category.

Overweight (BMI >25 - 29.9)

If you are in the overweight (BMI 25 - 29.9) range you should concentrate on not gaining any more weight. Try to cut down on sugary and fatty foods and on the amount you eat to get back into the normal weight range for your height. Increasing your levels of physical activity will help.

Obese (BMI >30 - 39.9) or morbidly obese (BMI > 40)

If you are in the obese (BMI 30 - 39.9) or morbidly obese (BMI over 40) range then your risk of health problems is high. It is important that you try to lose some weight and should consider asking for help from your doctor. "Morbidly" obese means that the amount you are overweight is harmful to your health.

Limitations of BMI

BMI doesn't apply to everybody. If you have a lot of muscle, you may have a BMI over 25 but very little body fat and be a healthy weight. Similarly, if you have very little muscle, you may still have too much body fat, even though you are in the correct weight range for your height.

BMI does not apply to pregnant women, children or some ethnic groups (eg a BMI of 27.50 for an Asian person has been shown to have a health risk the same as a BMI of 30 for a white Caucasian person).

Body shape

Where the fat is stored on your body relates to the risk to your health. Carrying fat around the middle of your body, giving your body an "apple shape", is a greater risk to your health than carrying it around your bottom and thighs, which gives you a "pear shape".

Measuring your waist also gives a rough guide to whether you need to lose excess weight. An at-risk waist measurement is 102cm (40 inches) for men and 89cm (35 inches) for women.

If you are under 150cm (4ft 11 inches) tall, a smaller measurement will apply. Ask your GP or practice nurse for advice if you are worried about your weight.

Body composition

Measuring how much of your body weight is made up of fat and muscle can be a useful way of monitoring your weight. The amount of fat in your body, not your total weight, determines your health risk due to being overweight. A dietitian at your nearest BUPA hospital, or your local gym or leisure centre, may be able to arrange a body composition test. The usual methods of measurement are:

• skin-fold callipers
• bio-electrical impedance - electrodes are placed on your skin and a painless electric current is passed through your body

How can I lose excess weight?

In order to lose excess weight, you need to burn off more calories through physical activity than you take in from food and drink. This means tipping your energy balance by eating fewer calories, burning more off or, preferably, both.

If you have a lot of weight to lose, it's better to set a realistic medium-term goal, rather than aiming to lose a large amount of weight (eg 50kg). Doctors often suggest that you start off with a goal to lose 10 percent of your weight in about three months. Once you've achieved this, you can set yourself a new goal.

Choosing a diet

Some diet programs and adverts promise a "quick fix" of rapid weight loss. These are often unscientific, and may be harmful. Reducing your calorie intake drastically won't help you to lose weight, as your metabolism will slow down to conserve calories for your body's internal functions (such as breathing and digestion).

The challenge is not just getting to, but maintaining a healthy weight in the long term. Avoid crash diets and fad diets, and if you want to follow an organised diet program, look for one that:

• only promotes gradual weight loss of 0.5 to 1kg (1 to 2lbs) per week - any more than this and you'll be losing water and muscle, not fat
• encourages you to follow the guidelines for healthy eating - a balanced, varied diet that incorporates all major food groups
• is realistic and flexible enough that you can stick to it - no extreme hunger and no bans on certain foods
• encourages you to be more physically active
• helps you to learn new lifestyle habits and ways of thinking about food, so you can maintain your target weight once you have reached it

Making your own changes

You can also lose weight by making your own changes to your daily diet and exercise patterns. The best way for most people to lose weight is to combine more physical activity with a diet that is lower in calories. In general you should aim to reduce the number of calories in your food and drink to 1,000 to 1,500 calories per day, depending on how overweight you are. If you are unsure about the different calorie content of foods and meals, there are many recipe books available that contain this information.

Tips for controlling calories

• Keep a food diary for a week, writing down everything that you eat and drink. People who are overweight often don't realise how much they are eating.
• Use your food diary to find ways of cutting down calories. For instance, you could cut 500 calories per day by changing the balance of foods on your plate, eg less cheese and more salad with your dinner. Or you could cut out a regular snack food and replace it with a piece of fruit.
• Don't forget that drinks count towards your daily calorie intake. Alcohol is high in calories - three pints of beer could add up to 600 calories and a large glass of wine can provide about 135 calories. You should also limit sugary drinks, because apart from the energy, they have virtually no nutritional value.
• Aim to do 30 minutes of moderate physical activity on most days of the week. Moderate activity is where you feel slightly warm and out of breath - brisk walking is ideal.

Medical help

There are medicines that your doctor can prescribe to aid weight loss in combination with a low-calorie diet. These are generally only prescribed for people with a BMI of over 30.

For severe obesity (BMI of over 40), surgery to bypass the stomach or to make it smaller, may be an option if other weight-loss methods have failed. Your GP will be able to give you more information on these options.

Further information

• Food Standards Agency
  www.foodstandards.gov.uk
• British Nutrition Foundation
  www.nutrition.org.uk

Sources

• Food Standards Agency
  www.eatwell.gov.uk
  accessed 6 September 2006
• Obesity and overweight. World Health Organisation.
  www.who.int/en
  accessed 6 September 2006

Published by BUPA's health information team, healthinfo@bupa.com, December 2006.

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