Keeping to a healthy weight is important for your health. It can reduce your likelihood of developing a number of long-term health problems.
If you’re overweight or obese, it can increase your risk of developing conditions such as:
- coronary heart disease
- type 2 diabetes
- some types of cancer
- fertility problems (for women)
If you’re underweight, you may be more likely to develop conditions such as:
There are lots of ways to work out if you’re a healthy weight and if you’re at an increased risk of developing health problems. Common measurements are the body mass index (BMI) and the waist circumference and body shape.
BMI (Body mass index)
BMI takes into account your weight and height and is generally a good indicator of how much body fat you have.
To work out your BMI, use our BMI calculator. If your BMI is:
- less than 18.5, you’re underweight
- between 18.5 and 24.9, you’re a healthy weight
- between 25 and 29.9, you’re overweight
- between 30 and 39.9, you’re obese
- over 40, you’re morbidly obese
If your BMI is 25 or over, it’s a good idea to try to lose some of this excess weight. This helps to prevent you developing serious health problems. Your health is already at risk if you have a BMI of 30 or more.
Here is an example of the BMI measurement if you're five feet and three inches tall. You can see how your height might be the same as someone else but if your weight is different, your BMI category will change.
Here is another example of the BMI measurement, this time for a person who’s 5 feet and 10 inches tall. You can see how your BMI changes as you put on weight.
Limitations of BMI
BMI isn’t a suitable measurement for everybody. Here are some examples of people it doesn’t apply to.
- Pregnant women. BMI can’t be applied to you if you’re pregnant because you’re gaining weight because of your growing baby.
- Children. Their weight changes a lot as they grow, so their age and sex need to be taken into account too.
- People with a lot of muscle. Professional athletes and people who play a lot of sport may have a BMI of over 25 but have very little body fat.
- Ethnicity. If you belong to certain ethnic groups (for example, if you’re of Asian descent), the BMI ranges above may not be appropriate for you. See BMI and ethnicity below.
The BMI measurement doesn’t take into account your gender, age, or bone structure, which can all influence the relative amount of body fat you have. Yet despite these drawbacks, it’s the most commonly used test to check if you’re a healthy weight. BMI and ethnicity
The standard BMI ranges don’t apply if you belong to certain ethnic groups, for example, if you’re Asian. This is because if you’re of south Asian or Chinese descent, you have a higher risk of developing type 2 diabetes than white populations. You should aim to keep your BMI lower than the standard 25 to keep in good health – here are some cut off points.
- BMI of 23 – if you have a BMI score of 23 or more, you have an increased risk of getting type 2 diabetes.
- BMI of 27.5 – if you have a BMI of 27.5 or more, you’re at high risk of getting type 2 diabetes.
If you’re black, you should also aim to keep your BMI below 25. Although there is less evidence than for Asian people, this should reduce your risk of type 2 diabetes.
Body shape and waist circumference
Where you store fat on your body is an important indicator of whether or not your weight is a risk to your health.
If you store fat around your abdomen (tummy) and waist, when you’re said to be apple-shaped. This is thought to be worse for your health than storing it around your thighs and bottom (pear-shaped). If you’re apple-shaped, you’re at a higher risk of developing:
- coronary heart disease
- high blood pressure (hypertension)
Here’s how to measure your waist circumference properly.
- While you’re standing, put a tape measure around your middle – place it just above your hipbones.
- Make sure the tape measure is horizontal and around your waist.
- Keep the tape snug around your waist but don’t press it in.
- Breathe out and measure your waist.
Your health may be at risk if you have the following measurements.
- Men: a waist measurement of 37 inches (94cm) or more (if you’re south Asian, it’s 35 inches or more, which is 90cm).
- Women: a waist measurement of 32 inches (80cm) or more (this also applies to Asian women)
If you’re not sure whether you’re a healthy weight, check with your practice nurse at your GP surgery.
Your weight is determined to some extent by your genetics and how easily you put on weight. But it’s also determined by the balance between what you eat and drink, and how active you are. The energy that food provides, which you use up walking, running or even sitting still is measured in calories.
- You will gain weight if you take in more calories than you use up.
- You will lose weight if you use up more calories than you take in.
- You will maintain your weight if you balance the calories you take in with the calories you use up.
But what does this mean for you, and what changes can you make if you weigh too much or too little?
If you’re a healthy weight
This is great news but keep it up! Aim to maintain your weight through a combination of eating a healthy, balanced diet and regularly doing some exercise. This will help to keep you in good health and feeling your best.
Don’t skip meals as you will be tempted to over-compensate later. Instead, eat regular meals, especially breakfast, and make sure your portion sizes are about right. For information on what a healthy diet looks like, see our information on diet and nutrition.
Try to do some physical activity every day and try to spend as little time as possible being inactive.
It’s a good idea to check your weight every now and then – ideally every week – so you know you’re still on the right track.
If you’re overweight or obese
Your risk of health problems such as heart disease, diabetes and cancer is higher if you’re even a little overweight. And the more overweight you are, the greater your risk of these diseases. This risk increases even further if you don’t do any physical activity.
If you lose excess weight and get active, it will really benefit your health. To put it simply, to lose weight you need to burn off more calories through physical activity than you take in from food and drink. The best way to do this is to increase how much exercise you do and reduce how much you eat.
If you don’t currently exercise, our article Exercise – getting started can give you plenty of tips. Walking is a great introduction to getting more active.
As well as exercising, it’s also important to eat a healthy, balanced diet and cut down on foods that contain fat and sugar. Check the labels of food carefully to ensure you don’t eat too many of these. Another element that often catches people out is the calories they consume from drinking sugary drinks. Water is the best option and it needn’t be boring as there are lots of ways you can make it interesting - find out how with our Keeping hydrated article.
Remember, you will start to improve your health even if you lose only a bit of weight.
If you’re underweight
There are lots of reasons why people can be underweight. These include mental health conditions, such as anorexia nervosa, for example. You may also be at risk of malnutrition if you have a long-term medical condition such as cancer or chronic obstructive pulmonary disease (COPD). If you’re older, you can become underweight through not eating enough. You may find it difficult to prepare or eat meals, or have a reduced appetite, for example.
If you have a very restricted diet, you might not be getting all the nutrients, vitamins and minerals that your body needs to be healthy. This can lead to health problems such as heart arrhythmia (palpitations) and osteoporosis. It may even lead to mental health problems. Our feature Does your diet impact your mood? explains more about this.
If you’re underweight, try to increase your calorie intake through eating a balanced and nutritious diet. This way, you gain weight and get back into a healthy weight range for your height. Eat regular meals and snacks and start your day the right way with a healthy breakfast. Also make sure your portion sizes are about right. If you’re finding it hard to do this, ask your dietitian or GP for advice.
Unexplained weight loss, or inability to put on weight, can sometimes be a symptom of an underlying health problem. If you have concerns about weight loss, contact your GP.
- Maintaining a healthy weight and preventing excess weight gain among adults and children. National Institute for Health and Care Excellence (NICE), March 2015. www.nice.org.uk
- What are the health consequences of being overweight? World Health Organization. www.who.int, published March 2013
- Fertility. National Institute for Health and Care Excellence (NICE), February 2013. www.nice.org.uk
- Anorexia nervosa. BMJ Best Practice. www.bestpractice.bmj.com, published 6 February 2015
- Palpitations. PatientPlus. www.patient.info/patientplus, reviewed 18 February 2014
- Obesity in adults. BMJ Best Practice. www.bestpractice.bmj.com, published 14 October 2014
- Briefing note: obesity and life expectancy. National Obesity Observatory. www.noo.org.uk, published August 2010
- Managing overweight and obesity in adults – lifestyle weight management services. National Institute for Health and Care Excellence (NICE), May 2014. www.nice.org.uk
- Assessing body mass index and waist circumference thresholds for intervening to prevent ill health and premature death among adults from black, Asian and other minority ethnic groups in the UK. National Institute for Health and Care Excellence (NICE), July 2013. www.nice.org.uk
- Need to lose weight? Weight Wise. www.bdaweightwise.com, published 2013
- Assessing your weight. Centers for Disease Control and Prevention. www.cdc.gov, published 15 May 2015
- Improving your eating habits. Centers for Disease Control and Prevention. www.cdc.gov, published 15 May 2015
- Abnormal weight loss. PatientPlus. www.patient.info/patientplus, reviewed 25 September 2014
- Osteoporosis. Medscape. www.emedicine.medscape.com, published 26 February 2015
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Reviewed by Rachael Mayfield-Blake, Bupa Health Content Team, September 2015.
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