Why is being a healthy weight important?

Carrying too much or too little weight can increase your risk of developing a range of health problems. There are some simple but effective steps you can take that can help you to manage your weight.

There can be confusion about what a 'healthy weight' is. Doctors and medical scientists use words such as 'overweight', 'obesity' and 'underweight' to describe weight levels that have been shown to increase the risk of health problems. A healthy weight is one that is associated with a low risk of health problems. It will vary from person to person.

Health problems related to being overweight or obese

Generally speaking, the more extra weight a person carries, the greater the risk is that they will also develop a range of other serious health conditions, particularly if they are obese.

These can include:

Health problems related to being underweight

Being underweight can also increase the risk of health problems. Because the body may not be receiving all the nutrients it needs, underweight people can be at an increased risk of:

  • Developing some infectious diseases (because the immune system may be impaired);
  • Developing osteoporosis later in life;
  • Having decreased muscle strength;
  • Digestion problems;
  • Fertility problems in women, and;
  • Experiencing hypothermia in cold weather.

Eating disorders such as anorexia nervosa and bulimia nervosa can contribute to a person being underweight and may be life-threatening if they cause extreme levels of underweight.


A feeling of tension, nervousness and dread about future events. It can trigger physical symptoms such as a rapid pulse or breathing difficulties.


The process of breaking down food so that it is easier for the body to absorb nutrients.

Eating disorders

A problematic eating habit that negatively affects a person's physical and mental health.


Relating to the internal lining of the uterus.

Gall bladder

A small organ attached to the liver that stores bile until it is released into the small intestine, to aid the digestion of food.


A serious condition that occurs when the body temperature falls too low, usually due to exposure to cold and damp conditions. Symptoms include uncontrollable shivering, drowsiness and confusion. It requires emergency medical treatment.


A large, internal organ of the body, located on the upper right-hand side of the abdomen. The liver has hundreds of distinct functions, including producing bile, regulating the body's metabolism and detoxifying the blood.


Substances in foods that are necessary for the body to function and grow. They include macronutrients, which provide energy and micronutrients, which are substances needed in small amounts such as vitamins, minerals and trace elements.


Relating to the pancreas, an organ located in the abdomen that secretes important chemicals, such as insulin, into the bloodstream and digestive enzymes into the intestines.

Measurement of weight

There are a number of measures that can be applied to determine whether a person's weight may cause health problems. Two of the most commonly used are:

  • Body mass index (BMI), and;
  • Waist circumference.

Body mass index

BMI is a tool that is used to classify the weight of adults into healthy, overweight and obese. BMI is also used to classify the weight of boys and girls aged 2-18, but it is interpreted differently to adults.

It is recommended by the World Health Organization and used as the main measurement in many guidelines for obesity around the world.

Your BMI is calculated by dividing your weight (in pounds or kilograms) by your height (in inches or meters) squared described in more detail below.

Pounds and inches: Formula: weight (lb) / [height (in)]2 x 703
Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.
Example: Weight = 150 lbs, Height = 5'5″ (65″)
Calculation: [150 ÷ (65)]2 x 703 = 24.96
Formula: weight (kg) / [height (m)]2

Kilograms and meters (or centimeters): With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Because height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters.
Example: Weight = 68 kg, Height = 165 cm (1.65 m)
Calculation: 68 ÷ (1.65)2 = 24.98

BMI score

Weight range




Healthy weight





It is important to remember that the BMI is an approximate guide and is not accurate for everyone. One reason for this is that people with the same weight can carry different amounts of fat compared to their lean body mass (bone and muscle).

Also, BMI does not take into account where body fat is accumulated on the body. Not all body fat contributes equally to health problems. Fat underneath the skin, particularly on the hips and thighs, does not tend to cause as many problems as fat around your abdomen. In particular, fat that builds up around the organs inside the abdominal cavity can cause inflammation within the body and contributes to many of the health problems associated with carrying extra weight.

At any given weight, different people will carry varying amounts of fat around their abdomen. People from some ethnic groups can tend to carry more fat around their abdomen. For this reason, waist circumference, which can be a good indicator of how much abdominal fat a person is carrying, is also often used to assess how much of a risk a person's extra weight may pose to their health.

Waist circumference

To measure waist circumference with a tape:

  • Stand straight with feet about 15cm apart and breathe normally;
  • Place the tape directly on skin (remove any bulky clothes before measuring);
  • Place a tape horizontally around the waist at around the level of the bellybutton (halfway between the bottom of the ribs and the top of the hip bones), and;
  • Breathe out (no holding your breath or sucking in your stomach) and take the measurement.

For men, a waist circumference of 94cm or greater is associated with increased risk of health problems. For women, it is a waist circumference of 80cm or greater.

Male measuring his waist circumference.Your waist circumference can be a good indicator of health risks from extra weight around the abdomen. 


The part of the body that lies between the chest and the pelvis.

Energy and weight

Energy in

Energy in food is measured in kilojoules or calories (1 calorie = 4.2 kilojoules). Foods vary in the amount of energy they provide. For example, vegetables tend to be low in energy and high in dietary fiber and nutrients that the body requires. Foods that contain a lot of carbohydrates and fats tend to be high in energy.

Beverages also contribute to energy intake. While water contains no energy, soft drinks, fruit juices and alcoholic beverages are all high in energy.

The portion size of the foods you eat is also important. Even foods with moderate amounts of energy can contribute to weight gain if they are eaten to excess.

Energy out

Metabolism describes the chemical processes that occur inside the cells in your body in order for the body to function. These processes require energy and this is called your basal metabolism.

Physical activity also uses up energy. The more vigorous the exercise (such as running), the more energy the body will use, although all activities - such as housework, walking to the shops and even standing still - contribute to the amount of energy the body uses every day. With high-energy foods, you can take in large amounts of energy very quickly, while it takes much more time and effort to work off that energy.

Control of body weight

Taking in small amounts of extra energy on a daily basis can eventually add up to carrying quite a lot of extra weight if you do it over a long period of time. However, the way the body regulates weight is quite complex. It involves a system of hormones in the body (including insulin, leptin and ghrelin) that:

  • Increase hunger;
  • Decrease appetite and food intake, and;
  • Increase metabolism and the amount of energy the body expends.

Generally speaking, this system works to try to maintain body weight at the same level over time. This level is sometimes called a set point. When your weight increases or decreases from your set point, the hormones will try to work together to get your weight back to that level.

When a person gains a lot of weight, the body can change the set point to a higher level, which is one reason why it can be difficult to lose excess weight once it has been gained. This is another good reason to manage your weight and keep it in the healthy range if you possibly can.


The fundamental unit of life; the simplest living unit that can exist, grow, and reproduce independently. The human body is composed of trillions of cells of many kinds.

Dietary fiber

Ingredients in food that are not digestible. They pass through the digestive system relatively unchanged and help to keep the digestive system healthy.


The sum of all chemical changes that take place within an organism to maintain growth and development and convert food into energy and building blocks.


Substances in foods that are necessary for the body to function and grow. They include macronutrients, which provide energy and micronutrients, which are substances needed in small amounts such as vitamins, minerals and trace elements.

Steps to maintain a healthy weight

There are many things you can do to help keep yourself in a healthy weight range.

Monitor your weight

Regularly measuring your weight and waist circumference (at least once every three months or so) is a good way of monitoring how you are going. It means that you can make changes to your eating habits and physical activity to compensate if you have started to put on an extra kilo or two.

Eat and drink for a healthy weight

DIETARY GUIDELINES FOR AMERICANS provides guidance on how to eat a healthy diet that can help you maintain a healthy weight.

One of the keys to maintaining a healthy weight is to match your energy intake (via foods and drinks) to your energy needs. Depending on your size and how physically active you are, you may need more or less foods than other people.

Ways of doing this include:

  • Understanding the principles of healthy eating, including eating a wide range of nutritious foods each day;
  • Being aware of the energy content of various foods and beverages you consume;
  • Being aware of portion (or serve) sizes and particularly limiting your portions of high-energy foods, and;
  • Drinking plenty of water.

If you are carrying extra weight, changing your eating habits can help you with weight loss. It is important, however, to make sure that you still eat sufficient amounts of healthy food so that your body still receives the nutrients it needs.

If you are underweight, the principles of healthy eating still apply. The healthiest way to gain weight is to do it gradually, by eating a wide range of nutritious foods. You can increase portion sizes slightly and eat regularly (three meals plus snacks) every day. Gaining weight by eating large amounts of foods that are high in sugar and fat and low in nutrients is not recommended.

Dietitians can provide guidance on meal planning if you need help with planning and cooking healthy foods.

A selection of foods that can be part of a healthy diet including vegetables, fruit, meat, fish and nuts.A healthy diet will help you maintain a healthy weight. 

Be physically active

Physical activity gets you moving your major muscle groups; anything from walking and doing household chores through to running and cycling. Both your day-to-day activities, such as commuting to work or gardening, and structured activities - such as playing tennis or going to the gym - can count toward your daily activity levels.

Physical Activity Guidelines make recommendations on how much physical activity people need to do in order to enjoy health benefits.

Firstly, the guidelines recognize that any level of physical activity is better than none. If you have any medical conditions that may make physical activity unsafe, your doctor can advise what kinds of activities may be suitable for you. If you have been inactive for a while, slowly increasing your level of physical activity can help you to ease your way back into being more active.

The guidelines recommend that people carry out:

  • 150-300 minutes a week of moderately vigorous physical activity (exercise that requires effort, but is not so hard that you cannot talk, such as brisk walking);
  • 75-150 minutes of vigorous physical activity a week (exercise that requires enough effort that you are breathing hard), or;
  • A combination of moderate and vigorous physical activity.

It is more effective to spread your activity over most or all days of the week, rather than getting all your physical activity done on one or two days of the week.

Muscle-strengthening exercises are recommended to be incorporated into your routine two days a week. Although building lean muscle mass can increase your weight, it does not increase the amount of fat you carry and so does not increase your risk of health problems. It can also help to make you stronger, boost your metabolism and, over the long-term, can help you stay in a healthy weight range.

A young woman exercising.Physical activity can be a combination of moderate and vigorous exercise. 

Limit sedentary time

Sedentary time is time spent sitting. Spending more time sitting is associated with some health problems such as type 2 diabetes. It also means that your body uses less energy because major muscle groups, such as those in your legs, do not have to work as hard as when you are standing and being active.

You should limit prolonged periods of sitting by getting up frequently to break up the time you have to spend sitting.

Psychological therapies and counselling

Psychological therapies are sometimes referred to as 'talking therapies'. They may be helpful if issues such as stress, depression or anxiety are contributing to unhealthy eating habits. Psychologists or counsellors may be able to provide advice on strategies that can help you to change your behaviors and maintain your new habits.

Psychological therapies may also be helpful if an eating disorder is leading to under or overeating.

Medical conditions

A range of medical conditions can be associated with increases in weight. Examples include:

A significant and unexplained loss of weight, particularly if it persists, may be a symptom of a serious medical condition. Examples of medical conditions that can cause weight loss include:

If you are concerned regarding an unexplained change in your weight, you can see your doctor.


There are some medications that can cause weight gain in some people. These can include medications for type 2 diabetes and high blood pressure (hypertension), as well as tricyclic antidepressants and steroids.

Not all people who take these medications experience weight gain. If you are taking a medication that appears to be affecting your weight and you are concerned about it, speak to your doctor. There may be alternative medications available, your doctor may be able to adjust the dose of the medication you are on, or they may be able to give you guidance on how to limit weight gain.

Quitting smoking

People who quit smoking tend to gain weight. The amount of weight varies from person to person, but the health benefits of quitting smoking will likely outweigh any health risks caused by any weight gain. Healthy eating and regular physical activity can help to prevent or minimize your weight gain.


A feeling of tension, nervousness and dread about future events. It can trigger physical symptoms such as a rapid pulse or breathing difficulties.


Substances in foods that are necessary for the body to function and grow. They include macronutrients, which provide energy and micronutrients, which are substances needed in small amounts such as vitamins, minerals and trace elements.

Prader-Willi syndrome

A rare genetic disorder that affects development and growth, typically causing poor muscle tone, short stature, incomplete sexual development, cognitive disabilities, problem behaviors and obsessive eating.


A professional specializing in mental development, diagnoses and management of mental health conditions.

Cushing's syndrome

A group of disorders characterized by high levels of cortisol, an important chemical in the body with numerous functions including stress responses, maintaining blood sugar levels and helping the immune system.

FAQ Frequently asked questions