Losing Weight

There are a lot of opinions around about weight loss, but what really works? Let's look at the evidence.

Losing Weight

Losing weight can be a challenge given that high-energy food is all around us these days, and given that there is so much conflicting information about weight loss methods. This guide discusses obesity in Australia and examines the scientific evidence regarding different approaches to weight loss. Practical advice on how to lose weight is also provided.

Obesity in Australia

According to the Australian Institute of Health and Welfare, 3 in every 5 Australians are either overweight or obese. People living in rural areas are significantly more likely to be obese than those living in urban areas.

Obesity is a major risk factor for heart disease, type 2 diabetes, some musculoskeletal conditions (such as osteoarthritis) and some cancers. Fat cells are not passive – they produce hormones and increase your risk of cancer. The image below summarises some of the complications of obesity.

Complications of Obesity

The Basics of Weight Loss

The fundamental approach to weight loss is to ensure that you burn more energy than you put into your body. That way, your body will get the extra energy it needs by breaking down fat (and in some cases muscle). That is, your energy expenditure (the amount of energy you burn) needs to be greater than your energy intake. Your energy intake is determined by what you eat and drink. Your energy expenditure is determined by your physical activity level. Even sleeping burns energy, but the more active you are then the more energy you burn.

Therefore, in theory you can lose weight by:

  • Reducing your energy intake – that is, consuming fewer calories; and/or
  • Increasing your energy expenditure – that is, increasing your physical activity.

Kilojoules, Calories, calories and Kilocalories

The term Calorie (with a leading capital letter) has a different meaning to the term calorie (all lower case). Calorie and kilocalorie (kcal) both mean the same thing. The kilojoule (kJ) is a different measure altogether. Here is how to convert between these terms:

1 kcal = 1 Calorie = 1,000 calories = 4.184 kilojoules (kJ)

Here are some examples of how to convert between kilocalories and kilojoules:

1 kilocalorie (kcal) = 4.184 kilojoules (kJ)

Therefore, if you know a food item has, say, 1,431 kJ then you can calculate the kilocalories:

1,431 kJ = 1,431/4.184 = 342 kcal

Conversely, if you know an item of food has 250 kcal, then you can calculate the kilojoules:

250 kcal = 250 x 4.184 = 1046 kJ

Losing Weight: The Scientific Facts

Much research has been conducted to figure out how people can lose weight successfully. Here are the most important conclusions of that research:

  • Despite the energy balance explained above, research has shown that getting more exercise is not likely to be an effective method of losing weight (e.g. Amorim Adegboye & Linne, 2013). Exercise is nevertheless very important for your cardiovascular health – please don’t miss the Exercise For Everyone article.
  • Popular diet programs like Atkins diet, Weight Watchers, Zone and Ornish diets produce similar results after six months (Truby et al, 2006; Dansinger et al, 2005). The key is just to ensure that your energy intake is less than your energy expenditure.
  • Some popular diet programs (such as Ornish, Weight Watchers high-carbohydrate, and New Glucose Revolution weight-loss plans) have better dietary quality than some popular low-carb/high-protein diets and should therefore be more likely to prevent cardiovascular disease (Ma et al, 2007).
  • There is no need to starve. One study that compared two groups. One group had an intake of 400 kcal per day and the other group had an intake of 800 kcal per day. There was no difference in weight loss outcomes for the two groups (see Bray, 2013).

Are You Overweight or Obese?

There are two commonly used methods to determine whether your weight is in an unhealthy range: body mass index (BMI) and waist circumference. BMI is a very common method, but waist circumference is actually a better predictor of your risk of developing chronic disease.

Body Mass Index (BMI)

To find out whether you are obese or overweight, please use the BMI Calculator. The BMI Calculator will also display your BMI and, if you are outside the normal weight range, it will display your recommended weight range.

The chart below can also be used to determine the recommended weight ranges for your height.

Healthy Weight Chart
Source: Australian Health and Medical Research Council 2013, Australian Dietary Guidelines with no modifications.

Waist Circumference

To measure your waist circumference:

  1. Measure against your bare skin;
  2. Breathe out normally;
  3. Find the point on the side of your waist that is half way between the bottom of your ribs and the top of your hip bone (pelvis) then fit the tape around your waist at this height. Don’t pull it tight – just fit it so that it sits on top of your skin; and
  4. Read the measurement.

Are you at increased risk of chronic disease? Check the table below:

Waist circumference risk

How To Lose Weight

1. The Mathematics of Weight Loss

If you are not keen to know the mathematical details, then skip this section of this page and jump straight to this US Government calculator to see how many Calories you need to consume each day to reach your target weight, and how long it will take you to get there:

USDA Calorie Target Calculator

Remember, to convert from Calories to kilojoules just multiply by 4.184.

Here is a little more detail for those interested…

To stay at the same weight, you need to eat approximately 100 kilojoules (24 kilocalories) per kilogram of body weight per day. For example, if you weigh 80 kg then you need to consume:

Kilojoules to maintain body weight for an 80 kg person = 80(kg) x 100 kJ = 8,000 kJ per day

If you consume fewer kilojoules than the number you need to maintain your body weight, then you will lose weight. In our example, an 80 kg person should lose weight if he/she consumes less than 8,000 kJ per day. You may need more energy than this depending on how active you are.

For a more personalised estimate of how many kilocalories (Calories) you need each day to maintain your body weight, please see the Adult Energy Needs and BMI Calculator from the United States Department of Agriculture (USDA). The USDA calculator will tell you the number of Calories you need each day. To convert to kilojoules, multiply that number by 4.184. For a collection of other useful dietary calculators and counters from the USDA, please click here.

So, by now you have hopefully calculated how many kilojoules (or kilocalories) you need to consume each day to maintain your current weight.

To lose 1 kg of weight, you need to forego about 32,000 kJ (7,650 kcal) of energy. Therefore, if you reduce your daily energy intake so that it is, say, 2000 kJ (480 kcal) less than the amount you need to maintain your body weight (as described immediately above) then you will take 16 days to lose one kilogram (since 16 days x 2,000 kJ = 32,000 kJ).

2. Weight Loss Strategy

Here are some tips about choosing your weight loss strategy:

  • Choose a diet that suits your food preferences as much as possible, but don’t leave out any major food group.
  • Be realistic with your expectations. It is a long-term process and what is required is a long-term change to your lifestyle. How much you can lose depends on how overweight you currently are. As a general guide, aim to lose 0.5-1 kg per week.
  • Don’t lose weight too quickly – it can be dangerous. During rapid weight loss you may burn significant amounts of muscle. When muscle breaks down, the contents of your muscle cells spill into your system are toxic to your kidneys.
  • Please consult your doctor first, especially if you are considering cutting your intake to less than 1200 kcal (5000 kJ) per day.
3. Exercise

Exercise reduces your risk of chronic disease and studies have found that people who exercise as part of their weight loss strategy are more likely to keep the weight off. So for long-term health and to maximise your chances of success with your weight loss program, get at least 30 minutes of exercise on at least five days per week. For more information on the benefits of exercise, please see Exercise For Everyone.

4. Medication

There is no magic medicine to reduce your weight, but there are some medications that can help in some cases. If your BMI is over 30 kg/m2 and you have not been able to reduce your weight with diet and exercise alone, then speak to your doctor about medication options.

5. Modify Your Behaviour

If you have trouble persevering with your weight loss program, ask your doctor about getting assistance from a psychologist. Strategies used by psychologists may include: use of food diaries and activity records; managing the stimuli that trigger you to eat; learning to eat more slowly; meal planning; getting social support and learning strategies to help you persevere. You may also find self-help/motivation books useful.

6. Surgery

If you have been unable to lose weight and have a BMI of over 40 kg/m2 then bariatric surgery may be an option for you. Bariatric surgery refers to a range of surgical procedures that are intended to produce weight loss, such as placing a band around your stomach. Bariatric surgery can be a very effective treatment for some people, but there are risks too. Please consult your doctor for further advice.

7. Complementary Medicines

There is limited research on the safety and effectiveness of many complementary medicines for weight loss. However, studies have shown that chitosan, guar gum and green tea are ineffective. Furthermore, some herbal medicines are downright unsafe.

How To Keep The Weight Off

There are some similarities among the people who are able to keep the weight off following their weight loss program. You can follow in their footsteps if you take at least some of these steps:

  • Get regular exercise;
  • Lose at least 2 kg every 4 weeks until you reach your target weight;
  • Attend a weight loss program or support group;
  • Believe that you can control your weight (after all, you can!); and
  • Modify your eating behaviour – if necessary, ask your doctor about getting help from a psychologist so that you can take control.

Good luck. You can do it!


  • Amorim Adegboye AR, Linne YM. Diet or exercise, or both, for weight reduction in women after childbirth. Cochrane Database of Systematic Reviews 2013, Issue 7. Art. No.: CD005627. DOI: 10.1002/14651858.CD005627.pub3.
  • Australian Government 2010, Measure Up, accessed 15 Feb 2014.
  • Australian Institute of Health and Welfare 2013, Overweight and obesity, accessed 15 Feb 2014.
  • Bray, G 2013, Patient information: Weight loss treatments (The Basics), UpToDate, accessed 15 Feb 2014.
  • Centers for Disease Control and Prevention (CDC) 2011, “Losing Weight: What Is Healthy Weight Loss?”, http://www.cdc.gov/healthyweight/losing_weight/index.html, US Government, accessed 25 Feb 2014.
  • Dansinger ML, Gleason JA, Griffith JL, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA 2005;293:43–53.
  • Ma Y, Pagoto SL, Griffith JA, Merriam PA, Ockene IS, Hafner AR, Olendzki BC. A dietary quality comparison of popular weight-loss plans. J Am Diet Assoc. 2007;107:1786–1791. doi: 10.1016/j.jada.2007.07.013.
  • Truby H, Baic S, deLooy A, et al. Randomised controlled trial of four commercial weight loss programmes in the UK: initial findings from the BBC diet trials. BMJ. 2006;332:1309–14. doi: 10.1136/bmj.38833.411204.80.
  • UpToDate 2014, Overview of Therapy for Obesity in Adults, accessed 15 Feb 2014.