How many kilojoules should I burn a day for weight loss?

Your body needs a certain amount of energy to perform all its normal functions, like breathing and blood circulation, and to help sustain itself throughout the day.

Kilojoules (kJ) are a metric used to measure the amount of energy we get from different kinds of foods and drinks and the amount of energy we expend each day.

The number of kilojoules needed to maintain a healthy weight often depends on things like your age, height, weight and even your lifestyle. For example, it will be different if you're predominantly standing at work, versus if you're an office worker sitting 8+ hours a day.

To help you get started, we're doing a deep dive into all things weight loss and kilojoules, including what factors influence the number of kilojoules you should be burning each day and how many kilojoules you should be burning to achieve healthy and sustainable weight loss.

What are kilojoules?

If you've ever had a look at the labels on the back of your favourite items, you will see a long list of information about those foods or drinks, including the kilojoules contained in each item.

In Australia, we use kilojoules to measure how much energy you consume from foods and drinks. Different foods and drinks contain a different number of kilojoules depending on the ingredients and the serving size [1].

Your body requires energy to perform its daily functions, like keeping you going throughout the day and getting you moving. If your kilojoule intake is greater than what your body uses, this extra energy can be stored as fat [1].

On the other hand, if your kilojoule intake is less than what your body uses for energy, you'll be more likely to lose fat [1].

What is the daily energy requirement for adults?

Your daily energy requirements will look a little different depending on whether your body needs more energy or less energy. But, for the average adult to maintain a healthy weight, their body needs 8,700 kilojoules per day [1].

What factors influence your kilojoule requirements?

Some people will need to consume fewer kilojoules, while others need to consume more. For example, someone who engages in strenuous activity will need more energy to keep them going throughout the day than someone with a more sedentary lifestyle.

Let's take a closer look at the many factors that influence your daily energy requirements.

Physical activity

The amount of exercise you do each day influences the amount of energy your body needs. Someone who is lightly active won't need to consume as many kilojoules as someone who exercises strenuously.

Body composition

The greater muscle mass you have, the more energy your body needs and the more kilojoules you need to sustain your day. Generally speaking, as you get older, the less muscle mass you have, which will impact your kJ intake.

Body composition also varies between men and women. Men generally have greater muscle mass than women, so more kilojoules are required to maintain energy throughout the day.

Life stage

Other factors, like pregnancy, influence kilojoule requirements. Pregnant women typically need an additional 1400 kJ per day in the second trimester and 1900 kJ extra in the third trimester [1].

Weight loss

If you're trying to lose weight, you need to be consuming fewer kilojoules than what your body is burning. For example, to lose half a kilogram, you need to consume roughly 2000 kJ less than your body uses for energy [2].

How do you calculate how many kilojoules you need per day?

As we know by now, the amount of kilojoules your body needs each day depends on a variety of factors. Hence, it's important to get personalised advice from a health professional like your GP or an accredited practising dietitian.

But, there are a bunch of online calculators from trusted sources that can be used as just a starting point to help you figure out approximately the amount of kilojoules your body needs.

The Australian Government's Eat for Health calculator provides estimates for your daily energy requirements based on your gender, age, weight and exercise levels [3].

• Maintain weight: If you want to maintain your current weight, you enter your actual body weight in the calculator
• Lose weight: If you're looking to lose weight, you enter your ideal body weight in the calculator, which will give you a lower estimated energy requirement that can be used as a starting point for weight loss

How do I know how many kilojoules are in food and drink?

Sometimes it can be tricky to work out approximately how many kilojoules are contained in the foods we eat, particularly when we're using a bunch of different ingredients to make food at home or when eating out.

If you're at the grocery store you can work out how many kilojoules are in specific foods by reading the nutrition label on the back of packaged foods [4].

If you're eating out at a cafe or restaurant, it can be harder to check as most places don't list the nutritional value of their meals. But, as a general guide, you can figure out which types of foods have greater or fewer kilojoules [4]:

• High-fat and high-sugar foods and alcohol contain the most amount of kilojoules
• Protein and carbohydrates contain a modest amount of kilojoules
• Fruits, vegetables, legumes and dietary fibre contain lower amounts of kilojoules

How many kilojoules should I burn a day?

There's no definitive answer for the number of kilojoules you should be burning each day because it largely depends on your goals — like if you're trying to maintain, lose or gain weight — and is even influenced by your age, sex, and muscle mass.

The average adult who simply wants to maintain their weight needs 8,700 kJ to sustain themselves throughout the day, so you should strive to burn a little more energy than what you're consuming.

For the average adult, Australia's Physical Activity Guidelines recommends getting at least 30 minutes of exercise each day to keep your body moving and burning energy. This includes [5]:

• 2.5-5 hours a week of moderately intense exercise like a walk or going for a swim
• 1.25-2.5 hours a week of strenuous physical activity like running, playing a team sport or a gym session

The amount of energy you burn from exercise also depends on your weight, age and the type of exercise you're doing. You can use a bunch of different online calculators to get an estimate of the number of kilojoules you can expect to burn based on your workout habits.

How many kilojoules do I need to burn to lose weight?

The key to losing weight is to strike a healthy balance between energy in and energy out. That means you need to be burning more than you're consuming.

There are no specific answers for how many kilojoules you need to burn each day for weight loss, as this may vary depending on how fast you want to lose weight and your activity levels.

To lose half a kilogram of fat, you need to either burn 2000 kJ or eat 2000 kJ less per day, which can make a big difference in your weight loss journey [2].

2000 kJ can be quite daunting, but making small and sustainable changes to achieve your weight goal (like decreasing your energy intake by 100 kJ a day) can be a great starting point [2].

It's important to remember that everyone's weight loss journey is different. It's always best to consult your health professional to get personalised advice that works for you.

How to approach weight loss

Although weight loss can look different for everyone, there are plenty of simple things you can do to kickstart your journey to a healthy weight.

Lifestyle changes

Weight loss can be daunting and overwhelming for many people. But, achieving your ideal body weight within a healthy period of time can happen by making small, incremental lifestyle changes like following a balanced diet and improving your exercise levels.

You can achieve this by finding an exercise routine that you enjoy doing and practising it consistently. You don't have to exercise strenuously every single day but moving your body daily can make a big difference whether that's going for a walk, swimming, hitting the gym or taking a Pilates class.

Plus, eating a balanced diet by incorporating foods from each of the 5 dietary groups can also help you achieve your goals [6].

Eating lean proteins, fibre-rich foods and whole grains, and vegetables can help keep you fuller for longer and curb your hunger so you're not exceeding your daily energy requirements, but also not starving yourself.

Science-backed meal replacement shakes

Weight loss shakes are essentially liquid meal replacement drinks that you can use in combination with a weight loss program to replace one or more meals out of your day. But, not all meal replacement shakes are created equal, with some lacking the right nutritional value.

That's why Juniper's Nourish Shakes are dietitian-approved to support lasting weight loss while having all the nutritional benefits of a balanced meal.

Each shake is packed with 20 vitamins and minerals, and nearly 30g of high-quality protein (and no bad stuff like added sugar, laxatives, preservatives or empty fillers). These shakes can be a powerful way to kick-start your weight loss journey while nourishing your body with everything it needs to stay fit and healthy.

Holistic weight loss program

Understanding the right number of kilojoules you should be consuming and burning each day can be tricky to wrap your head around, particularly at the start of your weight loss journey. Juniper's Weight Reset Program can help you make sustainable lifestyle and habit changes backed with personalised health coaching so you can reach your weight goals.

Get treatment that targets weight gain on a biological level, plus a dietitian-led program that supports long-term weight maintenance.

It also includes one-on-one health tracking and weekly check-ins with your health practitioner to track your biometric, mental and physical health, continuously making adjustments to your program to suit your individual needs.

Ultimately, the number of kilojoules you should be burning a day to kick your weight loss goals depends on a bunch of different factors. But, for the average adult maintaining a healthy weight starts with striking a balance between the amount of energy you're putting out with the amount of energy you're putting in.

Image credit: Getty Images