How Many Kilojoules Should I Eat To Lose Weight


How Many Kilojoules Should I Eat To Lose Weight? The amount of kilojoules you need each day depends on your current weight, height, gender and age. You should be able to consume all the kilojoules you need from the number calories you eat and drink. If you’re trying to lose weight, you’ll likely be counting the number of kilojoules you eat. In fact, many dieters say they successfully lose weight when counting kilojoules, but is this true?

Energy (kilojoules)

A kilojoule (kJ) is simply a measure of energy. For our bodies to function, we need energy to fuel them. Under Australian food laws, it is a requirement to display energy as kilojoules to describe the amount of energy found in a serve of food. Another term you might have heard of for energy is calories. Calories are an American measure and will often be seen on American packaged goods. These terms are used interchangeably to talk about energy. However, it is important to know that 1 Cal = 4.2 kJ.

How many kilojoules does a person need?

The average daily kilojoule (energy) requirement for an adult is approximately 8700kJ or 2000Cal. A person’s daily energy requirements differ based on their gender, how much exercise they do, their height and weight, and whether or not they suffer from particular illnesses or disorder. While the average healthy Australian adult requires about 8700kJ/day, this may differ for you and will undoubtedly differ for your child.

What is excess energy? 

When it is said that food contains excess energy, it means that it could lead to eating more kilojoules than your body requires. When excess energy is consumed (above our daily energy needs) it gets stored as fat. This could increase the risk of becoming overweight or obese if not balanced with exercise.

The food we eat contains varying amounts of energy depending on how much fat, carbohydrates, protein or alcohol it contains. Each gram of fat provides 37kJ in comparison to carbohydrates and proteins, which contain 16kJ and 17kJ respectively. Alcohol contains 27kJ/g.

This is why there are warnings around consuming a high-fat diet, as it’s the most energy dense nutrient. Eating too much fat could quickly lead to excessive kilojoule (energy) intake and consequent weight gain. However, it’s important to remember that not all fats, carbohydrates or proteins are nutritionally equal.

How Many Kilojoules Should I Eat Per Day?

In order to achieve weight loss an individual needs to consume less energy (kilojoules) than the will body burn. For example if an individual needs 8,700 kilojoules per day to maintain weight, reducing daily intake to 6,600 kilojoules (assuming exercise stays the same), should provide around 500g per week weight loss.

The average adult needs about 8,700 kilojoules (kJ) a day to maintain a healthy weight. This number is a average and varies based on many factors including how active we are, our age, sex, height and weight. Our body then uses this energy to keep our body functioning.

Starvation and weight loss

Your metabolism can slow down during kilojoule restriction. It’s true, as you start to restrict your kilojoule intake, your metabolism will reduce. As your body starts to lose weight it becomes more efficient, requiring fewer kilojoules to perform the necessary daily functions for survival. Consequently, this can slow (but not stop) the anticipated rate of weight loss.

For example, if an individual needs 8,700 kilojoules per day to maintain weight, reducing intake to 6,600 kilojoules, assuming exercise stays the same, should provide a 500g per week weight loss (note: 500g of weight is equivalent to about 14,700 kilojoules). Furthermore, reducing to 4,500 kilojoules should result in a weight loss of 1kg per week and going down to 2,400 kilojoules a day should result in a weight loss of 1.5kg per week. However, if an individual actually reduces their intake to 2,100 kilojoules, the weight loss would not likely be a steady 1.5kg per week because of the reduced metabolic rate. It would likely be around 1kg. This ‘lower than expected’ rate of weight loss is a lot different to ‘no’ weight loss as the ‘starvation mode’ notion proposes.

What is the starvation myth?

The ‘starvation mode’ theory is when a person trying to lose weight reduces their kilojoules intake enough they actually slow down their metabolism, which prevent further weight loss from happening.

Does starvation work for weight loss?

While there is no ‘biological’ evidence to support the ‘starvation mode’ myth, there may be behavioural reasons why weight loss stops when kilojoules are severely reduced. Science shows over-restricting food or depriving ourselves from food actually makes us more likely to overeat these foods. The reason for this is that we experience cravings for the food and when the opportunity eventually arises to eat this food, we haven’t created a plan for how to eat it in moderation. Instead of heavily restricting the foods you eat, learn how to incorporate them into your diet in a healthier way.

Another common reason for a weight plateau is being less diligent with your eating and activity behaviours. Often when we start a weight loss program we’re highly motivated, following the program religiously, tracking everything we eat and moving more each day. But as the weeks or months go by our motivation can start to waiver and old unhealthy habits can start to slip back into our routine. We often avoid keeping ourselves accountable when this happens, and sometimes we don’t even realise our portion sizes have crept up or we’re reaching for a second serving. If you think you may have fallen into this trap, the best thing is to go back to basics and start following the program like you were when you first started.

The good news is once you’ve achieved your weight loss goals and your weight has stabilised, it does not appear that the dip in metabolism is permanent. Several studies showed that metabolism goes back to expected levels with sustained weight loss, discounting the theory that a lowered metabolism helps to explain the common phenomenon of weight regain following weight loss.

How Many Kilojoules Do I Consume To Lose Weight?

Although each person is different and your ideal kilojoule intake depends on your height, weight and muscle mass, I can give you a rough guide of how many kilojoules you should be consuming to lose weight.

The key to losing weight is to eat less kilojoules than you are using with activity and your natural metabolic rate, so your body uses its fat stores.  But you need to eat more than youre minimal metabolic rate otherwise you start to breakdown muscles for energy, making it hard for you to maintain weight loss in the long term.

Basic guide:

1) Each meal – about 1500 kilojoules per meal
2) Snacks – 500 kilojoules per snack, 2 a day

Total – 5500 kilojoules per day

How Many Kilojoules Should You Consume Per Day For Weight Loss?

FOR years weight management has been about counting calories. But is taking a mathematical approach to weight loss the best answer?

With a plethora of calorie-tracking apps, nutritional information on food labels, and now menu boards and price tags with calorie counts, it’s hard not to be at least calorie-conscious.

Calories and kilojoules are common language*. With kilojoules (kJ) being the Australian preference, a kilojoule is a measure of how much energy people get from consuming a food or drink.

We get that in order to stay the same weight, we need to eat roughly the same amount of kilojoules as we burn. For the ‘average’ adult this is about 8700 kilojoules (roughly 2000 calories), if the surveys are correct. This magic number is widely used as an approximate figure for achieving and maintaining a healthy weight and as the basis of food labels and fast food menu boards.


Whether it’s an apple, a chocolate bar or a bowl of soup — a kilojoule is still a kilojoule, right? At least, that’s what dieters have been told for the past half-century. The problem is, not all kilojoules are created equal.

If you compare a plain croissant with jam and large full-fat latte to a small bowl of untoasted oat-based muesli with low-fat milk, fresh berries, and a dollop of yoghurt, served with two slices of toast with peanut butter, finished off with a cup of tea, it’s hard to believe that they are equal in kilojoules — roughly 2500 kJ (600 cal) for both meals.

Peanut butter toast is just the desert for the first option, and yet it still looks more filling than a croissant. Picture: Mitch Cameron.

Peanut butter toast is just the desert for the first option, and yet it still looks more filling than a croissant. Picture: Mitch Cameron.

Clearly this doesn’t appear right, especially given that scoffing a croissant and coffee (most likely on the run) will not give you that same full feeling as sitting down to a bowl of breakfast cereal, toast and fruit.

Different foods have varying affects on satiety (how full you feel after eating). In other words, your body responds differently to calories from different sources.


Let’s take a closer look at why the quality of kilojoules determines the quantity your body burns or stores. You’ll get so much more fibre in muesli, toast and fruit than in a croissant (13 grams versus 2 grams) and very few of the kilojoules would actually get absorbed because somewhere along the line your gut bacteria have burned them for their own energy source. Those that did would get absorbed very slowly causing your stomach to distend, sending signals to your brain that you were full.

As for carbohydrates, you may think that a bowl of cereal with toast and fruit is ‘carb heavy’ but it’s the types of carbs that matter most. The type of carb found in croissant and jam tend to have a higher gylcemic index (GI) meaning there’d be a high sugar spike. This would start a domino effect of high insulin and a cascade of hormonal responses that wreaks havoc on metabolism.

This breakfast might be high in calories, but it’s low in long-term satisfaction.

This breakfast might be high in calories, but it’s low in long-term satisfaction.

The high insulin increases storage of belly fat, increases inflammation, raises triglycerides and LDL (bad) cholesterol.

Likewise with fat. Studies have shown that around 20 per cent of the fat in nuts (in this case the peanut butter on toast) is not absorbed by the body. The fat in nuts is trapped in fibrous cells, which stops our bodies from absorbing the fat, excreting it instead.

Protein is another vital nutrient that will help you feel full by stimulating a release of hunger hormones that signal the brain you’re full. FYI: There’s almost twice as much protein in the muesli meal compared to a croissant and coffee.


This is not to say that crunching the numbers is an archaic task — it does have some merit. It can provide structure, and sometimes personal tracking is what some people need to become more aware of habits and encourage behavioural change.

Secondly, it’s most certainly easier to get out the calculator than actually understanding the complex effects food has on our bodies (as noted above).

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