Understanding optimal kilojoule intake for effective weight loss

Find out what role our kilojoule intake and the 'starvation mode' has on our weight loss efforts.
Published 9 July 2017 | Updated 6 June 2024

In order to lose weight an individual needs to consume less energy (kilojoules/calories) than the body will 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 500 grams per week weight loss. Understanding this relationship between energy intake and expenditure is key to successful and sustainable weight management.

Determining your daily kilojoule requirement

Understanding your body's daily energy needs is essential for achieving and maintaining a healthy weight. On average, an adult requires around 8,700 kilojoules (kJ) per day to sustain their current weight, which is roughly equivalent to 2,080 calories. However, it's important to note that this figure serves as a general guideline and can vary significantly based on individual factors such as age, sex, height, weight and activity level. These variables play a pivotal role in determining the precise amount of energy our bodies require to function optimally.

Impact of metabolism on weight loss

Restricting kilojoule intake can lead to a slowdown in metabolism. As you decrease your kilojoule consumption, your metabolism naturally adjusts, becoming more efficient as your body adapts to the reduced energy supply. Consequently, this can slow (but not stop) the anticipated rate of weight loss.

For instance, if an individual's maintenance kilojoule requirement is 8,700 per day, reducing intake to 6,600 kilojoules while maintaining the same level of exercise should result in a weekly weight loss of approximately 500 grams. Similarly, further reductions to 4,500 kilojoules and 2,400 kilojoules per day could yield weight losses of 1 kilogram and 1.5 kilograms per week, respectively.

However, when intake is drastically reduced to 2,100 kilojoules per day, the expected weight loss of 1.5 kilograms per week may not be sustained due to the decreased metabolic rate. Instead, weight loss may plateau around 1 kilogram per week. This difference in weight loss rate underscores the distinction between slower-than-expected weight loss and the concept of "starvation mode," which suggests no weight loss occurs despite reduced intake.

However, it's important to acknowledge another crucial aspect influencing weight management: the body's 'set-point.' This is the weight range in which your body naturally tends to settle, influenced by genetic and environmental factors. Understanding your set-point weight can provide valuable insights into your weight loss journey.

What is the starvation and weight loss myth?

The ‘starvation mode’ theory is when a person trying to lose weight reduces their kilojoule intake enough that they actually slow down their metabolism, which prevents further weight loss from happening. While the concept of 'starvation mode' may seem logical, there is little scientific evidence to support it.

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. Studies show over-restricting food or depriving ourselves from food actually makes us more likely to overeat these foods. The reason for this is that we may experience triggers for certain foods 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, it is a good idea to 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 we 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 be experiencing this 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 reached 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.

Benefits of a gradual approach to sustainable weight loss

Both the Australian Dietary Guidelines and WeightWatchers® suggest a safe rate of weight loss is between 500 grams and 1 kilogram per week. You may lose more in the first few weeks, but this should even out over time. Losing weight too quickly isn’t good for your health, and can actually make it harder for you to sustain the weight loss long term. Losing weight too quickly can also pose a risk to your overall health including developing gallstones, irregular heartbeat and excessive loss of lean muscle mass. Following a ‘quick-fix’ approach to weight loss also doesn’t help you work on the root cause of your weight gain in the first place.

Weight loss isn’t just about what you eat and the activity you do – it’s about your mindset and the way you think as well. Shifting your mindset takes time, that’s why a slow and steady approach will turn out to be the most effective in the long run.