Dietary guidelines broadly recommend a daily intake of 10,000 kilojoules (2,400 calories) for men and 8,000 kilojoules (1,900 calories) for women.
But what do these figures mean in the context of the number of kilojoules or calories you personally need to maintain a healthy body weight?
I’m going to stick with kilojoules in this article because kilojoules – not calories – are the metric unit for measuring energy, just as kilograms – not pounds – are the metric unit for measuring body weight.
Daily kilojoule requirements are based on many variables, and no two people are the same across all of these parameters.
It makes sense then that if we all followed the same prescriptions for kilojoule intake, some of us would gain weight while others might lose some.
That’s because any excess or deficit between the number of kilojoules you consume and the number your body uses results in weight gain or loss.
So how can you know what you need to maintain your energy balance? There are two options: the mathematical approach, which requires kilojoule counting, and the instinctive approach, which involves “listening” to your body (my personal preference).
Both approaches take some trial and error.
The mathematical approach
One way to estimate how many kilojoules you need is to use an online calculator that takes into account major factors regulating energy requirements. These include your sex, weight, age and activity levels. Some calculators also take height into account.
Such calculators are based on prediction equations that estimate true energy requirements – as measured in a laboratory – from readily available parameters.
While some prediction equations may be slightly better than others, none of them can tell you exactly how many kilojoules you need to consume to maintain your weight. That’s because no prediction equation can take your genetic make-up, which may impact how fast or slow you churn through kilojoules, into account.
Nor can they account for things like whether you have more or less lean mass or fat on your body than the average adult. Or that you may have spent the last few months on a weight-reducing diet that has dropped the amount of energy you need to maintain your weight by a few thousand kilojoules per day.
Despite these limitations, once you have a ballpark figure of your energy requirements, you can roughly work out how much you need to eat and drink based on the kilojoule content of the foods and beverages you consume.
For this you will need a comprehensive kilojoule counter (I recommend CalorieKing, which has extensive data bases for Australia and the United States) and a way to track your food and beverage intake throughout the day (MyFitnessPal comes highly recommended). Numerous other programs and apps are available for both.
The instinctive approach
We also have the ability to maintain a healthy body weight without any regard for kilojoule counting; the human body is endowed with a remarkable system that enables us to attain and maintain an optimum weight instinctively.