We each have a daily kilojoule ‘budget’ that can be estimated based on our age, weight, height and our general activity level. This budget can be increased if you want to gain weight, or decreased if your aim is to lose weight.
Working out your kilojoule budget
Even at rest, your body burns energy (kilojoules/calories) as it fights infection, keeps your organs functioning, keeps your body temperature stable, and breaks down, recycles and rebuilds hormones, enzymes, cells and other essential components of body systems. This energy requirement for essential body functioning is called Basal Metabolic Rate (BMR) and is calculated based on your weight, height, and age. (If overweight, the best estimate of BMR is calculated using an ideal weight for height, rather than actual weight).
Once you start moving, your metabolism increases as you need extra kilojoules to fuel your muscle activity. That means your Estimated Energy Requirement is a combination of your BMR and your average activity level. This is only a guide as each body is different and activity levels can vary significantly from day to day.
If you keep to your budget, and the kilojoules you consume balance the kilojoules your body burns each day, then your weight will stay the same. If you consume excess kilojoules, this energy is stored as excess body weight. And if you under-consume kilojoules, your body uses up your body energy stores, resulting in weight loss.
When your goal is to lose weight, reducing your daily kilojoule intake by around 2100 kJ each day will help you slowly but surely achieve a healthy weight.
Spending your kilojoule budget
Once you have calculated your kilojoule budget, you can focus on the quality and quantity of food and drinks you choose. Ideally, the majority of your kilojoules should be spent on food essentials – the whole foods, rich with nutrients needed by our bodies for good health. Any of the leftover budget can be spent on small amounts of low nutrient foods and drinks – the treats, the empty calorie choices, takeaway and indulgence foods.