Exercise is a standard part of most weight loss regimens. We are reminded to be careful to keep the scales of ‘calories in and calories out’ firmly balanced in favour of calories out and exercising is our only tool for burning extra kilojoules. However, studies have shown that it is possible to reduce weight without exercising.

To understand why, it is important to understand the how kilojoules work. The average adult needs about 8700kj per day to maintain a healthy weight. But exercise accounts for a relatively small number of kilojoules expended over the course of a day. The vast majority of kilojoules expended  are used:

1. to keep our hearts beating, our lungs pumping, our synapses firing and our body’s other internal processes chugging along without any conscious intervention (this is called resting metabolic rate)

2. to digest and absorb the food we eat (thermic energy rate) and,

3. incidental energy expenditure (non-exercise activity thermogenesis (NEAT)). When you are walking to the letterbox, typing on the computer, hanging washing on the clothesline or walking to the bus stop are expending incidental energy. It is a way to account for kilojoules that are burned outside of sleeping, eating/digesting and general metabolic functions.

Where does exercise fit into this equation? Exercise is important for overall health but it is not a very efficient way to burn kilojoules. For example, a 75kg woman, walking at a 5km/h pace for 30mins will only burn around 540kj (135 calories).

Why do we get so little payoff for our efforts? A study of mice published in Current Biology vol.27 (published February 2017) showed that increases in energy expenditure through exercise were compensated for by decreases in other areas of energy expenditure. These compensatory adaptations go some way to explaining why exercise programs are often associated with only small changes in body weight. A study published in the Journal of Sports Medicine and Physical Fitness in December 2010 showed that people regularly overestimate the number of kilojoules they are expending through exercise (3 to 4 fold) and underestimate the number of kilojoules they are consuming. This helps to explain the poorer outcomes from weight reduction programs that rely on exercise alone.

So, eating a kilojoule restricted diet will lead to greater weight reduction that increasing the intensity or duration of workouts but there are a couple of important caveats.

Firstly, you need to choose the right foods to eat and the right level of kilojoule deficit. Too little won’t make the difference you are hoping for and too much will mean you are unlikely to stick with it for long enough to see a difference. The general recommendation is to aim for a 2000kj deficit each day.

Secondly, choose foods wisely. Look for foods that are nutrient dense, satisfying and that you will enjoy to eat. A few weeks ago we wrote about choosing foods for weight loss, click here to read it again.

Thirdly, there are lots of benefits to be gained by working out, and weight loss is only part of this. Exercise is important for overall health, it can lead to a reduction in cardiovascular disease, increased bone density, reduced risk of stroke, it lowers blood pressure and research shows it has a positive effect on mental health – so don’t throw away your exercise clothes just yet.

Perhaps the best way to think of it is this – weight loss is made in the kitchen, fitness is made in the gym, and optimum health combines them both.