How to Reduce Energy Intake

Reducing energy intake via dietary change is the primary component of a weight loss intervention. Diets aiming to reduce energy intake can be divided into three categories defined by the total amount of calories consumed per day (see table below).

Some health professionals may have the skills and expertise to support patients using hypocaloric/reduced energy diets. Further specialised training would be required to prescribe and supervise more restrictive diets.

*It is useful to understand the terms ‘calories or kilocalories (Cal/ kCal)’ and ‘kilojoules (kJ)’. Both represent the amount of energy we get from food and drink on different scales, with kilojoules being the metric measure. There are roughly 4 kJ to each kCal.

These diets work by creating a scenario in which the calories consumed are less than the calories burned. To put this another way, more energy is expended than the equivalent caloric intake.

Daily Energy Expenditure

There are three main contributors to total daily energy expenditure:

• Basal metabolic rate or resting energy expenditure – This is the largest source accounting for around 60-80% of energy expenditure.¹ It includes energy required to keep the body functioning and in homeostasis at rest such as regulating and maintaining breathing, body temperature, blood circulation, central nervous system function, cell growth etc. It is different for different people – typically higher in males than females, in younger versus older people and in heavier versus lighter people.
• Physical activity and exercise – Another 10-20% of daily energy expended comes from this source depending on activity levels.
• Thermic effect of food (TEF) – This refers to the energy which is used in processing and storing of consumed food and accounts for approximately 10% of the total daily energy expenditure. This amount varies for different food groups – for example, the TEF is greater for protein than it is for fat so the energy expended processing protein is greater than that processing fat.

Creating an energy deficit is essential for weight loss. Since the greatest proportion of energy expenditure comes from our basal metabolic rate with a much smaller proportion coming from physical activity/exercise, it makes sense that for those aiming to achieve weight loss, reducing caloric intake through diet should be the primary focus, with exercise the secondary focus. It may be helpful to remind those attempting weight loss or weight management how much exercise they would actually need to do to burn off the calories from different types of foods: For example, loosely based on someone weighing 69 kg:

• Jam donut – walk for 40 mins
• Big Mac – walk 9.6 km
• Small popcorn and butter – elliptical machine for 135 mins

It is much easier to forego extra snacks than it is to burn them off!