A fundamental principle of nutrition and metabolism is body-weight change associated with energy balance. Energy balance, summarised as ‘Calories In vs Calories Out’ dictates body mass gain, loss and maintenance, and is crucial when formulating your weight goals.
Calories Out – estimated as 2500 kcals per day for menand 2000 kcals per day for women is determined by:
- Basal Metabolic Rate (BMR) 60-70%. This is the number of calories your body uses at rest for processes such as thermoregulation and immune function. The number one determinant of this is muscle mass, which is 10 times more effective to BMR than fat mass
- Thermic Effect of Feeding (TEF) 5-10%. This can be marginally increased through a higher protein diet
- Non-Exercise Activity Thermogenesis (NEAT). This is activity that isn’t a structured form of exercise, such as standing, steps, cooking and cleaning. For example, standing needs twice as much energy as sitting, and doing 10,000 steps uses approximately 300-500 kcals
- Structured Exercise in the form of resistance or cardiovascular exercise. Although this will use calories, the outcome of these sessions should be focussed around optimising muscular and cardiorespiratory performance, rather than using the most calories possible. Think of burning calories as a bonus
Calories In – determined by what we eat and drink. Foods that provide energy are called macronutrients with certain types being more calorie dense than others:
- Protein – 4 kcals per g – has the benefit of being the most filling of macronutrients
- Carbohydrate – 4 kcals per g – same energy density as protein – fibrous sources are the most filling
- Fat – 9 kcals per g – very energy dense and therefore recommended portion size is lower
- Alcohol – 7 kcals per g – often seen as ‘empty’ calories as the body can’t use them for fuel or energy
It is exceptionally difficult to accurately measure both Calories In and Calories Out and therefore the best way to know if you’re in a surplus or deficit is to monitor your weight over time. If it is consistent over a fortnightly period, then you’re in calorie balance.
To lose 1kg of body fat you must be in a 7,000 kcal deficit. In the fictitious graph above energy balance is 2500 kcals. Over the course of the week this individual has created a total deficit of 3,500 kcals and as such would have lost approximately 0.5kg of fat (please note this is an estimation not an exact science).