How Many Calories Should I Have?

You've probably been wondering or have wondered at some point in your life, just how many calories should I consume each day. In this article I set out one way of calculating your intake requirements - though please bear in mind that all formulas are a guideline which you need to use as a starting point depending on what is happening in your body and what your goals are.

Please also remember that calories are not created equally, you must still consider keeping your ratio of Carbs:Protein:Fat, also avoid too much saturated fats and simple sugars (except within the magic 30 minute window after training hard).

Factor affecting energy requirements

The following factors will have an influence on an individual’s energy requirements.

  • Activity levels
  • Exercise
  • Occupation
  • Lifestyle
  • Age
  • Gender
  • Body mass
  • Body composition
  • Environment temperature
  • Diet
  • BMR (basic Metabolic Rate)
  • Basic Metabolic Rate (BMR)

BMR is an individual’s basic requirement of energy at rest. This energy will be adequate to maintain the body’s basic function without any movement. One of the main influences of BMR is body composition. Even at rest muscle cells are metabolically more active than fat cells.

Calculating BMR

One of the most commonly used methods of calculation is the Schofield calculation. This calculation uses the variables of gender, age, height and weight to calculate an individual’s BMR. A factor is then applied based on their activity levels. This factor may be described as PAL- Physical Activity Level.

Calculation that factor in lean body mass will be more accurate when calculating BMR, as lean tissue is more metabolically active than fat tissue.

The Schofield Calculation

Men:

10 - 17 years     BMR = 17.7 x W + 657    SEE = 105

18 - 29 years     BMR = 15.1 x W + 692    SEE = 156

30 - 59 years     BMR = 11.5 x W + 873    SEE = 167

 

Women:

10 - 17 years     BMR = 13.4 x W + 692    SEE = 112

18 - 29 years     BMR = 14.8 x W + 487    SEE = 120

30 - 59 years     BMR =   8.3 x W + 846    SEE = 112

 

Key:

W = body weight in kilograms

SEE = standard error of estimation

The SEE value means the calculated BMR could be this number of calories out, in other words either too many or too little.

In addition to calculating BMR we have to add a factor which will account for an individual’s physical activity level (PAL)

So:

BMR x 1.4 inactive men and women (this applies to most people in the UK)

BMR x 1.6 moderately active women

BMR x 1.7 moderately active men

BMR x 1.8 very active women

BMR x 1.9 very active men

Example Calculation

Moderately active man aged 25 and weighs 75kgs requires

15.1 x 75 + 692 x 1.7 = 3103kcals

Final Note

Finally remember that you need to spread your calorie requirements over the course of the day, with generally lighter meals in the evening as your Metabolic Rate fluctuates over the course of the day dropping as you go to sleep at night, but equally increasing for a period of time after exercising (how long depends on type of exercise and intensity).