What is BMR?
BMR stands for Basal Metabolic Rate, which along with RMR ie Resting Metabolic Rate is a term used to describe the energy requirements of the body at rest. The difference between the two lies with the set of conditions in which the measure is taken. The conditions for measurement of BMR tend to be more stringent than for RMR e.g. the individual has to have had 8 hours of sleep, and fast for 12 hours prior to BMR measurement.
Is my BMR all my calorie needs for the day?
BMR accounts for the calories required for basic functions such as breathing, the circulation of blood, and maintaining body temperature. Anything we do above this e.g. sitting, walking, running, will increase our energy requirements. The more active we are the greater our energy requirements for the day.
Basal Metabolic Rate
Accounts for between 50 – 75% of your daily energy needs
Varies by age, by weight, by height, by gender
Varies by the amount of lean mass that you carry
Decreases with age because we slow down and lose muscle mass as we get older
Use of Equations
In clinic or at home settings, we use equations to calculate out BMR or RMR. This helps us to understand our caloric needs, without having to have a lab assessment. If I calculate my BMR and RMR using my weight, height, age, and being female I get:
BMR = 1259kcal per day
RMR = 1162kcal per day.
So you can see there is just a slight difference between the two. From here, I will refer to BMR as it tends to be the term used most often.
How do we know how many calories we need in 24 hours
To estimate our total calorie requirements we can use different systems, depending on the type of individual concerned. For the general population we make use of a factor which suggests the amount of calories an individual might need across a day.
For a sedentary worker ie a person who works in an office and goes about their daily life without much of anything else, we use a factor of 1.4. This refers to a Physical Activity Level. The more activity is absorbed into that person’s day, the higher the factor we use. For example we might use 1.6 for an individual who runs for a half an hour three times per week, but is also a sedentary worker.
If I consider myself a sedentary office worker who is not doing much activity, perhaps achieving 8 – 10k steps per day, my total requirements look like this
1259 x 1.4 = 1762kcal per day
If I consider myself as sedentary, achieving 10k steps per day, but active in an exercise class perhaps 3 times per week or more, my requirements increase
1259 x 1.6 = 2014kcal per day
What is a metabolic equivalent?
For the most part a dietitian will use clinical judgement and experience to assess the factor to make use of when calculating an individual’s energy requirements. But if the individual is seriously active, then a different system will be employed in an effort to be as accurate as possible. In this case a sports dietitian will use metabolic equivalents.
Metabolic equivalents or METS are estimates of the energy used by the body during particular activities relative to the basal metabolic rate. Running might have a MET value 8.0, this means the body is working 8 times as hard as it normally does at rest, but only across the minutes the individual is actually running. METS are based on consumption of oxygen and have particular values for different sporting activities. As a sports dietician I will use these MET values and apply them to the number of minutes an individual is performing a single sport, or range of sports, to assess their energy requirements.
This way of working is slightly more complicated, but more applicable when an individual is very active.
What are UK Physical Activity Guidelines
Physical activity guidelines describe exercise generally as light, moderate or vigorous; this really refers to what the MET value will look like for that type of exercise.
Light = < 3.0 metabolic equivalents (METS) per minute
Moderate = 3.0 – 5.9 METS
Vigorous = ≥ 6.0 METS
Current UK physical activity guidelines suggest we all need to carry out at least 30 minutes of moderate activity per day ie warm but not sweating, on at least five days per week. If we cannot make this happen we can work out more vigorously ie 3 times per week for 25 minutes each time – but this time we do have to sweat.
If you would like me to help you with your sports nutrition or weight change needs, please get in touch. You don’t have to be an athlete to enjoy the numbers game.