Total Daily Energy Expenditure (TDEE) is a measure of how much energy you use up during the day. It is composed of your Basal Metabolic rate (BMR), which is the energy you use up just staying alive and the energy you use doing everything else (walking, talking eating and exercising).
BMR varies from person to person and between the sexes. Men tend to have a higher BMR than women of equal weight and height. This is because men carry less fat than women do. Other factors that can affect BMR include:
· age, (BMR decreases by about 2% per decade after the age of 20)
· how your thyroid behaves (Thyroxin is a BMR regulator),
· diet (starvation diets reduce your BMR)
· internal temperature,
· external temperature,
· Physical exercise.
There are lots of ways to estimate TDEE but the most commonly used are:
· Quick and Dirty ( based on bodyweight )
· The Harris – Bededict formula
· The Katch – McArdle formula (where your lean body Mass hs been estimated)
We shall use the following example for the calculations:
· She is a 40 year old woman
· 5ft 4in = 1.63m tall
· 150lb = 68kg weight
· Body fat % = 32%
· She wishes to lose weight.
The Quick and dirty method:
· To lose weight = 12 – 13 calories per pound of bodyweight
· Maintenance = 15 – 16
· To gain weight = 18 – 19
In our example our lady should be eating between 1800 and 1950 calories a day to lose weight.
The Harris – Benedict (HB) formula (when you do not know your lean body mass)
As this method does not contain a variable for lean body mass it will underestimate the caloric needs of the extremely muscular and overestimate the needs of the extremely obese. First you must calculate the BMR and then add in your activity factor to determine TDEE
Men: BMR = 66 + (13.7 x wt in kg) + (5 X ht in cm) – (6.8 x age in years)
Women: BMR = 655 + (9.6 x wt in kg) + (1.8 x ht in cm) – (4.7 x age in years)
For our example BMR = 655 + (9.6 x 68) + (1.8 x 163) – (6.8 x 40) = 1343 calories/day
The activity multiplier is estimated as follows:
Sedentary = BMR X 1.2 (little or no exercise, desk job)
Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk)
Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)
Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)
Extremely active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, i.e. marathon, contest etc.)
Our lady estimates she is Lightly Active and so her TDEE can be estimated as 1.375 x 1343 = 1846 calories/day.
The Katch – McArdle (KM) formula (when lean body mass is known)
Men and Women BMR = 370 + (21.6 x lean mass in kg)
Our lady has had her body fat % measured at her local gym at 32% so her lean body mass would be 68 x (100 – 32)/100 = 46.24kg
So her BMR = 370 + (21.6 x 46.24) = 1369
Her TDEE using this formula would be 1.375 x 1369 = 1882 calories/day
You can see that both KM and HB formulas produce very similar results of 1846 and 1882 calories/day, but this is just TDEE and needs to be adjusted because our lady wishes to lose body fat. So how much could she reasonably reduce her caloric intake to lose fat? Well that’s like asking how long is a piece of string and would easily fill another article (hmm, I might write that one someday!) However, as a rule of thumb she could consider reducing her calories by 15 – 20% and increasing her exercise to include moderate workouts 3 – 4 times a week. She decides to reduce her calories by 15% and so her total calories using all three methods are:
· Q&D = 1800
· HB = 1569
· KM = 1600
I can’t say for sure if she lost weight on any of these diets but I’d like to bet her results would be better with the last two methods than the first. If you are trying to lose body fat; Good Luck.