Friday, March 02, 2012

Basal Metabolic Rate BMR

Basal Metabolic Rate or BMR (sometimes known as Resting Metabolic Rate or RMR) define your bare basic caloric need for the day. It is the theoretical number where it is the minimum you should consume to expand (or use) for vital body function such as the normal function of the heart, lung, kidneys, liver, gastrointestinal (GI) system, muscle, skin and reproductive organ.
Technicality and science/research aside, BMR are often used by doctors and nutritionists when determining an appropriate diet for overweight patients or people with illness.
With this understanding, BMR is the absolute minimal caloric need for a person if all they do is to sit down, do nothing but rest.
Caloric expenditure differs from person to person, with common denominator such as age, sex and your height. Ambient temperature of where the person is does effect the required BMR as well, with colder countries or condition generally requires additional caloric intake to maintain the body core temperature.
It is estimated that the hardest working vital organ in the body is the liver where it consumed up to 27% of the BMR. It also make sense as the liver singlehandedly processes all the chemical we take (alcohol, cigarettes, artificial flavouring, sugar, medicine etc). It is also no surprise that a person with damage liver typically will expire sooner than another person with vital organ illness such as damaged kidneys or palpitating heart.
The Harris-Benedict Study
Like mentioned in my previous entry, i made a lot of research myself back in 2003 and 2004 era and putting everything into Excel spreadsheet. Equations such as those from Harris-Benedict (1919) has been studied and read to understand the implication of the body physiological need versus the food we take. Harris-Benedict formula is the oldest longest formula ever derived for BMR and extensively used in many commercially (programmed) available weight scale and gym equipments.
You can propagate your own Excel sheet by using the formula below:
The Harris-Benedict equation for BMR:
For men: (13.75 x w) + (5 x h) - (6.76 x a) + 66
For women: (9.56 x w) + (1.85 x h) - (4.68 x a) + 655
Also, the Harris-Benedict method is at best estimation of Resting Metabolic Rate (RMR) where it overestimated by about 5%. It does not take into consideration other items such as the thermic effect of food. 
Thermic Effect of Food
By mean of that, if defines the eating (biting, chewing, swallowing) and processing (digestion, metabolism and storage) of the food we take. Protein requires up to 30% energy to be digested as compared to carbohydrate at about 15% and lipid at about 8%. 
Extra note on lipid -  if you take something that has a lot of fat, it requires less effort to be digested. Do bear in mind that a gram of fat has 9 calories - so, apart from requiring less energy to be digested, it provides more energy in return and will end up around your waistline faster!
On the average a figure of 10% is used to include this thermic food effect. Meaning, if you have a meal of 500kcal, 50kcal will be used to process the food. And if you want to replace that 300kcal burned running a fast 5km, you will need to take 330kcal to replenish that. 
The Mufflin Study
To potentially make the BMR more accurate, the Mufflin study was done and it takes into consideration the effect of protein, carbohydrate and lipid on the body's BMR. It also used a list of suggested factor to multiple with the BMR to ensure sufficient energy for the average person and their daily activities. Mufflin study is what i based my BMR on and it is slightly more acceptable for me due to the other consideration that was put in such as the level of activities and also the "Thermic Effect of Food" factor.
The Mufflin equation for BMR:
For men: (10 x w) + (6.25 x h) - (5 x a) + 5
For women: (10 x w) + (6.25 x h) - (5 x a) - 161
The study logic is based on the potential of  under eating that will effect metabolism and that is a bad thing to happen. A study subject on bare 800kcal to lose weight (possibly aneroxic) will have the metabolism lowered by 10% and potentially vital organ shutting down. 
So, instead of only limiting yourself the BMR to let the body function, they put in correction factor to buffer up the perceived energy requirement that you will potentially need to carry out the day's activity - and that is assuming you are planning to stay at your current weight. Someone with higher body mass (muscle) could afford a bit more caloric intake as muscles will burn more energy. This is not to be confused with someone that is heavy justifying that their "muscle" requires more "food", which is typical of wannabe bodybuilders thinking packing on mass is about adding on weight.
Below is my Excel sheet propagation of the BMR per Harris-Benedict and Mufflin.
I am currently running on bare BMR of 1596kcal according to Mufflin. However, i am using 1510kcal as my basis as i am trying to lose up to 1lb/week That is easily achievable by cutting down my caloric intake by 500kcal/day. I will need about 2000kcal to maintain my current weight at my current sedentary lifestyle (of little or no exercise and only desk job, which i do 5 days a week).
The secret to losing and eating healthily is to be aware of what you put in your mouth, and knowing what works for you, and what don't.
Armed with these information, try coming out with your spreadsheet and enters the numbers and formula as shared above and you will be surprised just how much you really need to take everyday to survive.
And yes, that one serving of Banana Leave rice with a fried chicken easily runs up to 800kcal or half of your daily caloric intake. That beef burger you just ate at the fast food joint cost you 700kcal with or without the cheese (as it makes no different by then). Of course these food are enjoyable - but you will pay the price of overeating and adding on weight when you don't planned to!
Next up: General caloric guideline for typical Malaysian Food.

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