So lets get on with the blog post..........
If I had a pound for everytime i have recently been asked "how many calories do you eat a day?" I'd be a richer man. This question is usually followed by "do you think that would be right for me?" I then have to explain that I don't know because I don't know certain things about the person............
Being as focused as I have been for the last few months on achieving significant weight loss and increased fitness levels, I have become very familiar with the concept of counting calories in and measuring calories out (calories burnt through activity). The purpose of this exercise is simply to understand and manage the amount and type of food consumed to ensure that sufficient food is consumed to provide fuel for training without eating more than is actually required and therefore avoiding gains in % body fat levels. Measuring calories in and out can also be used to good effect where simple weight loss is the aim.
Measuring calories consumed and calories burnt through activity is fine but it becomes very much less effective if the incorrect " net calorie target" is used. So how do you know what the correct number of calories is? I'm sure many people just pick a number and try to lose weight or maintain weight using what is in effect a guess as their calorie target, or worse still they may know somebody who has lost weight by sticking to a calorie target and they use that persons calorie target because it worked for the other person.
What we actually need to know and understand is how many calories does our body need each day in order for it to function healthily without gaining or losing weight. Once we know this number we can then work out what our calorie target is going to be taking into account our sports and weight loss goals.
Basal metabolic rate, or BMR, is the minimum calorific requirement needed to sustain life in a resting individual. It can be looked at as being the amount of energy (measured in calories) expended by the body to remain in bed asleep all day!
BMR can be responsible for burning up to 70% of the total calories expended, but this figure varies from one individual to another. Calories are burned by bodily processes such as respiration, the pumping of blood around the body and maintenance of body temperature.
BMR is the largest factor in determining overall metabolic rate and how many calories you need to maintain, lose or gain weight. BMR is determined by a combination of genetic and environmental factors, such as:
- Some people are born with faster metabolisms;
some with slower metabolisms.
- Men have a greater muscle mass and a lower body fat percentage. This means they generally have a higher basal metabolic rate.
BMR reduces with age. After 20 years, it drops about 2 per cent, per decade.
- The heavier your weight, the higher your BMR.
Example: the metabolic rate of obese women is 25 percent higher than the
metabolic rate of thin women.
- The greater your Body Surface Area factor, the higher your BMR. Tall, thin people have higher BMRs. If you compare a tall person with a short person of equal weight, then if they both follow a diet calorie-controlled to maintain the weight of the taller person, the shorter person may gain up to 15 pounds in a year.
- The lower your body fat
percentage, the higher your BMR. The lower body fat percentage in the male body
is one reason why men generally have a 10-15% faster BMR than women.
Starvation or serious abrupt calorie-reduction can dramatically reduce BMR by up
to 30 percent. Restrictive low-calorie diets may
cause your BMR to drop as much as 20%.
- Physical exercise not only influences body weight by burning calories, it also helps raise your BMR by building extra lean tissue. (Lean tissue is more metabolically demanding than fat tissue.) So you burn more calories even when sleeping.
It's all well and good knowing that their is something called BMR, but how does the ordinary man or woman on the street work out what their own BMR is?
There are many different formula's you can use to determine your caloric maintenance level by taking into account the factors of age, sex, height, weight, lean body mass, and activity level. Any formula that takes into account your lean body mass (LBM) will give you the most accurate determination of your energy expenditure, but even without LBM you can still get a reasonably close estimate and a reasonably close estimate has to be better than guessing how many calories your body needs?
A reasonably accurate method for calculating the number of calories a body requires to maintain existing weight is to BMR using multiple factors, including height, weight, age and sex, then multiply the BMR by an activity factor to determine the actual daily calories a body needs. BMR is the total number of calories your body requires for normal bodily functions (excluding activity factors). Remember, this includes keeping your heart beating, inhaling and exhaling air, digesting food, making new blood cells, maintaining your body temperature and every other metabolic process in your body. In other words, your BMR is all the energy used for the basic processes of keeping the body healthy and keeping you alive.
For people who regularly participate in sport or are in structured training programmes, it is very important to remember that the higher your lean body mass is (or the lower the % body fat figure is) the higher your BMR will be. This is very significant if you want to lose body fat because it means that the more muscle you have, the more calories you will burn. Muscle is metabolically active tissue, and it requires a great deal of energy just to sustain it. It is obvious then that one way to increase your BMR is to engage in strength or weight training in order to increase and/or maintain lean body mass. In this respect it could be argued that strength training helps you lose body fat, albeit indirectly.
Well this has turned into a very long post and I can hear you all shouting at the screen now "just tell me how to do the calculation and stop rambling on about all the other stuff" ok, here we go, the Harris Benedict equation is a calorie formula using the factors of height, weight, age, and sex to determine basal metabolic rate (BMR). This makes it more accurate than determining calorie needs based on total body weight alone. The only variable it does not take into consideration is lean body mass. Therefore, this equation will be reasonably accurate in all but the extremely muscular (will under estimate caloric needs) and the extremely over fat (will over estimate caloric needs).
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)
Note: 1 inch = 2.54 cm.
1 kilogram = 2.2 lbs.
You are female
You are 30 years old
You are 5' 6 " tall (167.6 cm)
You weigh 120 lbs. (54.5 kilos)
Your BMR = 655 + 523 + 302 - 141 = 1339 calories/day
Now that you know your BMR, you can calculate how many calories you need to consume each day based on your known levels of regular exercise/activity by multiplying your BMR by your activity multiplier from the chart below:
Sedentary = BMR X 1.2 (little or no exercise, desk job)
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)
Extr. Active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, i.e marathon, contest etc.)
Your BMR is 1339 calories per day
Your activity level is moderately active (work out 3-4 times per week)
Your activity factor is 1.55
Your total daily calorie requirement = 1.55 X 1339 = 2075 calories/day
So, now we have arrived at a reasonably accurate estimate of how many calories our body needs to remain healthy which takes into account our normal lifestyle and regular activity levels, we can now look at how we adjust that figure to meet our personal weight and fitness goals. That, I think should be a subject for a separate blog post, as this post has ended up being a bit longer than I intended.
As always thanks for taking the time to read the (very long) ramblings of the Pixie and hopefully you will be able to pop back to the blog in the future to see what else the Pixie has learnt on his journey to l'etape 2013.
Dha weles diwettha