Basal Metabolic Rate (How Much Should I Eat?)

Since the bootcamp is Monday and Wednesday this week I took Tuesday off in order to manage my workload a little just in case I ran out of gas for Wednesday’s class. I have been mulling over the content and format for this session and I think once the new gym area is set up I will take a leaf out of the Crossfit world and try to incorporate some strength / max weight work into the class before some lighter MetCon work. For today I don’t think it will be possible even though I suppose I could do squats, the gym and the placement of the equipment isn’t ideal.

That’s later, for now I want to answer another question I get very often… How much should I eat. Once you introduce people to calories and the idea that your body requires a certain amount to function then they get curious and wonder how much they need. It’s an inexact science still, and the numbers depend on a lot of factors. We know that it’s not necessarily calories in Vs calories out since there are “good” and “bad” calories but still there are guidelines that can be used to establish a starting point.

Your body is made up of muscle, bone and fat. Your muscle and bone require significant calories to maintain their state and as such contribute to your basal metabolic rate which is the minimum amount of calories your body needs to fuel itself just sitting still. If you fall below this number, your body will catabolize itself to make up the shortfall either by burning stored fat or by burning lean tissue. Which one it picks is partly due to your diet composition, partly down to hydration levels and partly due to hormonal balances. But to keep this basic lets just say that in order to maintain your lean mass you need to eat a minimum amount of calories. Since our body is only using fat as a “just in case” source of energy we will ignore it in our calculations, especially since it requires basically no calories to exist. So in order to calculate our calories we need to know our lean mass. This is easily done by getting your bodyfat measured with calipers, a fat scale or a water tank dip. These methods will all give you differing accuracies as far as the results but in the case of the scale, it’s a good tool to use on an ongoing basis to give you a start point and an average measurement. For me as I stated the other day my numbers look like this:

Weight 231 lbs or 105Kg (1Kg=2.2lbs)
Bodyfat 15%
Lean Mass (total weight x .85) = 196 lbs or 89.1Kg
Fat Mass (total weight – lean mass) = 35 lbs or 15.9Kg
you could also do Fat mass as total weight x .15 and get the same results.

So I calculate my BMR (not the bullshit BMI!) with the following Cunningham Formula:

500+(22xLean Mass in Kg) which for me is 500+(22×89) = 2458 calories

We take this BMR number and multiply it by a variable between 1.2 and 1.9 to get our caloric requirements for the day. The difference in activity will determine whether you use 1.2 or 1.9 or a number in between.

Again using myself as an example my calories required for the day would be BMRx1.2 up to BMRx1.9 or in numbers:

2458×1.2 = 2950 calories
2458X1.9 = 4670 calories

For most people who are not competitive athletes and spend less than 4 days a week in the gym you are probably good around the 1.2-1.4 mark. For someone who works out vigorously at least 4 days a week (note there is no time duration here) then you can probably bump that up to 1.5-1.7. There are probably very few people in the general population who would need to be in the 1.7-1.9 range.

So in my example I would start out eating around 3000 calories a day and see what happens to my weight, my energy levels and my tolerance for either hunger or the ability to eat that much fruit and veg! The key is to give yourself a place to start and then to adjust as time goes along. As long as you are measuring what you are doing and what is happening, you will know what adjustments to make. But you need to know what the numbers are if you are going to make informed changes.

In the end, do something, have some information about what you are doing because something beats nothing every time!

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