Want to gain weight? Want to lose weight? Want to recover faster from an injury or illness? Want to just plain feel better?
It all comes down to energy balance, a fancy way of describing how much energy you’re giving your body compared with how much energy your body needs. If you give your body more energy than it’s using (positive energy balance) it will store that energy either as fat, or as muscle, provided you get enough protein and train like a demon to stimulate the growth. If you give your body less energy than it’s using (negative energy balance), weight loss will occur. This doesn’t always mean fat loss though – if you aren’t using enough muscle, your body will happily break down protein (read: lean muscle mass and organs). In fact, if your energy intake is low enough, your body will happily break down protein and leave your fat stores as untouched as it can. Obviously this is not a desirable outcome.
See, as smart as we think we are, there can be quite a substantial disconnect between our bodies and our brains. We might know we have a big dinner coming up, or we’re going out for a special occasion, and so we might skip a meal to save up the calories for that occasion. The problem with this is that our bodies have no idea that this big, calorie dense meal is coming up. They just recognize that they aren’t getting any energy in… and to make sure they can physically survive as long as possible, they will keep as much energy in reserve as possible. Without enough stimulus – i.e. training – to tell your body to hand onto its muscle mass, that will turn into a fuel source and leave your fat stores as untouched as possible.
So if energy balance is important, we should probably have some idea of how much energy we need. To get a absolute and conclusive figure, this would mean spending some serious time in a lab hooked up to some machines. This is clearly beyond most of us. But we can get a fairly accurate estimate, using any number of equations. One of the most common equations estimating energy output is the Harris-Benedict equation, which estimates our resting metabolic rate (RMR) – they energy we need just to stay alive:
Harris-Benedict equation for RMR:
Men = 66.5 + (13.75 x weight in kg) + (5 x height in cm) – (6.76 – age in years)
Women = 655 + (9.56 x weight in kg) + (1.85 x height in cm) – (4.68 – age in years)
Some people apply an Activity factor to these results to determine a more accurate measure of energy output. I first found this on T Nation, spelled out here for all of us newbies by Canadian strength coach Christian Thibaudeau, who is not only world-famous as a strength coach, but also possibly because he looks strikingly like Vin Diesel.
Anyway, I see a lot of merit in the use of an Activity factor. Even though I’ve never found any research supporting this (though it’s possible I’m just looking in the wrong places) I currently use it with all my clients, particularly athletes, and will continue to do so until Dr. Berardi tells me otherwise!
I’m interested though, in seeing trying it with a different RMR equation: the Mifflin equation for RMR. The Precision Nutrition text brings some interesting figures to light, mainly that the Harris-Benedict equation estimates the RMR of only 69% of non-obese people to within 10% of their actual lab-tested RMR. On the other hand, the Mifflin equation estimates the 82% to within 10%. So while you’re not guaranteed to be right on (or even close), you’ve got a better chance with the Mifflin equation. It’s enough to convince me to swap, and I’m interested to see what the differences will be, both on paper and in terms of effectiveness.
Mifflin equation for RMR:
Men = (10 x weight in kilograms) + (6.25 x height in cms) – (5 x age in years) + 5
Women = (10 x weight in kilograms) + (6.25 x height in cms) – (5 x age in years) – 161