Numbers you need to know
BMR: Basal Metabolic Rate – This is the number of calories your body burns just keeping itself alive. So things like your heartbeat, breathing, all the ongoing internal repairs, your organs carrying out their functions…basically what you would burn if you were in a coma.
RMR: Resting Metabolic Rate – this is very similar to BMR but I prefer BMR because it is slightly more conservative and therefore less likely to be overestimated, or at least not by as much. RMR is what the body burns at rest, like sitting or laying around. There is such a thing as REE (Resting Energy Expenditure) which is a small amount of extra energy expended by your body at rest. RMR would include things like keeping your posture, getting up to go to the bathroom, moving at all like reaching for a glass of water or even turning over in bed. So BMR is a better calculation because RMR is still including activity, even a small amount, and BMR calculators are already at risk of overestimating. Unfortunately, to know your REAL BMR you would have to pay to be tested in a clinic. But the more you know about your body composition (fat % vs muscle %) the more accurate your calculations will be.
Here’s the basic equation (Harris-Benedict)
Women:
BMR = 655 + (9.6 × weight in kg) + (1.8 × height in cm) – (4.7 × age in years)
Men:
BMR = 66 + (13.7 × weight in kg) + (5 × height in cm) – (6.8 × age in years)
Another formula which is thought to be more accurate is the Mifflin St. Jeor
Men – 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5
Women – 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161
If you know your lean body mass or body fat %, you can use the Katch McArdle formula
BMR = 370 + (21.6 x Lean Body Mass(kg) )
Lean Body Mass = (Weight(kg) x (100-(Body Fat)))/100
A calculator that includes your body composition is more likely to be closer to accurate, since having a higher body fat % means burning less calories at rest, because muscle burns more calories than fat. All the more reason not to skip those weights in your workout. 😉
Knowing your approximate BMR (or exact, if you’re able to shell out the cash for a clinical test) is important in choosing your calorie total. Personally, I don’t like to eat more than my BMR because I think mine is a bit lower than average, I’m concerned about overestimation, and I just don’t trust measures of calories burned with exercise. I like to keep track of them, but if my Fitbit or online calculator says I burned exactly 276 calories doing whatever exercise, I’m not going to assume that’s true and actually plan my food around it. Besides, I don’t exercise to make caloric “room” for more food. However, a lot of people say they have been able to eat just a few hundred cals under their TDEE (explained below) and lose weight so they must fit exactly into the statistical average these equations were made for, or maybe be underestimating. It’s not something I bank on. But it works for some and it is good to know anyway, whether or not you use it to determine your daily limit. I would expect it would be more accurate for extremely active people vs sedentary, who might have a lower BMR due to body comp anyway.
TDEE: Total Daily Energy Expenditure – this is the total amount of calories you burn each day, consisting of your calories burned through activity and/or exercise on top of your BMR. Calculators will usually use a BMR calculation, and then ask you to rate your activity level on some kind of qualitative scale (for example, “sedentary, light activity, moderate activity, strenuous activity” or similar.) I like to always use “sedentary” or maybe “light activity” just to counteract any tendency to overestimate. It’s helpful to try a few settings, to compare and get an idea of how many more you might burn by increasing exercise. As an alternative to a calculator, you could track your exercise calories during an average week or month, take an average, and add this to your BMR.
Here is a popular TDEE calculator that accounts for a lot of factors: https://tdeecalculator.org
There are calculators for BMR and RMR also, just look it up online.
I hope this helps you set your calorie goals and better estimate your projected weight loss. To estimate your projected weight loss, you can use these calculators
https://www.precisionnutrition.com/weight-loss-calculator
https://www.losertown.org/eats/cal.php
Honestly, a lot of the time I just choose my calorie limit based on a number that sounds good to me. 600 just seems like an almost perfect number, and is sustainable for a decent period of time. I also like 800. If I have a lot to accomplish and am exercising a lot I can do 1000 or even 1200 as a top limit. A lot of people in ED/weight loss community swear by the “TDEE minus 500” thing though. That reminds me, 3500 calories in a pound of fat. Use that to calculate projected loss based on your deficit. So 500 cal deficit times 7 days would be a pound a week. Whatever works for you. The important thing is that you stay in a calorie deficit, whether this is daily, or an average trend, for example people who allow a day over TDEE every week or some days every month. As long as the average is a deficit trend. It really depends on how quickly you want your weightloss, how low an intake you can maintain, what will satisfy your own personal ana or mia needs, and what your health concerns may be, if any.
