I wanted to know how many calories I needed to eat to find my food deficit per day when I count calories as I eat. I also wanted to know how many calories I burn doing exercise so I can add that to my food deficit. I can then take these two numbers combined and count them against how much weight I need to lose, presumably all fat, times 4000 calories per pound of fat. This is where I came up with about a quarter million calories for my around 60 pounds I am in the process of losing. Here is what I found. (skip to the bottom if you want the short step by step version)
In order to know how many calories you burn during an exercise you need to know two things. First how hard you are working out in units called METS, and second your Basal Metabolic Rate (BMR) which is your personal multiplier. It is possible to determine it without these two numbers specifically, for example you might know how many watts you are producing and can therefore get to the same point. But, the formulas all have the components and could be separated out if you like to do algebra tricks just to show off. Often scientific studies are done where a specific form of exercise is measured and so you can use other things in your formulas like average heart rate. But this is only good if you accurately measure and know your own personal constants. For example, your VO2max, so that you can accurately predict how much oxygen is being consumed, hence you are again back at METS if you want to be.
METS, or metabolic equivalents, are how many times harder you are working out as compared to if you were doing nothing. This number has been found experimentally for all sorts of things. You need to have a sanity check of course, as you can do just about anything at various levels of activity. For example, I could vaccuum the house at a pace that was easy and at a pace that made me sweat. I could lift the chairs and move the sofa or just hit the center of the room. So if you see a number for vaccuuming you have to also make sure it is equivalent to some other exercise where you know the number is valid. Typically, mph numbers on a treadmill are accurate because so much has been done to study these values. So you look at a table of activites to determine the METS of your activity. You multiply this by your BMR (calories per hour) to get how many calories you will burn in an hour of that particular activity. Part of the METS calculation has to do with how many muscles you use. So this is why bike riding is fewer METS versus an elliptical trainer if you do what you percieve to be the same effort, more muscles are being used for the elliptical workout.
Basal Metabolic Rate is measuerd by getting a good night sleep and then while awake but not stimulated, that is no coffee, no stress, just sit and relax and breathe into the tubes tied onto your face as if nothing was wrong. The digestive system needs to be inactive, so, no eating while you sleep either (for 12 hours actually). It is measured directly by measuring the heat your body gives off, or indirectly, by measuring how much oxygen you consume which correlates nicely to the heat thing. There are many formulas for getting an estimate and they are all based upon trying to predict how much oxygen per body weight is going to be used while resting. It is measured as energy per time usually calories per hour is what you will want to calculate. There are many online calculators for this, the simplest one I saw was 11 times your weight for a man and 10 times for a woman. This one is incorrect though. This is per day so you must also divide by 24 if you want the hourly rate. There are two good equations to use for an estimate that gets you close to each other so either can be used. I substituded english units because, although the metric system is great, I don’t use it, and this is for me after all.
The Katch-McArdle formula is the same for men and women as it uses lean body mass, instead of weight, which is just subtracting 1 from the percent of fat, so 30% fat would use 0.7 in the equation (BMI is not body fat percentage by the way, it is a slightly higher number). The BMI to body fat calculators are not perfect so unless you know your body fat by a more accurate measure you might as well use the first method.
For me the numbers are 1845 and 1794.
This is not the number of calories we must eat to maintain our body weight, it is 1.2 times this because of what is called the thermic effect of food. Basically, it takes calories to digest food, so you have to eat 20% more than you thought to get the number you were looking for. Then of course this number assumes you sit around doing nothing all day, so you add calories for ALL activities if you want to see how much you need to eat exactly. Or in my case how muc of a deficit is created by eating less than this number. If you lead a very active life you might need to eat 90% more, or very sedentary is only 20% more. This activity of course assumes workouts and such, i.e a very active person works out 4 times a week. But since I don’t want this number, I want to put that in the workout deficit column, so I will just use 20%. Any extra in there is going to have to do with the general activities I do such as working at a desk is more than my BMR, walking around in a store, and even the EPOC is going to be a part of this calculation. For me all of this stuff is “gravy” for now. It is a non-zero number that gives me a boost, if I can keep the other stuff where it needs to be I can lose weight for sure, this just makes it come off a little faster than I could calculate. This is going to be true for anyone as well, even the sedentary person. There is just less “gravy”.
So 1845/24 gives me my METS 1.0 calculation = 77 calories per hour per METS. So if I engage in an exercise that is 10.0 METS, I burn 770 calories per hour. An example of 10.0 METS is running on a treadmill at 6.0 miles per hour. Here is the most complete list out there. If you do certain exercises often and want to calculate in a different way, you can certainly do that. But this is going to be as good as any method out there unless you are a research scientist or doctor and have access to all sorts of special equipment to measure it more closely.
So the short, step by step version is:
- Calculate your basal metabolic rate (BMR) using the formula above. (for me 1845 calories)
- Multiply BMR by 1.2 to find how many calories you need to eat a day to live a sedentary lifestyle. (for me 2214 calories)
- Divide BMR by 24 to determine a 1.0 METS. (for me 77 calories per hour per METS)
- Get a list that shows the METS equivalent (see above) or learn how to estimate it based on your activity level. Multiply these out times the hours to get your activity deficit. (For example, 30 minutes at 6 mph on the treadmill, (10 * 77 * 30/60) is 385 calories for me)
- To lose weight using the biggest loser method multiply your weight by 7 to get the number of calories to eat, subtract this from your BMR to find your food deficit per day. (for me 758)
- Add up all your deficits, you would include all activities not just workouts if you want an accurate number. (for me I am getting about 1000-1300 a day)
- Everytime you accumulate 4000, you lost a pound of fat. Be sure you are not working out in a way that will burn muscle off. This is why the biggest loser diet has you doing weights or resisitance workouts to be sure you are building or at the minimum maintainning muscle.