I just got asked how many calories you should burn when you exercise on Twitter. The answer is that it depends on several things. “It depends” would fit into 140 characters, but that’s not very helpful. How it depends is probably more like 14000 characters. Hence this blog post.
I’m going to assume that fat loss is the objective here. (Some might find the word fat a little crude, but I think it’s important to be mentally clear on that you want to lose fat as opposed to muscle. )
We all know fat loss is all about calories in, calories out. I am also a big advocate of that it does matter where those calories come from and how you burn them, because most people also want to feel good and eat tasty, filling meals as well as be in good shape in addition to losing fat. (Few of us would consider a life in which we eat five candy bars upon waking and nothing else for the rest of the day, then make time to walk slowly for hours for exercise as desirable. But if calories in, calories out were really all that mattered in practice, you could.) But setting that aside for this post – because that’s way too much to cover in one go – I’m just going to focus on the calorie “accounting” – how do you figure out how many calories you should be burning in a workout?
Before I get too far, I do want to point out to other accuracy sticklers out there that ultimately, all numbers involving calories in or out are estimates of some sort. If you are used to hard sciences or engineering data, this is all pretty fuzzy. Accept it and live with it. It’s just darn tricky to measure something that occurs physically spread out in your body on a cellular level to the same kind of accuracy you can measure the elemental composition of a material, in large part because you always have to measure some indirect marker of metabolism. There is no contraption you can stick into a million cells to directly measure what the Krebs cycle in you is doing. Uncertainties can be as large as 100 calories, so don’t fret about measuring to a fraction of an ounce what you eat or about the variability of energy expended while running with your knees high versus shuffling. This is a massive time trap that will not help you actually be more accurate. (I have spent months in it.) Call within 100 calories even. Maybe even 200.
How to estimate calories in I think most people are familiar with – you count calories to find out your daily caloric intake. Yes, yes, I know, you’ve heard it a million times. I wasn’t excited about it at all, because I thought it seemed overly restrictive and obsessive. And who wants to be obsessive? While there certainly are people who go there (see accuracy note above as an antidote), you don’t automatically have to. The truth is, you can’t really know how you’re doing in the calorie deficit department if you haven’t actually counted all your calories, estimated your base metabolism, and how much you burn in exercise. If you don’t know either one (or neither!) of calories in or calories out, you don’t really know if you can expect to lose weight. Walking around expecting to lose weight when in reality you have no reason to do so is probably the definition of weight-loss frustration. Remember, self-torture isn’t a weight-loss tonic. Being uncomfortable is not a sure sign that your diet/exercise program is working. Track the numbers, and even with the 100-calorie uncertainty you’re going to know if you’re closer to 1500 or 2000 calories a day. You don’t have to do it, as long as you don’t mind not knowing if you can expect to lose weight or not.
If you want to get in control of your weight loss, find a way to count the calories. There are sites for it, like FitDay, DailyPlate or SparkPeople, and apps like Lose It! or FatSecret. Figure out what works for you so you have a number to work with.
Now, for the calories out part, assuming you’re not just measuring it with a Bodybugg. There’s two sub-parts to figuring this out without having to log how much time you spend doing what every hour of every day. (Some advocate that approach, I just don’t think anyone is going to do that in addition to counting calories.) Let’s break it down.
There are many ways to calculate this answer, called the resting metabolic rate (RMR). I’ve picked the easiest and the most accurate here and I’ll leave it to you to pick the one you like best. (You may also have heard of basal metabolic rate or BMR – RMR is basically BMR + tiny movements allowed. BMR is measured when people pretty much don’t move at all. I think RMR is measured under conditions that are more like what you actually do when you are resting. Take note, super-dieters – going below this number is starving yourself to death, even if you don’t exercise at all.)
The easiest: Multiply your weight by 10. (Or add a zero to the end, same effect.) So if you weigh 176 pounds, you need about 1760 calories to just survive with minimal movement. One kilo is 2.2 lbs – so if you weigh 80 kg, your weight in pounds is 80kg *2.2lbs/kg = 176 lbs. (Source: The P90X nutrition guide)
The most accurate: If you know your fat percentage, you can calculate your lean body mass and then use the Cunningham formula. If you measure body weight in pounds, you’ll have to convert it to kilograms. (It’s only fair – kilogram users have to convert to pounds using the easy method above. Or use a calculator.) The Cunningham formula is
RMR = 500 + (22*LBM), where LBM is lean body mass in kilos.
Example: My body fat percentage is 22.6 right now and my weight is about 145 lb. One pound is 0.45 kg, so my weight in kilos is 145*0.45 = 65.25 kg. 22.6% of that is fat and the rest is lean body mass. If 22.6% of me is fat, then 100% – 22.6% = 77.4% of me is lean body mass. In kilos, that would be 65.25 kg * 0.774 = 50.5 kg.
So now I’m ready to apply the formula.
RMR = 500 + (22*50.5) = 500 + 1,111 = 1,611 calories
You have to admit, slapping on a zero on your weight in pounds is pretty darn easy. But why is the Cunningham formula the most accurate? Because it works with the lean body mass, which is what burns most of your calories. There are formulas that just use your weight, but fat and muscle burn different amounts of energy at rest – so your body composition matters. The more athletic you are, the bigger the difference between the formulas that use only weight and the ones that use lean body mass. (There is a ‘sister’ equation for BMR that also uses LBM called the Katch-McArdle equation.) So if you’re doing to bother with an equation, why not get it as right as you possibly can?
I’ve actually had my RMR measured a few months ago, after round 1 of P90X. It was 1610 (within 100 calories) calories/day when I weighed 150 lb and was 25% body fat (i. e. 50.6 kg lean body mass). The P90X nutrition guide method gives 1500 for my RMR at that weight. The Cunningham formula gives an RMR of 1,614 calories. Both are consistent with the measured 1610 plus/minus 100. (In other words, the measurement says my RMR is between 1510 and 1710 calories/day.) But look – a month into round 2, I’ve lost fat but virtually no muscle. So the P90X nutrition guide method would peg me at 1450 cal/day rather than the 1611 cal/day (that is still consistent with the measurement) that the Cunningham formula gives. So as your body fat creeps lower, the super-simple method is going to come in too low. 150 cal/day is a snack’s worth – enough to be the difference between me going hungry or being satisfied.
If you’re a construction worker, you clearly burn more calories than someone like me, who mostly sits at a desk or is just walking around doing her job. However, I haven’t seen any formulas for calculating how many calories it takes to do your job other than if it’s a desk job. Perhaps that is because few construction workers find themselves trying to lose fat. Anyhow, just like in the last section, I’m going to present two ways of calculating this – one easy, one more complicated but potentially more accurate. (I say potentially, because by common sense it should be, but unlike the equations above I’m not aware it’s been proven.)
The easy way: Multiply your RMR by an activity factor from the table below, from a 1996 paper from McArdle et al. (Haven’t found a complete reference, so I don’t know from what journal.)
|1.2||Sedentary||Little or no exercise and desk job|
|1.375||Lightly Active||Light exercise or sports 1-3 days a week|
|1.55||Moderately Active||Moderate exercise or sports 3-5 days a week|
|1.725||Very Active||Hard exercise or sports 6-7 days a week|
|1.9||Extremely Active||Hard daily exercise or sports and physical job|
Example: My hybrid P90X-half marathon training program has me exercising 6 days a week, pointing to very active. But what about my intensity? I exercise what feels like pretty hard – heart rate 150 or above, which is 97%+ of my theoretically estimated max. (Although either my heart rate monitor measures high or the formula doesn’t apply to me – I’ve seen it measured at 165, which is more than the formula would predict.) I’ll go with very active.
My RMR was 1611 cal/day. I picked an activity factor of 1.725. That gives a total calorie burn of 2,779 calories/day.
The potential problem here is that how many calories you burn depends on not just how intensely you exercise, it depends on how big you are – how much mass you have to move around while you exercise. These numbers must assume some body mass, and you have no idea of how close yours is to that of the study’s subjects.
The potentially more accurate way: Use the McArdle table activity factor for sedentary individuals to account for your job, running errands, and watching TV. Then, find out how much your exercise burns, and start adding it all up. But don’t forget that calorie numbers often are gross, meaning that they consist of both what it would have taken you to just power your organs while sitting still as well as the part that’s directly due to the exercise. If you want to go this route, you need net calorie burns – not gross. You already figured out how much just living and going to work takes – if you just add gross calorie burns to this, you are counting some calories burned twice! For everything that isn’t running, the best solution I’ve found is to look up the calorie burn and subtract off what you burn just sitting or resting. (There are many other calculators, and judging their accuracy can be a little difficult sometimes.) To find out what you’d have burned just sitting, take your RMR and divide it by how long you exercised.
Example: My RMR was 1611 cal/day. With an activity factor of 1.2, I will burn up 1,933 calories if I don’t exercise at all. But I do! So let’s add yesterday’s 5-mile run. For net calorie burn, it’s 0.63*145 per mile (where 145 is my weight in lb), so 0.63*145*5 = 457 total for my run. Adding that to the 1933 I already have, that comes to 2390 for my total calorie burn for the day.
If it had been a P90X day, I would have entered my weight into an activity calculator and looked up the numbers for 50 minutes of vigorous weight lifting, which according to this calculator is 334 calories. There are 1440 minutes in a day; so I burn 1611/1440 cal/minute, which is 1.12 calories a minute. 1.12 calories a minute times 50 minutes is 56 calories. So, since the 56 calories for resting were already counted as part of the 1,933 calories I burn before exercise, I only burned 334 – 56 = 278 calories extra. (That seems a little low, and I wonder how close P90X is to whatever they mean by vigorous weightlifting. But you see how the math works.)
I don’t have a measurement of calorie burn during exercise to do a definite reality check with here, but I believe the 2390 number over the 2779 number. I eat about 1800-1900 calories a day. If I truly needed close to 2800 calories/day, I’d be running a 1000-calorie deficit. Shouldn’t I be, you know, hungry or something? And losing weight at a whirling, nearly dangerous, rate?
While I am losing fat, I lost 2.5 inches from my waist in a month and 2.4 points of body fat, which apparently was about 5 lbs of fat total. If you run the numbers, that works out to be an average daily deficit of ~650 calories. If I add 650 to 1800, I get 2450 – only 60 calories off calculation number 2, so close enough for me to call even. (remember the 100-calorie rule.) I think what may have happened with that table is that the study was only done on men. That’s not uncommon, and the results for men don’t always apply for women, but are reported as if they do until someone proves otherwise.
Alright, now that you know your calories in and your calories out, you can start playing with the numbers to see what you think you can do. I’m sure you know that 3500 calories is equivalent to a pound of fat.
When you start knocking that out over 7 days (I know, I know – but we’re approximating anyway, remember? Close enough but simpler than calculating deficits for each day separately), you get the following deficit-fat loss relationships (assuming you are also maintaining your muscle mass and only losing fat):
|Fat loss/week||Fat loss/month||Deficit|
|0.2 lb||0.8 lb||100 cal|
|0.4 lb||1.6 lb||200 cal|
|0.6 lb||2.3 lb||300 cal|
|0.8 lb||3.1 lb||400 cal|
|1.0 lb||3.9 lb||500 cal|
|1.2 lb||4.7 lb||600 cal|
|1.4 lb||5.4 lb||700 cal|
|1.6 lb||6.2 lb||800 cal|
|1.8 lb||7.0 lb||900 cal|
|1.9 lb||7.8 lb||1000 cal|
(You shouldn’t be trying to run more than a ~1000-cal deficit.)
Now we’re getting to the actual answer to the question, believe it or not! So since you know your calories in (I’m going to leave diet changes out of this to keep the focus on how you know if you’re exercising enough), look athow many calories you burn staying alive and going to work compared to your daily caloric intake. (The same? Is one smaller than the other? What’s the difference?) Then look at how fast you’d like to lose weight and see what kind of an average daily deficit that’s going to take (assuming you exercise 6-7 days a week). How many calories you should burn during exercise is however many it takes to get your daily calorie burn the deficit’s worth above your daily calorie intake. Tadah!
Ok, maybe that was clear as mud. Let’s three examples.
Example: How many calories should I be burning to meet my fat loss goals? Well, let’s see. My goal is actually in terms of body fat percentage, but I’ll try to cut down on confusion by not showing how I made it a ‘lose X pounds’ goal under the assumption that I won’t gain or lose muscle mass. (Even though I’d like to get more!)
I eat about 1800-1900 calories a day. Without exercise, I burn 1,933 cal/day just powering my organs, eating, sleeping, and working. So I eat roughly what I burn in a day, and my amount of fat will stay the same if I don’t exercise.
If my lean body mass were to stay the same, I’d need to lose 8.1 lbs to meet my goal. Since my daily calorie intake and burn are nearly the same, I just need to exercise away whatever number of calories I want to get under by each day. If I wanted to burn it off in 90 days, I’d need to exercise off about 400 calories a day (8.1lb/3 mo = 2.7 lb/mo; from the table, the closest value is 400 cal with about 3.1 lb/mo.)
Example 2: Slightly more complicated case. Karla wants to lose 15 lb in 90 days. She eats about 2200 calories a day, and burns about 2400 calories a day without exercise. In this case, even without exercise she has a 200-cal deficit. However, to make her goal, she’s going to have to create a 700-calorie deficit – 500 calories more than just her diet provides. So for Karla to lose the 15 lb in three months, her exercise sessions are going to have to burn 500 calories a day. (700-200=500)
Example 3: Another more complicated case. Dave wants to lose 5 lb in two months. He also eats about 2200 calories a day, but only burns 1900 calories without exercise. This means he eats 300 calories more than he burns already! For him to meet his goal, he’s going to have to create a 300-calorie deficit. But because he eats 300 calories more than he burns without any exercise, his workouts have to burn both the extra 300 calories he eats and another 300 to make the 300-calorie deficit! So Dave’s workouts should burn 600 calories a session. (If I were Dave, this math would motivate me to take another look at my diet. 600 calories per session is going to be tough.)
Instead of worrying about daily numbers, look at a week at a time. Here’s that table again, but with weekly calorie deficits instead:
|Fat loss/week||Fat loss/month||Deficit|
|0.2 lb||0.8 lb||700 cal|
|0.4 lb||1.6 lb||1400 cal|
|0.6 lb||2.3 lb||2100 cal|
|0.8 lb||3.1 lb||2800 cal|
|1.0 lb||3.9 lb||3500 cal|
|1.2 lb||4.7 lb||4200 cal|
|1.4 lb||5.4 lb||4900 cal|
|1.6 lb||6.2 lb||5600 cal|
|1.8 lb||7.0 lb||6300 cal|
|1.9 lb||7.8 lb||7000 cal|
Add up your weekly calorie intake and your weekly calorie burn if you didn’t exercise, then compare those numbers. Figure out how you’re going to get to the weekly calorie deficit you need to be at to meet your goal. (Note: you may be about to find that you’re asking the impossible. If so, this will tell you what you can expect within what you’re willing to do.)
Example: Jane works out three times a week and wants to lose 5 lb in a month. That means she needs to create a roughly 4200 calorie deficit per week. She eats about 2,000 calories a day and burns about 1,800 calories a day living and working. Her daily excess is 200 calories, which adds up to 1400 calories in a week. To first get rid of the extra 1,400 calories she eats and then create the 4200 calorie deficit she needs, she will need to exercise off 1,400+4,200 calories, which is 5,600. Since she has three days to do it in, each workout would need to burn 5,600/3 = 1,867 calories a session. That’s probably impossible, unless she is an elite athlete with time to train all day – but only for three days. Jane just isn’t going to lose the 5 lb in a month.
A reachable number with an intense hour a day is around 400 calories for most normal-weight women. Let’s work it the other way around. 400 calories, three times a week is 400*3 = 1200 calories. That’s still less than the 1400 extra calories she eats a week. Jane is probably going to have to deal with her diet in addition to worrying about how many calories to burn when she exercises. If she can come out about even before exercise, though, she could create a 1200 calorie/week deficit. That’s pretty close to the 1400 calories that would give a 1.2-lb fat loss a month. At her current exercise rate, Jane can lose the 5 lb but is going to have to wait about 4-5 months. (Note that Jane will lose the weight so slowly, watching the scale like a hawk is probably only going to drive her nuts.)
If that isn’t fast enough for her, she has two options to really speed things up: add more exercise days or start creating a deficit even before she considered exercise. Doing both will be fastest, of course.
I realize that all this might seem impossibly complicated if you’re not used to crunching numbers all the time. If the last time you had to do this was 10 years ago, understandably it’s more effort than if you can reach out a hand and get the scientific graphing calculator (because you use it all the time) like scientists and engineers. I think anyone can do it if they want to, but I’m realistic. You may not want to.
If you don’t want to run the numbers, I’m happy to do it for you. If you can get me your daily calorie count, your weight (ideally your body fat percentage too), and your fat loss goal, I can run the numbers for you. Just drop me a line at teresa at fityoginirunner.com.