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There are a lot of fads, a lot of gimmicks, a lot of diets, and a lot of tricks, but in the end there is only one factor that ultimately determines your weight: Calories. (See this study)
There a 2 pieces to the calorie puzzle: how many calories your body gets from food, and how many calories you burn. Any calories your body extracts from food that are not burned are stored for later. In other words, when it comes to calories, if you eat them, and you don't burn them, then you're going to wear them.
Simple enough, but it gets a little tricky figuring out how many calories you burn every day. You need to know both how many calories you burn when at rest (which is most of the time), and how many calories you burn when you are active. This is where BMR and REE come in.
If you were to spend the day just sitting there, then the number of calories used by your body to "keep the lights on" would be your Basil Metabolic Rate, or BMR for short.
BMR is pretty hard to measure. To do it perfectly requires requires a visit to a lab equiped with sophisticated calorimetry equipment. You'd also need quite a bit of time, since getting your body into a state of perfect rest actually takes a little work. Technically, you would need to fast for 12 hours or so first, so that even your digestive system is no longer active.
Resting Energy Expenditure (REE) is often used instead of BMR because it is easier to measure. REE is not quite as accurate, but generally comes up with a value that is pretty close to BMR, does not require fasting, and only takes a few hours in the lab. The terms BMR and REE are both intended to measure how many calories your body burns when it is 'idling,' and are often used interchangeably.
At Calorie Line, we use formulas to estimate your REE. These formulas do not require you to go to the lab, requiring only your age, gender, height, and weight. They do a pretty good job, if not perfect. For specifics, see below how we estimate REE & TDEE.
Ok, so you've had your REE measured (or estimated), and now you know that you burn a certain number of calories when at rest. But here is the tricky part. You have to put that together with the calories you burn when you are active. That is the total number of calories you burn each day, or your Total Daily Energy Expenditure (TDEE).
There are various ways to estimate TDEE -- we provide more specifics on how we do it below. But before getting into specifics, some more explanation on TDEE is warranted.
If you adopt a given calorie intake and exercise routine, over time your weight will drift towards that weight consistent with your TDEE and exercise routine. Consider "Sally," a 5'6" 35 year old woman who has a desk job. Sally goes for a brisk one-hour walk 3 times per week, and eats about 1780 calories on average daily. If you put all those numbers together, Sally's TDEE is consistent with weighing 150 pounds. In other words, if sally is currently 175 pounds, and she sustains her routine, her weight will slowly drift towards 150 pounds, then settle there. What if she is currently 120 pounds? Her weight would then drift up to 150 pounds, then settle there. Regardless of how many diets Sally goes on, she will eventually drift back towards 150 pounds as long as she maintains her current regimen when she is not dieting. If she wants to go lower, she will have to raise her TDEE (through exercise) or lower her food intake -- either way she needs a routine that is consistent with the TDEE of her target weight.
Trying to understand TDEE can be tricky. But it is crucial to understand TDEE if you want to also understand how calories effect your weight.
Consider Mary. She has hit her target weight of 130 pounds many times over the years, but always winds up floating back up to 150 lbs. The weight always comes back slowly but surely. Why? Mary always loses weight the same way, with her trademark system of exercise 5 days a week, skipping lunch, and not eating anything after 7pm. Eventually, she hits 130 lbs, and she starts to celebrate and relax. She's earned it.
Mary is 42 year old, stands 5 feet and 6 inches tall, and gets a moderate amount of exercise each week. When she's not on a diet, she eats about 1900 calories each day on average. A tad high for her height and the amount of exercise she gets, but really not too bad. Now that she's lost her 20 lbs, she wants to go back to her normal habits. Mary assumes that it is the occasional binge, or overly festive weekend, that typically causes her to put her weight back on. She only needs to binge a little less often, and she'll be fine, right? Wrong. Mary, at her height and age, should be getting about 1750 calories each day if she is going continue her moderately active lifestyle, and she is averaging 1900. Those extra 150 calories per day may not seem like much, but they are consistent with being 150 pounds. That is, her "Total Daily Energy Expenditure" (TDEE) is not that of a 130 pound person who exercises moderately -- those extra 150 calories per day add up to the TDEE of a 150 pound women of her height and age and exercise routine. Because of this, her weight will slowly but surely creep back up. Conversely, if she were to start out at 170 pounds (maybe due to an unusually indulgent Christmas season), her weight would simply drift down to 150 pounds. One way or another, given Mary's height, weight, age, and exercise level, her weight will just settle at about 150 pounds if she eats 1900 calories per day. That is the real meaning of TDEE.
Jump forward 6 months. Mary has put the weight back on. She is now back to 150 pounds. But she's grown tired of her trademark diet, and decides to go hunting around the web for a new diet -- one that lasts. Along the way she discovers TDEE. After playing around with the BMR and TDEE calculator on a certain web site, she discovers that to maintain a weight of 130 pounds, at her age and height and exercise routine, she would have a TDEE of 1745 calories per day. Mary decides that she is not ready to do her regular hard-core diet yet, but she is willing in the interim to limit herself to 1745 calories per day, just to get in the habit. It's only 150 calories. She starts tracking her calories on a certain, awesome web site, develops her calorie-counting skills, and sets a target date for starting her diet in a couple of months.
Alas, Mary is not able to get all the way down to 1750 calories per day, instead averaging about 1800. But a funny thing happens -- Mary's weight starts to drift down anyway. The scale does not lie. What is happening? By eating 1800 calories per day, Mary adopted the TDEE profile of a 5'6", 42 year old female of 140 lbs who exercises at a moderate level. At 1800 calories per day, Mary's body could not sustain a weight of 150 pounds, and began to drift down, slowly but surely towards 140 lbs, where it would eventually level off. If mary went on a diet, dropped all the way down to 130, but then resumed eating 1800 calories per day, her weight would then drift up to 140. Diets are temporary -- TDEE is for good.
After tracking her calories for a few months, Mary discovers that over the long term, it's going to be hard to eat less then 1800 calories per day on average. Sure, she can go a few days at 1700, or even less, but then she always breaks down with a little splurge. When she looks at her monthly averages, they always wind up at about 1800. That seems to be as low as it goes for her when she is not dieting. So now what? Oy, another diet is coming on. But then Mary remembers TDEE, and that there are two 'sides' to TDEE equation -- calories eaten, but also calories burned. Mary realizes that if she can increase her exercise so that that it amounts to an extra 50 calories per day, on average, then her TDEE will be consistent with that of a 130 pound woman, and her weight will drop. And so she does just that. And her weight drifts down.
Mary may not realize it at first, but with that small adjustment, she just got off the diet roller coaster. Having played around with her caloric intake, making minor adjustments, and with a little help from the TDEE calculator, she has zeroed in on a regime that works for her. She no longer thinks in terms of diets, but in terms of what her average number of calories and average amount of exercise need to be to hit her weight (in other words, what her TDEE should be). She knows that if she gets enough exercise, then she gets to have about 1800 calories per day. It does not matter whether her weight starts at 120 pounds or at 150 pounds -- regardless, her weight will simply drift towards 130 pounds.
Sometimes Mary does not get just the right amount of exercise, or limit herself to just the right number of calories. But by now she is more focused on weekly and monthly caloric averages then by daily numbers. She is no longer being played by fads and hucksters, and she isn't playing games with herself. Knowledge is power: she knows that a little increase in exercise for a few days next week will make up for a slip-up this week. Since she is tracking her calories, exercise, and weight, it's pretty easy to see when things are trending the wrong way, when action needs to be taken to ward off another full blown diet. Maybe she makes the adjustment, maybe she doesn't. But now, she knows what to do, and what is going to happen. She knows.
But it is one thing to know the adjustment you need to make, and another to make it. Does just knowing something make it happen? Well, the research is starting to pile up that says that the answer is yes, indeed it does:
At Calorie Line, we believe that there is a reason that all that record keeping helps. When you track your calories, exercise and weight, you are focused on the things that really effect your weight: calories eaten and calories burned. Real knowledge, real power. When it comes to your weight, we believe that tracking what you eat leads to the power of small adjustments, and to the power to get off the diet roller coaster.
According to a 2005 study published in the Journal of the American Dietetic Association (see references below), and a 2008 study published in the American Journal of Nutrition, the Mifflin-St Jeor formula is the best ways to estimate REE. For many people it will come within about 10% of your actual REE. It is, however, not as accurate for seniors, and does not work well across all ethnic groups. If you are a weight lifter with lots of muscle mass and no fat, these formulas don't apply. In other words, while these formulas are pretty good, they must be taken, so to speak, with a grain of salt. For most people, they will nevertheless give you a decent approximation of how many calories your body burns while it is at rest.
The Mifflin-St Jeor Formula for BMR:
Men: REE = 9.99 * (weight in kg) + 6.25 * (height in cm) - 4.92 * (age years) + 5 Women: REE = 9.99 * (weight in kg) + 6.25 * (height in cm) - 4.92 * (age years) - 161
The total number of calories you need each day to maintain a given weight is called Total Daily Energy Expenditure (TDEE). To calculate TDEE, you take your REE, then add the number of calories you burn from energy expended as a result of physical activity. Technically, you also need to factor in the "thermogenic effect of food consumed," or how many calories burned during digestion of food eaten. But that is overkill for our purposes, and we do not use it in our calculation.
Our TDEE calculator first estimates the REE for a completely sedentary person of the height, age, gender, and target weight that you provide in our calculator (see BMR/REE section above for info on REE). We then multiply that value by an activity multiplier of 1.2 to account for the fact that even a fairly sedentary person still burns some calories by being up and about. In other words, the formula for a sedentary person's TDEE that we use is:
TDEE of fairly sedentary person = REE X 1.2Unlike most TDEE calculators online, this is the only use we make of so-called 'activity factors' (see below). For the TDEEs of more active persons, we use the TDEE of a sedentary person as a baseline, and then add the calories burned by the physical activity in each scenario using this equation:
Calorie Burned = Weight (kilograms) * Time (minutes) * METThe MET values are taken from Compendium of Physical Activities: an update of activity codes and MET intensities
A premise of Calorie Line's weight, exercise, and calorie trackers is that the best way to figure out your TDEE is to measure how many calories you eat (as best you can), how much exercise you get, and what your weight is on a regular basis. Then, you can simply see how caloric intake and exercise effect your weight by looking at your graphs. But if you are just starting out at tracking your calories, then using our TDEE estimator can provide a guideline for coming up with goals for caloric intake and exercise.
Note that most TDEE calculators online make their estimation by multiplying your BMR (the calories you burn at rest) by an activity factor [FOR REFERENCE -- WE DO NOT USE THESE!]:
Sedentary = BMR X 1.2 (little or no exercise, desk job) Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk) Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk) Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk) Extr. active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, i.e. marathon, contest etc.)
Just about every TDEE calculator on the web uses the above classifications, called 'activity multipliers' or 'activity factors,' and multiplies them by estimated REE or BMR to estimate TDEE. These factors have found their way into books, online calculators, university lecture notes, and on and on. (See them for yourself)
So why are we the only ones that won't use them? Well, the first clue is that just about nobody bothers to say where these activity factors come from. It turns out they come from 'Energy and protein requirements: Report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series No. 724', a report released in 1985 by the world health organization (WHO). Even the WHO's own 2001 expert group doesn't sound too keen on these classifications anymore:
That is why we don't use the same TDEE formula as everyone else. We believe that what passed for 'lightly active' for an Italian man during the Great Depression and WWII may not pass for 'lightly active' today.
Our own skepticism towards the 'activity factors' originated from seeing discrepancies between the TDEE numbers that come from using the activity factors vs. the numbers we would expect from using the more recent MET values from the 'Compendium of Physical Activities: an update of activity codes and MET intensities' (see references below). For example, the activity multiplier technique predicts that a 43 year old, 6 foot, 200 pound male who is 'lightly active' (does sports 1-3 times per week) needs to average about 2535 calories daily to maintain his weight after multiplying his estimated REE of 1843 by 1.375. If we multiply the REE times 1.2, we get 2211, the number of calories that a very sedentary, but not bed-ridden 200 pound man burns per day. That same man then has to burn another 323 calories per day on average through physical activity for an overall TDEE of 2535. To put that amount into perspective, that same 200 pound man would have to jog (assume MET of 7 from the Compendium) for 70 minutes 3 times per week to burn that many of calories. Sure, it's doable, but it doesn't sound much like 'lightly active, sports 1-3 days/week' either, it sounds more like 'kind of sporty, physical activity 2-4 days/week,' which is not currently a category.
Of course, whether the multiplier is reasonable all depends on how much physical activity is achieved, not just during workouts but throughout the day. In our TDEE calculator, we provide a long list of different physical activity profiles combining work and recreation activity levels, and let you judge which most closely fits your lifestyle. In general, our TDEE calculator comes up with TDEEs that are a little bit lower than the ones that the WHO's activity multipliers come up with. As we become aware of research that better combines MET values for specific activities with overall estimates of TDEE, we will update our calculator accordingly.