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The Calorie Myth


There is a lot of confusion about the concept of "calories" when it comes to diet and exercise and the problem is made far worse by well educated people (including some MDs) making grossly misleading statements such as: "a calorie is a calorie".  While technically a calorie is always a calorie from the perspective of a physicist or chemist, when viewed from the perspective of health, exercise and weight management, the meaning of "calories" shifts somewhat and one calorie of food or exercise is NEVER just one calorie! You cannot as some have claimed, simply reduce your food intake by 500 calories per day and expect that you will lose one pound every week (one lb of fat contains 3500 calories), in fact you may not in some cases see any measurable weight loss.  You also cannot simply exercise an extra 500 calories each day and count on weight loss either.  The reason is simple, even though the physical value of a calorie is a constant, the manner in which your body treats the calories is not, it varies continually:

  • Every food you eat (from a very simplistic view) consists of some mixture of one or more of the following: proteins, fats, and carbohydrates, each of which contributes to the total calories. Depending on the specific proteins, fats and carbohydrates involved, your body requires varying amounts of energy to process and absorb the food you eat, so eating 200 calories of ice cream delivers more energy to your body than eating 200 calories of celery once the food has been digested, because the amount of energy your body expends to extract the same number of calories from celery is much higher.
  • Some sources of calories in food cannot be adequately processed by your body so calories cannot be fully extracted (this is generally the case for high fiber foods).
  • Your body reacts differently to different parts of the food, and requires certain fats and proteins in order to keep operating. By varying your fat and protein intake (as well as the types of fat), you can actually cause your metabolism to speed up or slow down.  Assuming you are eating what would otherwise be considered a reasonable diet, if you reduce your fat intake below 15% of your total calories, you will most likely begin to see some slow-down, and if you allow it to drop below 10% for any period of time, not only are you likely to see a significant slow-down, but you could potentially cause serious health problems. This is one of the many reasons that seriously low fat diets don't work for most people, if you reduce your calorie intake by reducing the fat in your diet too far, you are potentially going to slow down your metabolism to the point that it partially or completely offsets the reduction in calories you are eating.
  • Your body constantly adjusts its metabolic rate based on what you eat, how much you exercise, how often you eat, how often you exercise and various other things including your particular genes. One major factor: does your body think it has been starving recently? This can cause your metabolism to shut down and work in an energy-conserving mode while attempting to store as much food as possible as fat.  This is your body working to protect you in times of famine, even though if you are reading this, it is highly unlikely you will ever experience real famine. If you have ever been on a diet and started having problems with your toes and fingers being chronically cold or getting light-headed when you stand up, it is quite likely you were suffering from the effects of your body trying to protect you from starvation by trying to conserve energy.
  • Over time, the human body generally becomes more efficient at performing any physical task which is repeated on a regular basis. A couple of years ago I started running into town to pick up my mail once or twice a week (6.8 miles / 10.9 kilometers round trip). I use the term "running" very loosely here as I was not in particularly good condition and it was very slow. Using a watch with a heart rate monitor I tracked the calories burned on these runs, and over the course of a few months, the calories burned went from over 1200 for the round trip to less than 700 for the same run. My weight did not change significantly during this time, and while my speed improved over this period, it was nowhere near enough to account for the difference.  The efficiency of my body at performing this run was the primary change. Because of this effect, basic differences in physical conditioning, as well as genetic differences between different people, the tables which give the approximate number of calories burned per hour performing various exercises are almost completely useless.
  • When you burn extra "calories", depending on the circumstances, your body has a number of choices of fuel:
    • Glycogen - a high-energy on-demand fuel reserve the body maintains for when a quick response is needed. This is a fairly limited reserve and once it runs out the body will have to switch to something else.
    • Food you just ate - any food in the blood stream / being fed in from the digestive system (carbohydrates, proteins, fats)
    • Stored fat - that excess body fat that most people are trying to get rid of, one pound of fat is roughly 3500 calories of fuel, so to lose one pound of fat, you must burn an extra 3500 calories. Unfortunately, it's not quite that simple (see "Muscle" below).
    • Muscle - yes, your body views your muscles as another fuel source, but it is not a very good one, one pound of muscle only provides about 600 calories of fuel; however, if your body thinks you are starving, it may start burning large quantities of muscle in order to reduce the number of calories you burn each day (the less muscle you have, the more slowly you burn off calories). The more rapidly you lose weight, the more likely your body is to start burning muscle for fuel, particularly if you are losing more than 1% of your body weight per week.

Ultimately, what all this means is that there is NO simple formula for calories in versus calories out.  In theory you could gain weight, lose weight, or stay at the same weight, eating the exact same number of calories, and performing the exact same exercises, just by changing which foods you eat and/or the timing of your eating and exercise! If you really want to trash your body, do all of your exercise first thing in the morning, wait until just before bed, then eat all of your calories for the day in one massive high-carbohydrate meal (I would suggest eating something like white bread or cake for maximum effect).

So how did I / can you successfully lose weight?

  1. Focus on fat loss, not weight loss
  2. Exercise on a regular basis - six days a week for me.
  3. Carefully measure all the food you eat and get a good list of calorie content of foods so you know exactly how many calories you have consumed each day.
  4. While this is not strictly necessary, things were much easier once I found a way to accurately track the calories burned each day.  For me this was a "Polar F6" heart rate monitor / wrist watch.  By wearing this watch and the heart rate monitor strap, I found it could accurately track how many calories I burned during any activity (this is a built-in feature of this and many similar heart rate monitor watches).  By wearing it each time I did any significant exercise, I knew how many calories I had burned.  I also tried wearing it for 24 hours to see how many calories I burned in a typical day without any particular exercise (this did start to give me a rash where the heart rate strap was around my chest).  Wearing it for common tasks I performed on a regular basis also helped me to get a feel for the total calorie burn each of these activities involved to help me with my daily tracking.  There are some really cheap heart rate monitor watches where you have to press a finger on a certain part of the watch to measure your heart rate.  These are absolutely useless for calorie tracking, you need one that monitors heart rate continuously and provides a "calories burned" reading.  So far as I am currently aware, all of these use a chest strap to track heart rate.  There are many expensive ones with fancy features, but a number of them which are more than adequate are available for well under $100 US.  Note: when using these watches, it is important to remember they track TOTAL calories burned during the workout, not additional calories burned (you would have burned some calories during that period of the day even if you did nothing), so you need to remember that when computing your calorie deficit for the day.
  5. Try to run a calorie deficit of 500 to 1000 calories a day for no more than three days straight, then try to eat as many calories as you burn on the next day (or even a little more than you burn).  I actually just structured my life around things I was already doing, most weeks I ate out with friends for Tuesday lunch and had dinner with friends on Saturday, so I designated those days as the ones where I would eat as many calories as I burned (since I was far more likely to consume extra calories at these meals), and ran a deficit on the other days.  Note: I think it is important that you run at least a 500 calorie deficit, because errors in our measurements of calories eaten and burned can add up to the point where fat loss is not achieved, particularly since we tend to fudge the numbers in favor of allowing ourselves to eat more and exercise less.  If you push it over 1000 calories in a day or go for more than three to four days in a row with a deficit, your body will think you are starving and start trying to protect itself by slowing your metabolism.

Doing these things allowed me to quickly achieve my fat loss goal, but it required that I have good information and a plan structured to ensure I succeeded:

Hopefully, whatever you decide to do, having a better understanding of "The Calorie Myth" will help you to achieve your fitness goals.



I wonder why there seems to be no wrist watch monitors which measure calories used throughout the day - not just during exercise.Shannon mentions she thought this was essential, as it is not possible to calculate it 'on paper',  but she had to use a chest strap to do it. Whenever I ask if one is available people look at me as if I am mad!Is there some technical reason which makes this difficult?I've read all your on-line articles and I think they are the best I have ever read.Sincerely,                 Peter

Hi Peter,

The problem with creating a monitor without a chest strap is the sensors (aside from my writing, I have a great deal of experience with the development of medical devices). The chest strap picks up the electrical signals at the heart and relays them to the watch. In order to eliminate the chest strap, you must find a way to measure the heart rate both reliably and continuously at the watch. While it is possible to measure heart rate by taking your pulse on the arm (electronic blood pressure cuffs do this), it is much harder to do without using an inflated blood pressure cuff which is not something you can use continuously. I can think of ways it could be done, but (so far as I am aware), none of them could be powered by a watch battery.

I'm glad you enjoy my writing. Not that it matters, but I'm actually a man.



This isn't necessarily true. I found that the difference in calories is not about reducing fat. Increase in fats and protein equaled an increase in satisfaction.I chose to reduce carbs and made quite a change in my once purely vegetarian diet to do so. Since fat burns hotter, I can actually eat as much as I need to keep satisfied and I still lost extra weight.So much easier for me than trying to satisfy my body with less and less food.Nutrition counts as much as calories too.Sarah

You have misunderstood what I said. I did not say to reduce the fat in your diet, rather you should focus on reducing the fat in your body. Too many people focus on weight loss when the issue is how much excess fat they are carrying around. Simply focusing on losing weight could result in muscle loss, dehydration, and even reduced bone density, all of which are detrimental, but look good when you are standing on a scale. If you are doing it right, you will lose the fat but keep the muscle, bone and water.