Metabolism and Energy expenditure

Ok, from the previous blog post we know what our weight is and how to figure out its distribution. The only thing that remains is to figure out how many calories you should be eating to get the body composition you want.

To do this you must understand your metabolism, and how it works.

First a few terms you will need to understand as I will be using the shorthand for much of the article.


·         TDEE, Total Daily Energy Expenditure. This is the amount of energy used to keep you the same weight when you add your BMR to the number of calories burned during your daily activities and exercise.

·         BMR, Basal Metabolic Rate, which is the amount of energy required to keep you alive in a coma like state. This is approximately 70% of your TDEE.

·         TEF, Thermic Effect of Food, this is the number of calories burned to break food down into its constituent macronutrients. Usually works out to around 10% of calories consumed

·         NEAT, Non Exercise Activity Thermogenesis, how much you burn doing all the little things, like getting up from your chair, fidgeting, climbing stairs, walking around the office, doing your job. Basically, anything that you do during the day that involves moving. This accounts for approximately 15% of your daily energy expenditure.

·         EAT, Exercise Activity Thermogenesis. This is the number of calories burned during your workout. This makes up the rest of your energy expenditure for the day, at about 5%.


How to determine your BMR

Every tissue type in the body has a specific metabolic capacity, in other words the amount of energy it burns at rest.

According to this study, (1) the metabolic rates of specific tissue types were proposed as;

·         Cardiac tissue (the heart) burns 440cal per kg per day.

·         Liver is 200.

·         The brain burns 240.

·         The Kidneys are 440.

·         Skeletal muscle burns 13.

·         Adipose tissue (fat) burns 4.4.

·         Residual mass (skin, intestines, bones and lungs) has a metabolic rate of 12 calories per kg per day.

The combination of the above make up the calories your body burns in a 24 hour period and only stops when you die, so the myth that your metabolism slows or drops at a certain time of day is utter nonsense, what does change though is your activity level. However, our bodies don’t work on an hour to hour basis when it comes to calorie requirements, if they did, we would have died out a long time ago.


Based on the information of the metabolic requirements of different tissue types, we can calculate your BMR; there are a couple of ways to do this based on body composition.

If you know your lean (fat free) mass you can use the Katch-McCardle equation

370 + (lean mass in kg x 21.6)

If you don’t know your lean mass, then you can use the Mifflin St Joer equation which is different between men and women.

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.  

Both of the above methods suffer slightly in accuracy with the Mifflin St Joer equation being found to be accurate to within 10% (2)

As a result, my advice would be to adjust the result down by 10% by multiplying your answer by 0.9.

With this adjustment in mind, the equations would now look like this;

Men                 (10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) + 5) x 0.9
Women            (10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) – 161) x 0.9

Also Mifflin St Joer doesn’t take body composition into account, which means that 2 people of the same age, height and weight but very different body fat percentages will end up with the same result. To adjust for this I use a chest to waist ratio for men and a waist to hip ratio for ladies. For example, if a guy’s chest is 1.3 times bigger than his waist, it’s fair to assume the guy has a lower body fat percentage than a guy with a waist that is 1.1 times bigger than his chest and therefore he requires more calories.

The gold standard of accuracy when determining BMR is indirect calirometry. Basically you wear either a hood or a mask that has a pipe running into a machine that measures the exchange of oxygen and carbon dioxide to determine how many calories you are burning. Unfortunately, this is mostly only available in sports science labs or metabolic clinics. 

Establishing calorie requirements.

Your calorie requirements are based on the energy balance equation. Which is calories in vs calories out and looks like this

tdee pic.png

For a simplified version we look at your work activity, training intensity and training frequency.  Sedentary individuals will have a lower TDEE than those who are highly active despite possibly having a similar or higher starting BMR. There is a widely used chart that gives you a number to multiply your BMR by.

activity level drawing.png

So now you know your BMR and can estimate your activity level, you can work out your TDEE.

To do this simply multiply your BMR by your activity level multiplier to give you a total.

For example,

The calculation for an individual with a BMR of 2300 who is very active will look like this

BMR equals                          2300 calories

Activity multiplier equals   1.725

TDEE                                       2300 x 1.725 = 3967.5 calories 

Now if we have an individual with the same BMR, but they are sedentary, it would be a different outcome;

TDEE                                       2300 x 1.25 = 2875 calories

This is a difference of 1092.5 calories. So putting these two people on the same intake would not work.

Remember though, your TDEE is the number of calories required to maintain your current weight, if you want to lose body fat, you need to create a calorie deficit, if you want to gain muscle, you need to create a calorie surplus. What you will need to do though is find the best ratio of macronutrients to achieve a body composition that favours lean, toned muscle over body fat.


To increase lean muscle, a good starting point is to create a 500 calorie surplus; this should give your body the energy it needs to support the repair and growth of muscle tissue. The Holy Grail is to try to gain muscle without gaining too much body fat, another goal is to avoid the dreaded plateau, where muscle growth halts. This usually happens when you have gained a significant enough amount of muscle so that the surplus you were in is now only adequate to maintain your size. To avoid this it is vital to check your body composition regularly and increase your calories accordingly.


The same applies to losing body fat, once you know what your calorie requirements are to maintain your current size and activity level; you want to create a calorie deficit just big enough to enable fat loss to occur. The trick here is to preserve as much lean muscle as possible during this process, so you end up leaner for your weight, rather than just smaller and lighter with the same body fat percentage.

I’m not a fan of absolutes in training, but where there are no medical issues, such as thyroid dysfunction/ autoimmune disease, this is one exception to that rule;

                NEVER reduce your calorie intake lower than your BMR.

The trick when trying to program for fat loss is to find a balance between low enough calories to elicit the burning of stored fat, but not so low that the body does one of the following,

1.       Reduce muscle mass, (muscle is nearly 3 times more metabolically expensive than bodyfat and as a result, will be the first casualty when cutting calories too low), this has the effect of then reducing your BMR, meaning you now burn less calories than before.

2.       Reduce NEAT (see definition above), if you’ve ever drastically reduced your calories at the same time as increasing the amount you exercise, you will have experienced this. Your body, in a bid to preserve energy, starts to slow down the amount of fidgeting you do, you’re less inclined to move when you get home, more likely to us the lift, rather than stairs. You won’t want to walk as much, maybe you don’t play with your children as much either, all because you feel constantly fatigued.

When these two things happen, as they typically do, your TDEE can drop so significantly, that the calorie deficit you put yourself in, is now the amount of calories you need to stay exactly where you are, this is when a lot of people give up, day in, day out, you are going to the gym, counting calories, keeping to your deficit, but nothing seems to work. Sound familiar?

To stop this from happening, we have several cards that we can play, 

·         The first, is to reduce calorie intake, nothing drastic, just enough to kick start the process.

This can be as simple as eating a few less biscuits on each tea break, reducing your portion sizes by a quarter, changing from full fat to low fat alternatives. Simple swaps that mean you don’t have to make an entire lifestyle change overnight.

·         Next, we can add in exercise if you aren’t already doing it, something simple like a 45 minute walk every day or every other day, whichever suits your lifestyle and schedule.

·         We can start increasing non exercise activity, take the stairs instead of the lift, get off one stop earlier on the tube or bus, get a standing desk. Anything really that just increases your energy expenditure during the day.

·         Diet breaks, this is something that is gaining a bit of traction at the moment, the idea that you have several weeks of calorie restriction, followed by a week or two of eating a maintenance number of calories for the weight you are at that point. From the research, this kind of protocol is showing excellent long term results as you can essentially diet for longer periods of time with far better compliance levels than if you were severely restricted for weeks or months on end.

Try not to play all of these cards at the same time and if you can, get yourself to a position where you can start your calorie deficit at a much higher point. What I mean by this, is that you will likely have more success if you can start burning fat at an intake of 2200 calories which gives you room to drop when things slow down, than you will if you start at 1200 calories, where there is no where to go when things slow down.

If you have a target weight or body fat percentage in mind, what you do when your reach that goal determines your long term success and whether or not you keep off the weight you just lost, or gain it all back as fat with a little more to boot.

The worst thing you can do is to go back to the calories you were consuming before you started your diet, at the new, lighter bodyweight, it stands to reason that your BMR will be lower, especially when we consider that it is the number of calories used to maintain your body at rest. Less body mass, less energy required.

Once you have achieved your fat loss target, you will need to calculate your new BMR and subsequent TDEE for your current activity level and look to increase your calories slowly back up to this amount. This is best done over the course of 6-8 weeks and is known as a reverse diet. To do this simply figure out the difference between your maintenance requirements and your current intake, divide the result by 6 or 8 depending on how long you want to take and add that number to your intake each week until you have returned to your maintenance amount. Keep your macronutrient ratios the same during this process too.




Dan Thomas