Understand how metabolism and weight loss work

In today’s post we are talking a little bit about metabolism and how we can make it work in our advantage when we want to lose fat. So, if you are looking for some tips and tricks on this topic bear with me for the next 15 minutes and I guarantee that at the end of this article you will have an optimal and smart approach to losing weight.

The idea of writing this article came to me after I did an article about the three body types – ectomorph, mesomorph, and endomorph – and how differently each of react to dieting and weight loss programs in general.

This is because the metabolism, which we will see that is in fact the main driver for weight loss.

The energy IN versus energy OUT story

As you know already, losing weight loss it’s all down to energy in versus energy out or calories in versus calories out. If you want to lose weight you need to eat less calories than you burn and this works for the majority of the people for most of the time. But what if you are already down to just 1,500 kcal a day, staying hungry all the time, doing 5 cardio sessions a week and still not losing any weight?

Reducing your calories even more will be extremely hard and probably is not going to help.

People with slow metabolic rates are going to struggle with weight loss, while people with fast metabolic rates are going to struggle to put on weight.

This is where what I am about to tell you comes in handy. What’s a slow metabolism? What’s a high metabolism? Can we speed up our metabolism? What is metabolic damage and how it can be undone?

But before we get down to it let’s give metabolism a definition.

weight loss metabolism

What is metabolism?

To put it in simple words, metabolism is converting food into energy, with the purpose of maintaining life. It’s what our bodies do in order to sustain the biochemical reactions that take place at cellular level, breaking nutrients into the substances that keep us alive and kicking.

That’s a very basic and simplified definition that will do for the purpose of this article, but if you want the more complex stuff you can check out the long version definition.

Let’s introduce another term that I’m sure you’ve heard of before: basal metabolic rate (BMR) or the metabolic rate. BMR excludes any physical activity such as weight lifting or any type of exercising and it also excludes digestion of foods (known as the thermic effect of food).

BMR is measured in complete resting state and represents the amount of energy need by the human body just to maintain life. The BMR is most of the times measured in kcal and varies quite a lot from person to person based on several factors such as age, fat-free mass, fat mass, sex and circulating thyroxine (thyroid gland related). There is scientific evidence behind each of these factors.

Yet things get even more complicated than that. BMR can vary substantially even in individuals that have the same age, gender and body composition. It’s genetic and there is not very much you can do about it.

What internal factors influence metabolism?

According to this study the most important factors that affect the BMR are fat-free mass, fat mass and age. However aproximately 26% of the variations in BMR couldn’t be explained by any study so far. BMR just varies in people that apear to be identical for no reason.

This means that a 200 pounds 15% body fat male can have a BMR of 2,000 kcal/day and another similar person can have a BMR of just 1,480 kcal (26% less) with no scientific explanation behind this variation.

A higher BMR means that you will burn more calories (by doing nothing) and a slower BMR means that you will burn fewer calories.

Here is the influence of known factors on BMR based on the study mentioned above:

  • 63% was explained by fat-free mass (FFM)
  • 6% was explained by fat mass (FM)
  • 2% was explained by age
  • 2% depends on subject effects
  • less 1% was analytic error
  • 26% was unexplainable

As you can see most of the variations in BMR will depend very much on fat-free mass (63%) – which is very much influenced by the muscle mass and the next big chunk (26%) couldn’t be explained. It is just the way nature works. If you are having trouble understanding terms such as fat free mass or fat mass please check out this article on body composition.

Before we move on I want to stress the fact the FFM, hence mucle mass has a great influence on BMR and on each individual’s ability to burn fat. That’s why you see natural bodybuilders that can stay lean by eating 2,800 – 3,000 kcal a day.


Total daily energy expenditure (TDEE)

As I said at the very beginning of this article, BMR or metabolism is the main driver for weight loss, representing 60 to 70% of the total daily energy expenditure (TDEE). Here’s the formula for TDEE:

TDEE = BMR (60-70%) + TEF (10%) + Activity (20-30%)

Therefore a healthy BMR level is very important no matter your goals (weight loss or weight gain). A good BMR will help with getting in caloric restriction without starving to death each day. It’s really important to take all actions necessary to keep your BMR at a heathy level.

Calculating BMR

According to the studies I read, the average BMR measured in males and females is around 1,500 kcal per day. There is not an exact way you can use to determine the BMR unless you get tested medically, but the following formulas should be close estimations:

  • BMR for Men = 66.47 + (13.7 * weight [kg]) + (5 * size [cm]) − (6.8 * age [years])
  • BMR for Women = 655.1 + (9.6 * weight [kg]) + (1.8 * size [cm]) − (4.7 * age [years])

The formulas are different in males and females because of the different muscle mass levels. Usually, BMR is much higher in bodybuilders and generally in fit people because of the increased muscle mass, hence increased fat-free mass.

Based on your activity levels you can use the Harris Benedict formula to calculate your TDEE:

  • TDEE = BMR * 1.2 (Little/no exercise)
  • TDEE = BMR * 1.375 (Light exercise)
  • TDEE = BMR * 1.55 (Moderate exercise (3-5 days/week))
  • TDEE = BMR * 1.725 (Very active (6-7 days/week))
  • TDEE = BMR * 1.9 (Extra active (very active & physical job))

Let’s take me for example. I am 31 years old, 85 kg and 184 cm, so the formula would read like this:

  • BMR = 66.47 + (13.7 * 85) + (5 * 184) − (6.8 * 31)
  • BMR = 66.47+1,164.5+920-210.8
  • BMR = 1940.17 kcal/day

I train 5 day a week at moderate intensity and I am pretty sedentary outside the gym, so I will go with the 1.55 multiplier to calculate the TDEE.

  • TDEE = 1,940*1.55 = 3,007 kcal/day

I have a pretty accurate idea of what my maintenance level is because I’ve been tracking calories and measuring weight changes on a daily bases for many months now. I am maintaining my weight at about 2,500 kcal a day, so in my case the formula is a bit off.

That should be the 26% variation that studies couldn’t explain. I guess that my BMR must be a little bit on the slow side, compared with the average.


The wrong approach to weight loss

There are two common mistakes people do when they try to lose weight.

  1. Aggressive caloric restriction
  2. No reverse dieting

Let’s talk about each of the two a bit. This part is really important, make sure to get it right.

What most people do when they want to lose weight? Everybody is suddenly changing their diet to just one apple and two glasses of water per day and starts hitting the treadmill like crazy.

Let’s sit back and analyze things a bit. First you cut back on calories really aggressive, so the energy IN is getting really low. Then, you boost your activity level and the energy OUT sky rockets. This results in big negative energy balance which will shock the body and as a result the metabolism will slow down, making it harder or even impossible for you to lose (any more) weight.

Your body doesn’t know you want to lose weight. Your body knows that it needs to survive and that it needs food to survive and it will do just that. The goal of your body is to balance the energy in with the energy out.

Restricting calories too aggressively will trigger a thing called metabolic adaptation. This has been proven by studies and studies, so if you hear people saying that there is no such thing as metabolism slowing down on you when dieting they are talking crap.

The more calories you restrict the slower the metabolic rate will become. After a couple of weeks of excruciating hunger you will not see the results you wanted, you will give up the diet, and start binge eating.

With a slowed down metabolism and with an avalanche of calories coming your way, the fat gains will come in no time and you will end up fatter than you initially started your diet. This is not a position you want to be in.

At the end of the so called diet you will have a damaged metabolism and 10 extra pounds. Now, let’s see what would be a more wise approach to weight loss.

Man running on a treadmill
Man running on a treadmill

The right approach to weight loss

As you remember, the metabolism is the main driver of weight loss and your success will rely on it, so make sure you take good care of it and you’ll be good. The preparation starts before you even start dieting.


The best position to start dieting from is from a high caloric maintenance level. If you are eating a decent amount of food and you are maintaining your weight (even if you are overweight) you are in a good spot and you can start cutting. It means that you metabolism is running smoothly and is able to keep up (balance out) all the calories you are taking in.

If you are in a caloric deficit and not losing any weight you want to up your calories a little bit (while maintaining your current weight). This is also known as reverse dieting in the fitness industry and the purpose of it is to slowly and gradually (100-200 to kcal each week should work fine) get out of a caloric deficit while allowing our metabolism enough time to catch up. This should get your metabolism up to speed.

Another proven way of increasing metabolism and creating a deficit easier is to workout – if you aren’t already. Weight lifting increases muscle size which naturally increases BMR and you also burn more calories just by simply getting active – which will allow you to eat more while still being in a caloric deficit.


Once you are ready to start your weight loss program you want to start it gradually so that your metabolism doesn’t “notice” it right away, or doesn’t see it as a life threatening situation.

My recommendation is to start off by cutting just 200 to 500 kcal a day depending on what your TDEE is. Usually you should cut with more than 20% of your TDEE. This should result in a weigh loss of up to 2 pounds each week which should be sustainable for 2-3 months for most people.

Diet should consist of high amounts of proteins and medium carbs if you are working out, but also fats – which are thought to boost or fix metabolism.

Monitor you calorie intake and weight regularly to see if you are making progress. Once you achieve your goal you should start reverse dieting, don’t just jump back to maintenance or bulking phase.

Use weight training and cardio training as a way of placing yourself in a negative caloric balance while still eating decent amounts of food each day.

Hope this has been informative; let me know if you have any questions, comments or any other type of constructive feedback.

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