Can Your Metabolism Break?
We speak a lot about fat loss at Triage. We have
had 1000s of clients successfully lose fat, and put out countless pieces of content to support people in their fat loss efforts (like our free nutrition foundations mega-article). Despite all this, it's clear that more information is unlikely to solve the public health crisis of obesity. We are eating ourselves to sickness and death, and the question is
often "what separates those who do gain weight in the modern environment from those who don't?".
The part of this question I am going to focus on today is that of
having a "broken metabolism". Many people think that their metabolism is somehow broken, or that it is disproportionately slow, and thus that there is something intrinsic about their physiology that prohibits fat loss. So, is this true?
Not quite.
If you, me, or anybody, can sustain a caloric deficit (eating less calories than are
expended each day), stored body fat will be used for energy, body fat percentage will reduce, and bodyweight will drop. That's true for an athlete, the average person on the street, and even those with hormonal and metabolic issues like diabetes or hypothyroidism.
What differs between individuals is the level of calories they may have to consume in order to be in a deficit, and also the rate at which they adapt to being in a deficit. Let's tease those two issues out...
(1) Slow Metabolism?
As you know from reading our nutrition foundations mega-article, energy expenditure (TDEE) can be broken down into the following categories:
- Basal metabolic rate (BMR) - the energy you burn at rest, just to keep you alive,
- Non-exercise activity thermogenesis (NEAT) - this is the energy you burn doing all the stuff you do each day that isn’t exercise, such as walking around, fidgeting and so on,
- Exercise activity thermogenesis (EAT) - this is
the energy you burn while doing exercise,
- Thermic effect of food (TEF) - this is the energy burned in the breaking down, digesting and assimilating of the food you eat.
Where people are generally focused when questioning the speed of their metabolism is BMR, as these are your underlying physiological processes, and it is true that there are some variations
here. The findings in this area extend back at least half a century, and we know that obese individuals actually burn more calories at rest (higher BMR), but that the more weight is gained, the lower the relative increase in BMR. This makes sense given that body fat is much less metabolically active than fat-free mass. Therefore, obese individuals technically have
FASTER metabolisms if looking at the absolute energy expenditure, which may seem counter-intuitive for some.
Where we may see a little more variation are in the other components of energy expenditure, particularly in response to over or
underfeeding.
(2) Metabolic Adaptations?
Viewing energy expenditure without reference to energy intake over time is quite superficial. What we really want to know is how people respond to over or underfeeding, as this is ultimately what determines the rate at which they lose or gain weight.
In this area, we encounter the topic of "metabolic damage", which posits that people somehow damage their metabolism by dieting, particularly aggressive or prolonged dieting. This is not without truth, but is grossly exaggerated. No matter how long you have been dieting for, or how aggressively you have dieted, you will continue to lose weight (or die) if you sustain a
caloric deficit. That does not change.
What does change is your underlying physiology, psychology, and subsequent behaviours. Generally speaking, underfeeding or dieting results in a normal, expected reduction in energy expenditure,
which can occur due to (1) reduced NEAT, (2) reduced TEF from simply eating less, (3) reduced bodyweight (contributing to lower NEAT, BMR, and EAT), and (4) reduced BMR and/or adaptive thermogenesis. Essentially, underfeeding results in the body becoming more conservative, so you may be less likely to move around as much, fidget, etc., you may feel colder (reduced thermogenesis), along with other changes. This does not mean your metabolism is broken or damaged, it's a normal response to
underfeeding, and is a reflection of your body doing its job.
The same thing occurs in reverse in response to overfeeding. With adaptions in each direction, we might then wonder if this varies between individuals, and it certainly does. Those
who adapt at greater rates to underfeeding (i.e. reduce their energy expenditure when dieting) will lose less fat in a given calculated "deficit". Therefore, if a coach calculated a 500 calorie deficit, this may not really be a 500 calorie deficit once adaptations have taken place.
With all of this in mind, the concept of a "calorie deficit" needs to be understood in the context of the body's ability to adapt to changes in energy status. Individuals should be treated as individuals, and thus personalised nutrition planning is essential for successful
fat loss.
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Gary McGowan
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