Spoiler alert. Your metabolism doesn’t exist to “burn” calories or fat. Here’s how it actually works and why you can’t “hack” it.
In the nutrition and fitness space, metabolism is often discussed as something that can be manipulated or hacked for “maximum” fat burn. Alternatively, it’s also sometimes referred to as this thing that is “broken” for many of us. Neither of these things are true!
So, let’s have a nuanced, yet fairly basic discussion around how your metabolism actually works and how much or how little control you have here.
The first thing you need to understand is that your metabolism is uniquely yours. This is why no calorie estimator will ever correctly tell you how many calories you “burn” and why you shouldn’t bother getting attached to any numbers that those online calculators or activity trackers spit out. They’re all nonsense!
There’s also HUGE variability both person to person AND within an individual depending on your dieting history, activity level, and more.
Also, your metabolism is NOT broken, but it may be down regulated from restricting calories for long periods of time. I’ll explain this further, but for you to understand this, I’m going to need to #science at you for a minute.
First, WTF is your metabolism?
Metabolism is the chemical processes that occur within a living organism – including humans – in order to MAINTAIN LIFE. This is why your metabolism is so beautifully responsive and adaptable. That fucker is working to keep you alive.
There’s several factors that influence metabolism and many of them are beyond our control.
These factors add up to = your total daily energy expenditure or TDEE.
Here’s the major factors that contribute to metabolic “burn.”
BMR (Basal Metabolic Rate): Calories required to sustain basic life function, including maintaining brain activity, circulation, breath, and cellular reactions (70% TDEE)
NEAT (Non Exercise Activity Thermogenesis): The energy your body uses through the subconscious movement such as fidgeting or shivering and conscious physical activity that isn’t formal exercise, such as cleaning and yard work. (10-15% of TDEE)
TEA (Thermic Effect of Activity): Formal exercise, such as strength training or running. (10-30% of TDEE)
TEF (Thermogenic Effect of Food): The energy required to digest food. (10% of TDEE)
So how do these factors contribute to the variability in how much energy one person might need depending on activity OR how two people of the exact same size and activity level can have very different energy needs?
Take BMR. It’s influenced by how much muscle and fat mass you have, but at least 10% of variability here can be chalked up to genetics.
Then there’s NEAT. Some people naturally have high NEAT – aka that person who can’t sit still. I couldn’t find a reliable stat on this, but I’ve read that NEAT could account for a variability of 800+ calories when comparing two people that are the same size!
How do hormones influence your metabolism?
This is COMPLICATED, but yes, hormones do influence metabolism, but not always directly.
For example, if you don’t get enough sleep, you’ll have an increase in the hormone ghrenlin, which signals hunger and a decrease in the hormone leptin, which signals satiety, which is why you might notice you’re hungrier when you don’t sleep well.
However, note that while this is may be greater influence of “energy in, it’s not slowing down your actual metabolism.
Then there’s the hormones T3 and T4 that are produced by your thyroid gland. They have a more direct effect on metabolism, because of how they influence body temp, regulating the rate at which your body uses calories, heart rate, and more.
You might be thinking, but if someone wants to lose weight, doesn’t this STILL add up to eat less and move more? Not exactly.
Remember what I said about your metabolism being adaptable? This is why you can’t game the system.
If you reduce your calories, your body will respond by reducing your NEAT and you’ll naturally fidget / move less.
If you do tons high intensity exercise, your body may respond by adjusting your hormones to increase hunger signals.
If you start doing tons of steps (aka low grade activity) at some point it’ll have diminishing returns and your body won’t “burn” as much.
This also doesn’t take into account other ways that your body responds to caloric deficits – especially aggressive ones.
For some people, there may be a disruption in sleep, which means you’ll be more hungry.
Also, when you’ve been under eating for a long time, there’s an increase in ghrelin and a decrease in leptin, which means an increase in appetite.
Finally, I’ll add that if your metabolism is down regulated from chronic dieting, the best way to up regulate is to eat at maintenance for an extended period of time. There’s no way around this. Give you body a damn break. It needs it.
This shit is complicated and how much these variables affect you depends on your genetics. Those hunger hormones and adaptations are real.
Does this mean that you can’t lose weight?
If you want to lose weight, this doesn’t mean you can’t, BUT this is why it’s so hard. You’re fighting against evolutionary biology and I didn’t even touch on the profound psychological effects of dieting.
The variables that you can influence are caloric intake, food choices (that may influence satiety), and low grade activity (walking) / exercise.
So yes, you have *some* control, but this is why you are best served appreciating the complexities of biology and genetics. It’s not nearly as straight forward as some people claim and when you throw in the emotional component, this is why it can often be helpful to work with a knowledgable coach who can create some guardrails and help you set realistic expectations and find a way not to tank your system in the process.
I hope that when you look at it through this lens, you can appreciate the complexities of it and why starving the shit out of yourself while exercising to the point of exhaustion in the name of weight loss will always backfire AND why it feels so awful if you do that.
TLDR: It’s fine to consciously influence these factors to change your body composition, but it’s worth doing what you can to work with your body instead of against it.
And it’s also okay (and HEALTHY) to acknowledge when it’s not a good time to try to lose weight OR that it might never be a good time to lose weight.
Body autonomy always my friend. I’m not here to tell you what to want for yourself, BUT I will forever advocate that you honor your physical and mental health above any aesthetic or fitness goal.
P.S. Need a little help navigating the nutrition side of things?
I can help! I work with folks who have a variety of goals including supporting their bodies for all of their activities and the demands of life, better energy + recovery, improving their relationship with food and body image, and yes, in some cases fat loss.
Or click here to book a free 20 minute discovery call to chat and see if I’m the right person to help you. 🙂