The real truth about having a slow metabolism

One of the most common things I hear from people is that they have trouble losing weight because they have a slow metabolism.  They want me to teach them how to speed up their metabolism, and while I can do that, there are a couple of more fundamental questions that need to be asked.

First, do you actually have a slow metabolism?  Most of the people who say they do, actually don’t, and if they do, it’s still not their biggest issue. 

Second, what does having a fast or slow metabolism even mean?  There’s a lot of confusion around this, and as I’ll show you, it actually means three totally different things.

In fact, there are four factors that go into have a “slow metabolism”- three which affect how much energy you burn, and one which simply makes you think you have a slow metabolism, when you really don’t. 

You probably just suck at tracking calories

When people say they have a slow metabolism, that they can’t seem to lose weight even when they eat at a caloric deficit, what’s actually going on, 99% of the time, is they’re eating more than they think, and exercising less than they think.  That’s it- you probably don’t have a genetic disorder or a raisin where your thyroid gland should be.  You’re probably just doing a terrible job of tracking calories.

In fact, studies show that people who have a history of diet resistance (i.e. dieting hasn’t worked for them) and believe their weight problems have a genetic cause typically underestimate calories eaten by about 50%, and overestimate calories burned in exercise by 50% as well.  Here’s what that can look like in practice:

You think you’re eating 1500 calories a day, and burning 3000.  But you’re actually eating 3000 calories a day.  At the same time, you’re only burning 2500- your Basal Metabolic rate of 1800, plus a couple hundred from exercise, plus a few hundred from normal everyday activity.  Important note here: if you’re using a cardio machine that tells you how many calories you’re burning, the number it gives you is too high, as it includes your BMR. 

Even more important note: those numbers show you exactly why diet is more important than exercise in determining calorie balance.  The food you eat accounts for all of the “calories in” side of your calorie balance, but exercise only accounts for a fraction of “calories out.” 

I work out for 30-60 minutes, 6 days a week.  My daily caloric expenditure is around 2700-3000 calories, but about 1800 of that is my BMR, and when you add in a few hundred calories burned walking around, surfing, and punching the wall every time someone tells me they can’t lose weight because they have bad genetics, even my extreme workouts don’t account for that many calories.  There’s simply no way around having to eat less.

So having said that, let’s look at those other two factors- BMR and calories burned just living your life.  There are two big factors that can affect BMR, and one that affects how much you move around. 

Thyroid metabolism- your body’s furnace

When people talk about having a fast or slow metabolism, this is usually what they’re talking about- the idea that some people’s bodies burn more calories than others, even controlling for body weight and activity level.  Which they do- just not very much.

In fact, most people’s metabolic rates fall within about 5-8% of average, and pretty much everyone falls within 10-16% of average.  To quote (and I suggest you read that whole article by the way):

One study[1] noted that one standard deviation of variance for resting metabolic rate (how many calories are burnt by living) was 5-8%; meaning 1 standard deviation of the population (68%) was within 6-8% of the average metabolic rate. Extending this, 2 standard deviations of the population (96%) was within 10-16% of the population average.[1]

Extending this into practical terms and assuming an average expenditure of 2000kcal a day, 68% of the population falls into the range of 1840-2160kcal daily while 96% of the population is in the range of 1680-2320kcal daily. Comparing somebody at or below the 5th percentile with somebody at or above the 95th percentile would yield a difference of possibly 600kcal daily, and the chance of this occurring (comparing the self to a friend) is 0.50%, assuming two completely random persons.

Got that?  Two thirds of you fall within three hundred calories of each other, and everyone who doesn’t have a clear, diagnosed metabolic disorder (fast or slow) falls within 600 of each other.  Another thought- one third of the population is obese, which means at least half of obese people fall within one standard deviation of average.  And more than two thirds of the population is overweight, meaning many overweight people actually have faster than average metabolisms.

Okay, you say, but what about extreme outliers?  What about that final 5% who are more than two standard deviations from the average.  Well, they can’t be too far beyond two standard deviations, because if they were, they’d die.  Remember, your “metabolism” is another way of saying “your body doing stuff to maintain itself.”  Your metabolism can only slow down so much before your body isn’t doing enough to keep itself running, and then it becomes a dead body.

And on the flip side, your metabolism can’t get all that much faster, either.  The energy your body uses can’t just disappear; it has to go somewhere, and that mostly means it gets turned into heat.  And that means your body can’t speed up too much without cooking itself.  So add these two limitations together, and people’s metabolisms probably can’t get much more than 20% higher or lower than average (and again, are usually within 5%). 

You might also be wondering- since bigger bodies inherently conserve heat better, doesn’t that mean bigger people will have slower metabolisms?  Well yes, actually.  In fact, this is a well-established biological rule- bigger animals have slower metabolisms.  However, the variance between humans isn’t huge- bigger people usually have slightly slower metabolisms, but they also tend to just run hotter.  That’s why fat people sweat more- their metabolisms aren’t slow enough to counteract the inherent tendency for a larger body to conserve heat. 

Having said all that, yes, this little difference can still account for two or three hundred calories a day.  All other things being equal (which they almost never are), this can account for one or two pounds of fat gained or lost a month.  But in the long run, a slow metabolism typically only accounts for 10-15 pounds of excess weight before your body reaches an equilibrium point.

So how can you speed up your thyroid metabolism?  A few things.  First, get plenty of sleep.  Second, eat healthy, and in particular get plenty of iodine, B vitamins and other trace minerals, which your thyroid needs to produce thyroid hormone.  Third, lose weight so that your metabolism can speed up without cooking you.  And finally, an occasional cheat day– or better yet, feast/fast– can help, but only if you’re eating at a substantial caloric deficit. 

Body composition, or why you’re probably also miscalculating your BMR 

The other factor that determines your Basal Metabolic Rate is how much muscle you have.    Muscle tissue burns about 7-10 calories a day to maintain itself, while fat burns 2-3 calories a day.  In other words, muscle burns 3-5 times as much energy as fat.  And that means your body fat percentage is pretty damned important.  Incidentally, this is also why men burn more calories than similarly-sized women- we’re simply leaner. 

Most people underestimate their body fat percentage, and that’s a huge problem.  In my experience, people typically underestimate by five to ten percent, and that means they overestimate BMR by 100-300 calories a day. 

So how should you measure body fat?  First off, avoid those bioeletrical impedance scales- they’re worthless, and easily thrown off by your level of hydration.  The best methods are high-tech, like bod pod, hydrostatic weighing, or my personal favorite, DEXA. For more accessible options that don’t cost money, get measured with calipers at your gym, or use a body circumference formula like this one.

So, gain muscle to burn more energy, right?  Yes, but it’s not that easy.  First off, if you’re overweight, you should focus on losing fat first- if you try to bulk when you’re overweight, you’ll probably just gain more fat due to impaired insulin sensitivity.  Get lean first, then bulk. 

You can gain a little bit of muscle while cutting though.  Not much, but a little.  More importantly, you need to not lose muscle.  That means don’t do any starvation diets, and it also means you need to lift weights a few times a week.  And to feed your muscles, you should have a healthy, high-carb meal after each weight training session, even if you’re otherwise cutting carbs.  That doesn’t mean pizza and soda if you’re not super lean already, but it can mean rice or potatoes. 

Finally, remember that because fat also burns calories to maintain itself, your BMR will in fact go down as you lose weight.  And that mens you need to a) keep your diet tight, b) keep lifting weights so any gradual weight re-gain will tend to be muscle rather than fat, and c) do everything in your power to maximize the other two components of metabolism.    

Non-exercise activity thermogenesis, a.k.a. moving around a lot

Whereas thyroid levels and body composition determine your BMR, non-exercise activity thermogenesis, along with your overall lifestyle, determine the other factor that goes into how many calories you burn- your daily activity, outside of “working out.” 

NEAT is all the little stuff you do throughout the day, from walking around, to fidgeting, to taking the stairs instead of the elevator.  For all but the most hardcore fitness junkies, NEAT adds up to more calories burned than exercise does- after all, you’re doing it all day long, even if it’s not as intense. 

When people say that their metabolism has slowed down as they’ve gotten older, what that usually means is that, as they’ve aged, their energy level has declines- and NEAT has gone down with it.  Importantly, NEAT is not about making deliberate choices to burn calories.  Think less “taking the stairs because it’s good for you” and more “going for a walk because you have so much energy you just can’t stay still.”  It’s the sum total of a thousand tiny, unconscious decisions you make all day long.   

Think- when you were a kid, weren’t you always running around, screaming and climbing things like a crack-addicted monkey?  That burns calories, even if it’s not “exercise.”  In fact, one of the reasons I’ve managed to stay so lean is that I’ve never really grown out of the crack-addicted monkey phase.  I still fidget all the time, I can’t write more than three paragraphs without getting up and pacing, and sometimes I have to do a short bodyweight workout just to release all the excess energy I have.  It’s hard to get fat when you’re always moving. 

So to maximize non-exercise activity thermogenesis, you need to have a lot of energy.  If you have the energy, it’ll just happen. 

The number one thing you can do to have more energy is to sleep better.  Keep your bedroom dark, and always make it a priority to get 7-9 hours of sleep a night. 

Second, eat food that energizes you.  That means test different meals, and monitor your energy level afterward.  Eat food that keeps you perked up for several hours after, not food that makes you crash an hour later. 

Also, stay hydrated, and follow a morning routine designed to maximize your mental and physical energy.

Your energy level is one of the biggest, most under-recognized factors that determine what kind of body type you end up having.  Have a lot of energy plus don’t eat much, and you’ll be skinny.  Have a lot of energy and eat a lot, and you’ll get buff.  Have low energy and don’t eat much, and you’ll be skinny-fat.  Have low energy and eat too much, and you’ll be just plain fat. 

That’s one of the reasons I created Bursting with Energy, my premium course that teaches people how to have the energy of a teenager again.  In addition to all the other benefits of a high energy level- mood, productivity, and being able to generally do more with your life and have more fun- a high energy level is one of the biggest things that will cause you to get leaner.  You’ll move more, work out harder, and even build more muscle, all automatically.  Bursting with Energy isn’t on sale right now, but if you join my free mailing list, you’ll be the first to know when it is.

To recap, if you want to have a fast metabolism, you need to do four things.  First, track calories properly so you can accurately judge whether your metabolism is even the issue.  Second, nourish your body so it produces more thyroid hormone.  Third, build a little muscle, even as you lose fight.  And finally, prioritize keeping your energy levels up. 

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