Metabolic Adaptation
The word “metabolism” gets thrown around a lot. It’s used as a scapegoat for lack of weight loss, weight gain, changes in body composition - a whole slew of things.
And I get it. It’s nice to have an arbitrary thing to point to. But, wrongfully placing blame is doing ourselves a disservice in the grand scheme of things, especially when it leads to us feeling frustrated with our progress.
So let’s clear some things up.
Metabolism
First of all, what the heck even is metabolism?
Metabolism is a fancy word for energy expenditure, or the amount of calories (energy) you burn. This is not a stagnant number each day and it’s not speaking to one specific process in the body that some people are better or worse at. It’s simply the amount of calories you expend within a day, some days will be higher or lower than others based on your movement and the food you eat - totally normal.
There are four parts to energy expenditure - Basal Metabolic Rate, Thermic Effect of Food, Exercise Activity Thermogenesis, and Non-Exercise Activity Thermogenesis.
Basal Metabolic Rate - the amount of calories you burn just at rest.
Thermic Effect of Food - the amount of calories burned in the processing and digesting of the food we eat.
Exercise Activity Thermogenesis - the amount of calories burned from planned or intentional exercise.
Non-Exercise Activity Thermogenesis - the amount of calories burned from all other movement (typing, talking, fidgeting, etc.).
Out of all 4 parts of energy expenditure, NEAT is the most variable day-to-day. It will also be the most adaptive to your calorie intake - if you are in a calorie surplus, your NEAT will increase without much (or any) thought. On the flipside, if you’re in a deficit, your NEAT will decrease.
Metabolic Adaptation
Metabolic Adaptation is basically asking the question “how does your body adapt to the calorie intake you provide it?”
Metabolic adaptation is a really cool survival tactic we have built into our bodies. When we have less access to food, we naturally burn less calories to prevent, well, death.
It might seem like this is an outdated stone age thing, but food security is still something people struggle with and this bodily function is incredible.
The way we see this come into play with weight loss, maintenance, or bulking goals is that when we change the amount of calories we provide our body - we might not see the result we’re expecting.
For instance:
Let’s say I maintain at 2,000 calories per day. I decide I want to lose weight so I drop to 1,800 calories per day. After 2 weeks of consistent tracking, I’m not losing weight. What the heck happened?
A few things could be going on:
Perhaps my calorie expenditure (metabolism) has adapted downward closer to 1,800 calories.
Perhaps a 200 calorie deficit is small and losing at this rate would take longer than two weeks to see scale progress.
I’d venture to say it’s a little bit of both.
If weight loss is my goal, I have to further drop my calories, increase my energy expenditure, give or more time, or a combination of those three.
If it’s been 3-4 weeks and you’re still not seeing movement on the scale… okay yeah it’s time to change something up.
People will experience metabolic adaptation to varying degrees.
In a 1999 study by Levine and colleagues, 16 people were overfed to the point that researchers believed they should have gained about 16 pounds. However, not a single person gained the full 16 pounds. Because of metabolic adaptation and the varying degree to which people experience it, the smallest weight gain was just .79lbs and the largest was 9.3lbs (PMID: 9880251).
This should come as a bit of a relief when it comes to those high calorie days where you feel like you’ve “fallen off the wagon”. We have to eat much more than we likely realize to actually gain body fat, especially in a one-off situation. When we see scale fluctuations after going over our calorie target, it is largely due to stomach content and glycogen. Now, that is not to say you didn’t gain any weight when you were on a 7-day all inclusive cruise with an endless drink package and butler service appetizers, but the occasional indulgent weekend is not derailing your goals as much as you might think… unless it’s an every weekend thing which could absolutely pull you out of a deficit.
It can make weight loss frustrating though. The longer you are in a deficit, the greater impact you might notice from metabolic adaptation. After so many weeks in a cut, you may have to drop calories further to keep going, especially if your step target and general activity is already in a place where you can’t realistically increase it.
Reverse Dieting
Reverse dieting is one of the latest fads in all things fitness and nutrition (in my opinion). Basically, it’s the process of getting out of a deficit incrementally, so you might add 50-100 calories per week to your daily target. The thought here is your metabolism will adapt as you increase your calories. Which is true.
But it also happens on the other side, too. If you spend 8 weeks increasing your energy intake to get out of a deficit, that adaptation will drop once you’re cutting calories again.
This also just simply extends the amount of time you’re in a deficit, which you can hear my thoughts on in the Lowering the Barrier: Reverse Dieting podcast episode 11.
So all the nonsense about “reverse diet so you can lose body fat at a higher calorie target in the future” should be put to rest. Coaches who promote this either A.) don’t know any better or B.) want to sell you a solution that does not exist.
There are two reasons I could see for reverse dieting:
Somebody wants to see how high they can push their maintenance calories. They start with their current maintenance and incrementally increase while watching weight. This would have to be a pretty long-term approach and borderline isn’t worth the micromanagement of calories in my opinion. Instead, just give yourself a +-100 calorie target of your expected maintenance. Or look at weekly average calories instead of daily and give yourself a +-700 target (this allows you flexibility on the weekends!).
Psychologically, somebody is worried about the weight fluctuation when pivoting from fat loss calories to maintenance. A gain of 1-5 lbs could be very reasonable depending on food volume, calorie increase, and glycogen storage. A reverse diet will still result in the same weight gain, just slower. But keep in mind - you’d be spending a hell of a lot more time in a deficit by reverse dieting.
Metabolism As We Age
One of the most common things I hear when metabolism comes up is that weight loss was so much easier in my 20s than it is in my 50s or 60s and that their metabolism has slowed down.
Well, Herman Pontzer in 2021 did a study on metabolism titled Daily Energy Expenditure through the Human Life Course and he found that from the ages of 20-60, we really don’t see a change in metabolism. After age 60 it does start to slow down, but it’s much more gradual than people think - less than 1% per year, adding up to about 7% per decade (PMID: 34385400). For reference, if your maintenance calories at age 60 are 2,000, it could be about 1,860 calories at age 70. That’s a pretty small amount - 2 Oreos a day.
So what’s causing the difference between weight loss/maintenance in your 20s versus your 60s?
Life changed.
You might be more sedentary.
You probably aren’t chasing your kids around anymore.
You might go out to eat more.
You might drink more.
Your body didn’t change as much as your lifestyle did.
Soooo, How Can I Boost My Metabolism?
Well, now that we’ve established that metabolism is related to energy expenditure, this question is much simpler. We need to expend more calories than we consume and we can do that by either eating less or moving more.
Increase your steps. We give this advice A LOT, but it truly is so impactful, not only to your calorie expenditure but general health as well.
Some strategies for increasing steps:
Under desk walking pad/standing desk, if you’re an office worker who can’t change their furniture, you can still use a walking pad at home when you watch TV or read.
Add 5 minutes to your daily walk, if you’re already taking one. Or start going for a daily walk.
Pace around when you’re on a phone call or scrolling social media.
Park farther away from your destination.
These are all simple strategies, but can easily add a few hundred or thousand steps per day.
Eat more protein. Protein has a higher thermic effect than other macros, so we do burn slightly more calories when processing and digesting it. Now it’s not like protein is suddenly “calorie free” or that you burn as many calories as you consume, but it does burn slightly more. Protein is also very satiating which can help prevent you from feeling hungry and be more adherent in your calorie deficit.
Gain more muscle. At rest, muscle burns about 6 calories per pound versus body fat which burns about 2 calories per pound. This is at rest, with decent activity it’s more like 9-10 calories/lb. This isn’t a huge increase in expenditure, but it does add up.
Sleep more. Seems counterintuitive, but the better rested we are the more energy we’ll have the next day to stay active. We also experience better fat loss and muscle growth with more/improved sleep.
Basically, the way we boost our metabolism is to manipulate our energy expenditure through our diet and movement.
Not much of a reader? I’ve got some GREAT news for you! You can listen to me (and Matti) yap about metabolic adaptation on our latest podcast episode of Lowering the Barrier. Plus you’ll get 2 more tips for boosting your metabolism when you tune in. Use the links below to listen on your favorite streaming platform.
