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Our metabolism 100% slows down when we are in a calorie deficit. It's a real thing.
"Starvation mode" and "damaged metabolism" are not a real thing, but rather terms used by the diet industry & social media influencers to get you to buy in to their product or service.
Although our metabolism does slow down when dieting, it is completely reversible, and its impact can definitely be reduced when you are in a calorie deficit.
Why does our metabolism slow down when dieting?
Long story short, our body doesn't understand that we are in a TEMPORARY calorie deficit to drop some weight. It does initially respond with weight loss, as you're eating less calories while your metabolism is still high.
But within a few weeks, our body realizes that we haven't been eating enough. It wants to do everything in its power to keep us alive, in fear of starvation. So our metabolic rate slows to the amount of calories you have been taking in during your calorie deficit. It meets you where you are.
The following all contribute to metabolic slowdown:
Decreased Basal Metabolic Rate (BMR)
As you lose weight, you have less body mass, meaning you don't need as many calories as before.
Our bodies love homeostasis. The initial response to a calorie deficit is weight loss. But after a period of time, our body lowers its metabolic rate to the amount of calories you're putting in, for survival.
Decreased Thermic Effect of Food (TEF)
This is the amount of calories we burn when digesting the food we eat. It can account for anywhere between 10% - 25% of calories eaten, depending on food quality.
In a calorie deficit, we eat less food. By eating less food, we're not burning as many calories durning digestion.
Decrease Thermic Effect of Activity (TEA)
If you lost some weight, and you're working out the same amount as before, you have less mass to move. Less calories are being burnt for the same amount of work. (Unless you are building muscle mass - it does require more energy, so you can improve your metabolism with resistance training.)
Decreased Non Exercise Activity Thermogenesis (NEAT)
Neat is the daily movement outside of exercise.
As we take in less calories, our body automatically responds with moving less, wanting to stay still not to expend extra calories.
You start fidgeting less, less standing, less moving in general without you even realizing this.
Therefore, we naturally just burn less calories.
Decreased Exercise Activity Thermogenesis (EAT)
You have less mass to move as you lose weight, so you burn less calories doing the same workout.
You have less energy to spend, so workout intensity decreases.
Adaptive Thermogenesis occurs
This is the overall change in our energy expenditure (calories burned) in response to changes in our diet, resulting in metabolic inefficiency.
Reducing The Impact of Adaptive Thermogenesis
Although we cannot prevent adaptive thermogenesis/ metabolic slowdown when we are in a calorie deficit, we can absolutely reduce its impact. By doing so, it can make weight loss a little bit easier, as you keep your metabolism higher for a longer period of time.
So what can we do?
Avoid too big of a calorie deficit!
Keep it above 20% from your maintenance.
Minimize stress
A calorie deficit is already stressful on the body. When you add additional stress (emotional/ physical), it only makes weight loss harder.
Avoid excessive HIIT :)
Although it's a great workout, it is a lot for our body to handle during a calorie deficit. It definitely has its place but during a cut, it's better to focus on strength training, and slower cardio. You don't have to eliminate HIIT workouts, just don't overdo it.
Use refeeds, diet breaks, etc
These help keep our metabolism running high, and slow down adaptive thermogenesis, so you don't plateau as fast.
Avoid dropping carbs too low
First of all, you need carbs as they are full of fiber and nutrients. We want to focus on HIGH QUALITY carbs that increase the thermic effect of food (burning more calories when digesting).
They also have a massive effect leptin, (satiety hormone) which is responsible for adaptive thermogenesis.
Reversing Adaptive Thermogenesis/ Metabolic Slowdown
Metabolic slowdown is not permanent if you take the right steps and get out of your calorie deficit into a new maintenance. The goal is to raise your metabolism and hormone function back up. This should be done after any caloric deficit, or even if you've been under eating for an extended period of time/ yo yo dieting/ going through binge & restrict cycles.
So how do we do this?
Follow all the steps above to reduce the impact of metabolic slowdown while in a cut.
Get OUT of the calorie deficit with a reverse diet.
So what is real, and what is fake news?
Metabolic slowdown is real.
Progress can still be made, which would require more adjustments to your calorie intake.
Adaptive thermogenesis is real.
It's just our body's natural response to a calorie deficit.
Although it cannot be avoided, but it can be reduced and reversed.
"Starvation mode" is not a real thing.
This is what people use to describe when they stop losing weight or hit a plateau because of a large calorie deficit. They think that their body thinks it's starving, and therefore can't lose weight.
To be clear, if you are in a calorie deficit, you will lose weight. If you stop seeing progress, it just means that your metabolism slowed down to your new calorie base.
This does not mean that you should cut calories further. It means that it's time for a reverse, maintenance, and then go back into a cut cycle.
However, our body definitely has a starvation response.
adaptive thermogenesis
decreased NEAT
energy levels are down
cortisol increases
sleep quality decreases
muscle loss increases
appetite increases
leptin decreases (satiety hormone)
ghrelin increases (hunger hormone)
sex hormones decrease
thyroid hormone decreases
strength, performance, and recovery decreases
food awareness increases
Metabolic damage is NOT real.
You can't break or damage your metabolism. Yes, it may take some time to undo the impact of a long term caloric deficit, but it is completely reversible. But that's the thing, many people don't want to take the time to get healthy. They jump on the next diet, or restrict themselves even more in hopes of weight loss.
So even if you've lost a ton of weight, lost weight too fast, got too lean, you're a yo-yo/ crash dieter, or even coming from an eating disorder background, there is no sign of there being some sort of a permanent metabolic damage that persist afterwards.
Moral of the story: if you try to lose weight faster, it will only take longer.
Take your time, adjust your lifestyle, create new habits, and do it the right way.