Does Yoyo Dieting Damage your Metabolism?

blue tape measure wrapping black medication pill bottle with white cap

This is something I hear often and was the subject of a live training I ran recently with my group coaching programme ‘The Fabulous Butterfly Club’.

People say that if you are constantly on or off a diet you will wreck your metabolism but is this really the case.  And what is metabolism anyway?

Metabolism is the term used to describe the processes by which the body uses energy to support the various systems it needs to survive, such as our digestion, hormonal, growth and repair and respiration among others.   We hear about a fast or slow metabolism, and this is simply the rate at which the body is able to use energy to support those systems previously mentioned.

A person’s metabolism is dictated by a number of individual factors including age, gender, body composition, genetics, health conditions and even the types of food they’ve eaten.  Surprisingly, often when we see someone slim we assume they have a fast metabolism or if someone is overweight we assume it’s down to a slow metabolism.  But, in fact, the smaller a person is the slower their metabolism needs to be since it has less ‘body’ to support and vice versa.

So, does yoyo dieting actually damage your metabolism?  Despite this being a common statement thrown around in the media, it’s not really possible to damage your metabolism.  You can’t break it!  However excessive dieting can certainly cause what’s known as ‘metabolic adaptation’ or ‘metabolic down regulation’.

In simple terms this means that when you commence a diet (ie create a calorie deficit through lowering calories from food) your metabolism will naturally start to adapt to a perceived shortfall in food.  The body is incredibly adept at survival.  It has in-built mechanisms to help it maintain life.  So when it thinks it may be short on food it begins to slow down some of the systems that aren’t immediately essential to life.  For example, it will cause us to move around less to preserve energy.

It makes sense then, that the bigger the deficit we create, the more of a panic our body will perceive, and the more aggressively it will slow the metabolism in an attempt to preserve us from death.

When we crash diet, in effect creating a large and rapid calorie deficit (as is the case with some very low-calorie diets such as meal replacement programmes) we may immediately see some very rapid weight loss (although this will almost certainly not be fat loss which is ultimately what we want when we diet).  But before long our metabolism will have slowed down to accommodate the lack of energy being received, thus causing an inevitable plateau.  When we reach this plateau weight loss will stall.  If, in the case of some very low-calorie diets, you’re only on between 600-1000 calories you’re left with nowhere to go.  You can’t realistically reduce your calories any further, and chances are you don’t have enough energy to create a further deficit through exercise and movement.  Remember chances are your body will have already turned the switch down on moving around too much.

It’s unrealistic to expect that a person could remain on a severe calorie restriction indefinitely, so there will undoubtedly become a point where self-discipline and willpower give way and a blow out ensues.  Binge eating is a common problem when someone has been severely calorie restricted for an extended period of time – coupled with the psychological impact of hitting the plateau, leading to feelings of ‘what’s the point’.

Let’s look at what is likely to happen now that we’ve ‘blown the diet’.  Not mentioning the emotional factors – feelings of failure, guilt, shame among others, physiologically we’re not in a great place either.

We’ve now likely consumed a large number of calories but our body’s systems have all slowed down, so what we could have maybe got away with at the start of the diet we can no longer get away with because we’re not burning calories at the same rate we were before.

Let me try to explain this a bit more clearly.

Our calorie needs are based on our Basal Metabolic Rate – this is the amount of energy we require just to exist.   We then have the energy we require to move about and function day to day.  This is known as NEAT which stands for non-exercise activity thermogenesis.  We then have EAT which is the energy we require on top of BMR and NEAT if we want to play sport or go dancing or workout in the gym.    In very simple terms these factors make up our Total Daily Energy Expenditure (there are other factors such as the thermal effect of different foods but let’s keep things simple for now).

So let’s imagine we have a female who requires 2000 calories per day to carry out her daily activities.  Let’s also assume that her basal metabolic requirements are 1400 calories per day and her NEAT and EAT account for the remaining 600 calories.

She decides she wants to lose weight and believes if she drops her calories to 1000 per day she’ll see fast results.

She is now eating 400 calories less than her body requires just to fuel its basic needs (remember BMR!).  Her metabolism starts to adapt to the lower calorie intake and slows right down to preserve energy.

She sees some great results for the first few weeks then bam, she goes for a couple of weeks without any changes.  She thinks the only thing she can do is to drop her calories further so she starts eating just 800 calories a day.

Again, she sees her weight start to come down but she’s constantly hungry, hangry and feels pretty rubbish.  She’s got no energy, her skin looks sallow, her monthly cycle is erratic and she’s pretty sure her hair is falling out!

Pretty quickly she reaches another plateau as the body frantically tries to adapt further to the lowered energy intake.

We can see that there is no way she can simply keep reducing calories.

Or maybe another scenario is that she reaches her target weight and decides to go back to eating a more ‘normal’ amount of calories.  So being conscious that she doesn’t want to  regain weight and go back to the 2000 calories she used to eat, she ups her calories to 1800.  She’s still eating less than she used to but her weight is going back up, in fact before long she’s not only put back on all the weight she lost, but more than likely a bit more on top.

This is pretty obviously when we realise that her metabolism hasn’t yet caught up with her increased calorie intake.

So what is the solution?  Are diets doomed to fail every time?  Is there any point in trying if they’re never going to work?

Well thankfully it is quite possible to lose weight and keep it off but we do have to be a bit more realistic about the time frame in which it can happen.  Creating a small deficit in energy intake through food, and creating a corresponding deficit through energy output (increased NEAT and EAT) can help to offset metabolic down regulation.

Small, habitual changes will help the body to gradually adapt to the lowering energy needs, as well as avoiding the psychological challenges that severely restricting food choices can create.  Being realistic about how quickly the weight will come off is vital – chances are it didn’t go on in 12 weeks so it’s pretty unlikely it’s going to come off and stay off in 12 weeks.

Choosing whole foods that take more effort for the body to digest will help too.  When we eat highly processed foods much of the work of breaking it down for processing by the body has been done before it even comes out of its plastic wrapper.

Finally incorporating exercise that helps to build muscle tissue, such as resistance training, will also help to maintain a higher metabolism, as well as helping to shape and tone the body and provide essential core balance and coordination – vital as we head into our later years.

So, to summarise, while crash diets won’t break your metabolism they will certainly cause it to slow down to a level which will negatively impact not only our ability to lose the weight we want to lose, but also our quality of life, energy levels and vitality.


Bev Thorogood is a Midlife Transition Coach and Trainer.  A certified nutritionist, personal trainer and health coach specialising in helping women over 40 navigate their way through midlife and beyond.  Using her unique NEST framework she offers a whole mind/body/soul approach to her coaching, finding balance between Nutrition, Exercise, Sleep and Stress, Thoughts and Feelings.

If you’d like help to improve your NEST through ongoing support, education, coaching and the community of a group of midlife women all intent on being the best, healthiest, most vibrant version of themselves come and join The Fabulous Butterfly Club.  Simply click on the purple text below to join.


The Fabulous Butterfly Club is a group coaching programme that provides members with access to an ever growing library of educational resources, recipes, workouts, videos and webinars as well as a private Facebook community for support and accountability.  Included in the monthly subscription is a fortnightly LIVE coaching session with me via an online meeting platform where members can get their individual questions answered.

There is no minimum term contract, no tie and in you can cancel at any time.  What’s more you can try a whole month for free to see if it’s right for you.




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