Skip to main content

19 Aug, 2020

Busting Metabolism Myths with Phoebe Liebling


Firstly, can you outline exactly what is the metabolism?

To put it very simply our metabolism is the collection of chemical processes that occur continuously within the body to keep us alive. You will hear a number of different mechanisms being referred to as ‘metabolic processes’ or components of our metabolism and these will be divided into 2 main categories - catabolic processes and anabolic processes. Catabolism is the breakdown of molecules such as glucose and fatty acids to obtain energy, and anabolism is the synthesis or making of compounds needed by your cells.

From the above you would be perfectly right in assuming our metabolism is all about what we’re putting in, and yes that’s a critical element, but we also need to include the removal of waste within our definition. Just as integral to our survival and therefore our metabolism is the action of organs such as the liver and kidneys which take the products of all of these reactions, chop them up and remove them from the body. Without this vital component we would quickly cease to be able to function due to toxicity.

Does your metabolism slow as you age?

Most things do sadly. I refer to ageing as a progressive loss of efficiency, which makes perfect sense if we liken the body to an exceptional piece of engineering (which it basically is) that has been working away tirelessly for you for many years, after a while it’ll start to develop little faults. But just as with a wonderful vintage car, or that food processor that you’ve had for longer than you can remember, a little extra care and attention will keep that fabulous machine speeding along without issue.

When we translate this over to us as opposed to an actual machine that would be looking at things such as an antioxidant rich anti-inflammatory diet, supporting stomach acid (this naturally lowers as we get older and is vital for nutrient absorption) and targeted forms of exercise to preserve muscle mass. Those are the key bits that will be declining so if we jump in and prevent them from dropping off, we halt the efficacy loss and thus have solved the concern before it got started.

So yes, your metabolism can slow but you needn’t let it.

Can exercise boost your metabolism?

Absolutely if used correctly, and I am keen to define this from the outset as not all exercise is created equal. There are a couple of key differences; the influence on energy output in the immediacy, and then the longevity of those effects after the exercise has ceased.

One of the things I encounter frequently is the misconception that cardiovascular exercise is the be all and end all when it comes to being fit and lean. This is unfortunately not the case. Yes, it is a valuable tool to add into your routine, it works the lungs, the heart, supports detoxification through sweating and will make you metabolically efficient whilst you are performing that activity (i.e. you use a significant amount of energy). But the other thing that occurs when you train in this way is you produce adrenaline and cortisol (your stress hormones) and oxidative species (AKA free radicals). These elements, if present continuously in the body, actually lessen our ability to be metabolically effective, and if someone is chronically over cardio exercising they will often find they have an adrenal crash a few hours later meaning they suddenly drop in energy and will overeat for their needs to try and bring themselves back up again. This then impacts blood glucose and insulin levels which is not helpful. Oh, and you can also end up with progressive strain on the thyroid which is another integral influencer on metabolic rate. So yes, intense cardio exercise is useful, but I would never suggest it be more than 25% of someone’s training schedule.

The other side to the coin is the relative proportions of the different types of body mass we have, AKA our fat to lean muscle mass ratio. Lean muscle is metabolically active even at rest, so the more we have the faster our resting metabolic rate will be.

This is why when we are looking at increasing our metabolism with exercise, we want to make sure we are incorporating forms of physical activity that encourage the development of more lean muscle mass. This is where the drive to add more weighted training comes in, you will use energy whilst performing those activities (your snazzy fitness tracker might indicate less than if you had gone spinning for an hour) but the big difference is that through working your musculature in this way you then end up with a more preferential muscle:fat mass balance, and that will mean that after you finish your session you continue to use energy at an increased rate. Now aesthetics are not the most important thing by any means but feeling comfortable in your appearance is a great driver to continue to look after ourselves which is another benefit to resistance style training. That lean muscle mass is much smaller in volume than fat mass so swapping to options such as reformer pilates, weightlifting, strength circuits and bodyweight/calisthenics over pounding the pavements 5 times a week will not only positively influence your metabolic rate but also beneficially influence body shape too. Don’t confuse this with an encouragement to start tracking progress on the scales however as the classic ‘muscle weighs more than fat’ is true, if you do want to keep tabs on how your efforts are working then use items of clothing or a soft tape measure to compare every 12-14 days.

Is it true that crash dieting can actually slow down your metabolism?

Yes! This is to say that unhealthful approaches to weight loss, those that force the body into a prolonged stressed state, will negatively impact our natural body mass balancing mechanisms. If someone were to follow a well-managed regime that helped them to lose weight progressively over time then that wouldn’t have the same effects.

Our body works on a number of ‘set points’ which it determines based on its previous experiences. You have your normal, resting state (AKA parasympathetic nervous system dominant) points which is where you will sit with things like your pulse, blood pressure and breathing rate on any given day, and then you have your sympathetic nervous system dominant (AKA fight or flight response/stressed state) situation which will alter these. Instead of having to adjust each time you swap between the two imagine your body has marks on a wall - when it needs to quickly switch because it thinks there’s a threat to your survival (which is what our sympathetic nervous response is there to do) it just jumps to that new mark as opposed to climbing a ladder rung by rung.

The link between the above and how dieting influences your metabolism refers mainly to how and how much additional energy we hold as fat, and consequently the ease with which we can burn it off. Yo-yo dieting is seen as a form of threat because you are depriving the body of energy in a sudden way, and your brain is just a control centre in a black box, it can’t tell that the danger signal you have created is because you’ve decided you need to quickly drop X number of pounds at speed, so it says to your body that it should hold on to extra energy stores (usually around our middles as it’s easier to access if it’s in one place) because we are living in a time with uncertain food supply. This would also link with an incremental slowing of the energy we use overall in an attempt to preserve what we have for longer.

This is why those who diet in this way will progressively find it more difficult to lose weight over time, their body has taken their set points up the wall so they will hold more fat as a baseline, and plus when they return to eating in a more normal pattern they then find they put on more weight as their body is in storage mode using up the fuel they put in at a slower pace. This is something well documented in clinical studies and in fact those who had never dieted always come out as the leaner group when compared to yo-yo dieters.

For those that struggle with carrying excess weight, and vice versa, does metabolic rate play a part?

At a very basic level it would stand to reason that someone of a leaner body composition is utilising energy more efficiently than a larger individual, but at the same point that doesn’t mean they are healthier as many ‘slim’ people can have high amounts of visceral fat around their internal organs (more problematic in terms of their health) with little subcutaneous fat, plus this statement also doesn’t examine why there would be metabolic differences. I must also mention here that we are all naturally genetically unique and body type/shape will vary from person to person as a result. Modifiable factors such as intestinal bacteria numbers and diversity will also vastly influence our metabolism and can be a significant player here.

My approach to this concept is always from a health directed perspective, first and foremost you address your overall wellbeing and that in turn will allow your metabolism to shift to a higher rate of efficiency. As I say above our body is a fine tuned machine and it doesn’t want to be inefficient, so if we support it to function optimally it will naturally move towards this as a preference.

If someone is looking to lose weight, are there actually ways to significantly change their resting metabolic rate? Or should they instead focus on longer-term strategies for a more effective approach to altering body weight?

So, my answer here is that yes you can change your resting metabolic rate to aid weight loss, but this is not an overnight switch. Progressive, incremental changes over time are always preferential, and these will also then be long lasting. Anything that happens super quickly is likely to reverse just as swiftly, and true fat loss will not occur in a matter of days as your body cannot remove those cells that quickly. Numerical weight loss in such a short time frame is always going to be predominantly through water loss.

My top tips are:

  1. Firstly, to address stress and sleep levels, if these aren’t good, they hold the body in a state of stasis and then you’re fighting an uphill battle.
  2. Next look at the forms of exercise, these could actually be contributing to those perturbed stress/sleep cycles and switching to calmer forms of activity, the strength style training I mention above, and restorative movement such as yoga will be an incredibly positive influence on your metabolism.
  3. Then of course consider your dietary choices, but again if we are well rested and calm, we will always pick better things. We can all stand to drink more water, ditch/at least halve our consumption of stimulants, turn to savoury over sweet snack options and avoid processed foods. Those simple tweaks are always a great place to start along with making sure you’re actually eating enough! I can’t tell you the amount of times I have been presented with a food diary and wondered how the person in front of me is not about to devour the cushions on my office sofa. Without adequate fuel your body cannot work properly (and you’ll induce that yo-yo dieting-esque panic state I describe) so choose well, have proper meals and avoid eating late at night as that extra energy has nowhere to go except storage, plus if your body is digesting when it should be resting you won’t get the most out of that all-important night’s sleep!


Phoebe Liebling is a London based Nutritional Therapist and award winning product and recipe developer. She splits her time between seeing clients for clinical consultations and her work as a consultant which can have her doing anything from formulating therapeutic supplements and training other practitioners, to getting into the kitchen and creating wonderfully delicious and nutritious things. A running theme through everything Phoebe does is a passion to empower others to understand how dietary and lifestyle choices impact our health and wellbeing, and to show that eating in a health minded way does not mean sacrificing on flavour or enjoyment! More information on her clinical services can be found on her website, and you can find endless foodie inspiration with that added educational spin to it on her Instagram feed as @_naturalnourishment.