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KEY POINTS:
- Increasing one's metabolism is often marketed as a quick and easy way to make fat loss easier.
- Unfortunately, there are no quick and easy ways to increase our metabolism. It requires time and significant amount of effort, and even then it's unlikely to be as much as you'd think.
- The sooner we can accept that we're unlikely to ever get to a point where we can eat a lot more food and lose fat effortlessly, the better off we'll be, as this will allow us to focus on realistic and sustainable methods.
In my opinion, ones "metabolism" or "metabolic rate" is an enigma to the majority of individuals.
A buzzword that's thrown around by PT's and "health coaches" to promote a specific workout style, diet or pill they're pushing.
Or as the sole reason why one isn't losing weight. Because they have a "slow metabolism".
Advertisers and marketers are also well aware of this buzzword. Thus we've seen the rise in supplements, foods, exercises, diets and strategies to "boost" one's metabolism.
Add to this the frequent messages on Facebook and Instagram, that our favourite #fitspo stars are shredded on over 3,000 calories per day, and we can start to see why the promise of increasing one's metabolism is so enticing.
It's the holy grail. Looking better while eating more food!
But is there any truth to the claims? Can we significantly increase our "metabolism"? And if so, how?
First of all, we need to get a few things clear. Like what we're referring to when we talk about our metabolism.
Technically, our metabolism can be defined as the sum of all the chemical processes in the body that keep us alive. For this article and to simplify things a bit we can also refer to our metabolism as our Total Daily Energy Expenditure or TDEE. This is (as the name suggests) the total amount of energy your body expends in a day. Or how many calories you burn.
We can then further break down our metabolic rate or TDEE into four key components.
1) Resting Metabolic Rate
Our resting metabolic rate (RMR) is the energy our body uses to survive. As you sit reading my nerd gibberish, thousands of cellular reactions are happening within your body. Your brain is using glucose for fuel; your heart is beating, protein in your muscles is being broken down and synthesised. These are just a few of the many continuous processes within the body that all use energy.
Lean body mass (muscle, bone, organs, your brain etc.) is a significant determinant of RMR, with gender, age and height also playing roles. In general, RMR makes up anywhere from 50-70% of our TDEE depending on how often we leave pull ourselves away from Netflix and venture outside or to the gym.[1]
It's within RMR that the “slow” or “fast” metabolism argument lies. We’ve all had a friend with a "slow metabolism" who is often quoted saying something along the lines of "all I have to do is look at cheesecake, and I gain weight!".
We also all know someone who seems to exist on a diet full of energy dense "junk" without gaining a gram of fat.
Contrary to popular belief RMR doesn't vary as much as one might think. Yes, there are the genetic outliers, but 96% of people fall within 16% of the average RMR.[2] That's roughly 200-300 kcal or 3 Tbsp of peanut butter, or a couple of those natural, refined sugar-free bliss balls you love.
RMR is also a poor predictor of future weight gain.[3] So even if you DO have a low RMR, the data would suggest that this doesn't mean you're destined to gain weight.
2) Thermic Effect of Food (TEF)
The thermic effect of food (TEF) refers to the energy used by the body to break down, digest, absorb and use or store certain nutrients. The amount of expenditure TEF contributes to metabolic rate will vary depending on the nutrient breakdown of the diet. More on that later.
3) Thermic effect of Activity (TEA):
The TEA accounts for the energy you burn with formal, conscious exercise. When you go to the gym, go for a run, or hike up a hill, these all fit into the category of TEA. This can vary drastically between individuals based on their LBM and the type, duration, frequency and intensity of their exercise.
4) Non-Exercise Activity Thermogenesis (NEAT):
Also known as Spontaneous Physical Activity (SPA), this accounts for all the movement not covered above. Getting up from the couch and walking to the fridge? That's NEAT. Doing chores around the house? NEAT as well. Even small movements considered fidgeting and postural type movements fall under this category.
Now that we understand what makes up our metabolism we can start to address how we could potentially go about increasing it.
To my knowledge, there is currently no research to suggest that an individuals metabolism will increase magically outside of one of these aspects of TDEE. That’s to say that to increase one's metabolism, we would need to raise it via one of the above components.
So with this knowledge, the question then becomes how can we potentially increase metabolic rate and by how much?
Once again we're going to break this down into each respective component of TDEE.
1) RMR
As mentioned earlier, lean body mass comprises a large part of our RMR. So, adding some beefy slabs of muscle to your frame will increase your metabolic rate.
BUT, It's probably a lot less than you think.
We're talking 13 calories per kilogram of muscle per day at rest. [4]
So, if you bust your ass in the gym (which will increase your metabolism acutely) and gain 5 -10 kilograms of muscle, you'll be rewarded with a potential increase of 65-130 kcal/day. Now hopefully you’re not sitting around resting all day, with the increase in muscle mass your fat mass may increase a little too, plus a larger body expends more energy doing the same tasks, so let's round it up to 200 calories a day. We'll take it, but don’t expect to be able to sit back with your feet up while your increased muscle chews through calories.
Other than increasing lean body mass there isn't much a HEALTHY individual can do to improve their RMR. It's more a case of avoiding situations that might lead to a decrease.
For example, avoiding nutrient deficiencies, which may over time lead to a reduced metabolic rate, is relatively manageable by focusing on eating a varied, nutrient dense diet.
Dieting to reduce our body fat results in a reduction to our RMR due to lowered bodyweight, reduced thyroid hormone, leptin, testosterone, and increased efficiency of the energy creating process within our cells. [5] So avoiding prolonged periods of time at body fat levels far below your comfortable range, and potentially breaking up periods of dieting with maintenance calorie "breaks" will help to ensure your metabolism remains "stoked". [5,6]
Damn our amazingly adaptive bodies for evolving with mechanisms to reduce the likelihood of us starving to death!
Potential Metabolic Increase: Meh ~ 100-300 kcal.
Effort: High.
2) TEF
Eating more food, in general, will typically result in more energy expended through TEF. Makes sense. [7]
So what about the food we eat? Perhaps a certain diet results in us expending more energy without trying?
No, it's not keto. [8] In fact, fats themselves are the easiest macronutrient to store. Only 3-5% of the energy of fats is required to store them in the body, compared to 8-10% of the energy of carbs and, spoiler alert, 20-30% of the energy of protein.[7] That's where part of ketogenic diets potential benefits lie. They typically lead to individuals consuming more protein.[8,9] High protein diets have been shown to result in increased diet-induced thermogenesis, meaning the body works hard for its money.[7]
There's one other factor that falls within this category. The level of processing food goes through. There's evidence to suggest that consuming whole foods requires more energy to digest than more processed foods.[10,11]
Potential Increase: Meh.
Effort: Minimal
3) TEA
So far the potential for us to increase our metabolic rate has been underwhelming.
But what about the big dogs.
If we can't rely on non-exercise or movement related components of our metabolism to make us the human torch, then surely we can exercise our way to improved body composition?
This appears true. To an extent.
Doing more exercise, whether that's aerobic, resistance or a combination of the two is going to increase your overall energy expenditure IF other factors are held constant.
So yes, we can increase our metabolic rate by moving more (who'd have thought).
But there appear to be issues with this as well.
Firstly, the majority of adults I know don't have an abundance of free time that they can dedicate to training. It's hard enough getting to the gym 3-4 times a week for an hour. Asking them to commit to much more is often pushing it.
Secondly, some studies have shown many individuals tend to compensate for the increased energy expenditure of increased training.[12] This is illustrated in studies showing less than predicted weight loss for a given amount of energy expended through exercise. [12,13]
So while we may add three high intensity sessions a week expecting to see the fat melt off, it appears that many individuals will compensate for this increase in energy expenditure by subconsciously reducing NEAT levels [12] or increasing energy consumption.
What's interesting is that there may be mechanisms within the body that constrains our overall energy expenditure over time. [14] Such that while initially increasing exercise substantially would increase our metabolism, if continued over time, the body would make adjustments to reduce its expenditure to maintain it's status quo.
Potential Increase: Massive...at least acutely.
Effort: High.
4) NEAT
Finally, we have NEAT.
For sedentary individuals, it may only make up 10-15 % of their TDEE while for those who are moving a lot more, it can make up close to 40-50%. [15]
What this illustrates, however, is of all the components of TDEE, NEAT levels may have the greatest potential for a long-term increase, depending on baseline levels. [16]
In a fascinating study, Levine and colleagues [17] found large differences in the amount of weight gained by individuals placed on a 1000 calorie surplus for eight weeks. The range of weight gain varied from 1.4 kilograms to 7.2 kilograms! When they examined the potential causes of difference between those who gained the least and most amount of weight they found it was changes in NEAT levels and that they directly predicted fat gains.
Unfortunately, changing one's NEAT levels isn't easy, as it appears that they are profoundly influenced by:
- Our genetics.
- Our environment.
- And our occupation. Calories burnt through NEAT can vary by as much as 2,000 between individuals of similar age, lean body mass and gender based on their jobs! [17]
So, while NEAT does have the potential to increase our metabolism to a significant degree, it also appears that to do this intentionally and consistently over time requires a considerable amount of self-discipline or lifestyle change.
For example, all those ideas we usually scoff at like parking further from your destination, taking the stairs, going for a walk around the office once an hour, standing rather than sitting, riding to work rather than driving etc. all add up.[18] In fact, those small things could be the difference between you maintaining a lower body fat at a higher intake.
Potential increase: Moderate
Effort: Moderate
So if there's no easy way to increase my metabolism magically, what should I do?
Do as much as is realistically reasonable for your goal and life. Anything more than this seems to require too much self-discipline and resources to be sustainable.
Based on the above breakdown we can isolate a number of ways that we can increase our metabolism. They may not be as sexy, marketable or easy as eating specific foods, taking a pill or following a specific diet, but they do have evidence to suggest that they work, which is a more than we can say for the former.
1) Train to build muscle.
It doesn't have to be your primary goal but you should aim to increase or at least maintain your current level of muscle mass. Not only will this mean you'll be expending more energy training and recovering from resistance exercise, but over time you'll get the added benefit of burning, albeit small, more calories at rest.
2) Avoid spending long periods of time in severe deficits or at a body fat much below your bodies settling range.
Undereating and reduced levels of body fat (from YOUR norm) both independently reduce your metabolism via reductions in RMR and TEF. You're also a lot less likely to be building muscle in this state.
3) Eat a nutrient dense, varied diet.
Pretty straightforward. We're looking to ensure that we aren't deficient in any nutrients. Vitamins, minerals, phytonutrients etc. are all vital for an optimal functioning body, including one's metabolism.
4) Consume a high protein diet.
Aim to consume between 1.6-2.4 grams of protein per kilogram of body mass. Aim for the higher end of this range when dieting to help prevent any muscle loss as body fat decreases.
5) Eat mainly, minimally processed foods.
The increased diet-induced thermogenesis (DIT) from eating whole foods over processed foods is probably the smallest on a long list of benefits. Without writing another novel, eating mainly minimally processed foods helps us avoid nutrient deficiencies, eat adequate amounts of fibre and makes it easier for us to regulate our energy intake.
6) Find your exercise 'sweet spot'.
By 'sweet spot' I'm referring to the amount of exercise you can realistically, consistently do, without seeing behavioural adaptions. For most of us, we seem to be able to increase our energy output through exercise to a certain point before the body starts to compensate. While this "point" can be hard to recognise, if you find your training volume is leaving you lethargic, tired and on the couch more, then it may be time to pull back a touch.
7) Find easy ways to increase your NEAT.
- Grab a Fitbit/activity tracker and making sure you hit 10,000 steps per day.
- Get into the habit of going for a morning walk.
- Park further away from your destination.
- Utilise a sit-stand desk or even better a treadmill desk.
- Make catch-ups with friends active by grabbing a coffee and walking.
- Taking the stairs.
At the end of the day, we need to accept that we're unlikely to see major changes to our metabolic rate without putting in considerable time and effort. The sooner we can accept this, the sooner we can start to construct a diet and lifestyle that takes our personal needs and goals into account.
References:
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3.Weinsier RL, Nelson KM, Hensrud DD, Darnell BE, Hunter GR, Schutz Y. Metabolic predictors of obesity. Contribution of resting energy expenditure, thermic effect of food, and fuel utilization to four-year weight gain of post-obese and never-obese women. The Journal of clinical investigation. 1995 Mar 1;95(3):980-5.
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