Table of Contents
Do you also hear on the grapevine that a slower metabolism makes it very hard to maintain a slim and attractive figure in your thirties? I’m not even talking about the impossibility of losing weight anymore, it’s all just not true. It’s as if, according to these theories, our imaginary internal energy engine follows a calendar, and by its 30th birthday at the very latest, it went into stand by mode. Such a rapid deceleration then causes uncontrollable gains and going back seems impossible.
But we may also be forgetting the fact that in our twenties we were always out jogging, exercising almost daily, and walking everywhere we could. As we started working, our lifestyles changed almost beyond recognition over the years. Overall, we have become lazy, preferring to sit more than to move, driving everywhere and taking the stairs or going for a run at the most once a week just to feel better. Inexplicable extra kilos we prefer to blame on a slowed metabolism, with a bag of chips and a couple of glasses of wine, we finally give up trying to lose weight while watching “Too Hot to Handle”.
For those who think this way, scientists have come up with an interesting finding. They did a major analysis of the energy expenditure of people of different ages and found that the slowdown in metabolism with the increasing candles on the cake is not as bad as many believe. According to the results of this study, our metabolism reaches its highest rate surprisingly early in life. Unfortunately, this period doesn’t last very long. After reaching its highest rate, metabolism gradually begins to slow down, but then stabilizes for a substantial part of life. In fact, you could say that for more than half of our lives, our metabolism runs at a constant rate on cruise control. The good news is that slowing of the metabolism starts much later than most of us would expect.
So, at what age we have the fastest metabolism, according to the latest study? When, on the other hand, can we legitimately start complaining about a slower metabolism? These are the most important questions we will answer with today’s article. Plus, you’ll learn how to keep a great figure even when you’re not twenty anymore.
Can you have a slowed metabolism? A study conducted by an international team of scientists surprises with ground breaking results
This study was published on August 13, 2021 in the renowned Science journal. Immediately after publication, it began to fill the front pages of other lesser known professional journals. Its results are surprising not only to the general public, but also to the very experts who are dedicated to human biology. Its aim was to map a person’s energy expenditure over the course of a lifetime.
In fact, a number of changes occur during our life, which can affect metabolism in different ways. The researchers wondered, among other things, if there were periods in a person’s life that manifested themselves with increased or decreased energy expenditure. Their main favourite phases included physical development in childhood and puberty, and hormonal changes in women during menopause.
How did scientists track energy expenditure and metabolism rate?
The great thing about all this is that it’s a rare study that has gathered a great deal of data from other scientific papers using a special doubly labelled water technique to determine the energy expenditure. This technique implies that drinking water is marked with a special indicator. This way, the study participants drank the water during the whole day. Depending on how water metabolizes in the body, it is possible to see how much carbon dioxide a person has produced in a day. On this basis, the energy expenditure for the whole day is then calculated. A big advantage of this method is that people undergoing measurements may not need to be connected to devices monitoring gas exchange by breathing all day, as is common in other ways of measuring metabolism. As a result, the participants are not restricted in any way and can basically live as normal. [1-2]
This work also came to the fore because it did not only examine basal metabolism, as was customary in previous studies of similar magnitude. It focused on total energy expenditure. This also includes how many calories a person burns through everyday activities such as walking, playing sports, digesting food or brushing their teeth.
Very little was known about the amount of energy a person burns over the course of a lifetime until the publication of this study. This work can therefore be considered pioneering in its own right. 
How did scientists compare the amount of calories burned in different people?
To compare the energy expenditure of people of different ages and different sexes, scientists needed to find universal narrative solutions. This was obtained in the form of energy expenditure per kilogram of fat-free body weight (FFM). It’s very easily to determine, subtract all the body fat from body weight and you get the result.
The “Fat Free Mass” is made up of muscle mass, bone tissue, organs and other tissues that make up the body. The more Fat Free Mass one has, the more calories one needs for the fat-free mass and the body to function, regenerate and grow.
For example, an adult 30-year-old woman has an average of 50 kg of FFM, burning more energy overall than a 10-year-old child with 20 kg of FFM. However, the difference can be in the amount of calories burned when converted into 1 kg of fat-free mass.
For their analysis, the scientists obtained data from 6421 people from different countries. They included recently born children from eight weeks of age, adult men and women, as well as 95-year-old seniors. This allowed experts to compare how much energy is consumed per day by people across generations and genders during different life stages, such as puberty or pregnancy. 
You might be interested in these products:
4 major findings revealed in the metabolism study. No healthy person has a damaged or slowed metabolism
There were several surprising results from this extensive work. For example, it also revealed the age at which people have the fastest metabolism and, conversely, the period at which metabolism starts to slow down naturally. Thanks to the results of the study, we will learn the difference between the metabolism of a 90-year-old person and a 50-year-old person.
1. People have the fastest metabolism right after birth for the first year of life
We don’t really get to enjoy having the fastest metabolism since we have it right after birth, and at that age we are not thinking about eating more and not gaining weight. However, if a person does not have enough energy during the first few months of their life, the likelihood of growing up to be healthy adult decreases. In fact, according to Professor Speakman, at this age, there is a strong need to satisfy the higher energy demands of the body, which are important for proper development.
In fact, during this period, our body uses a huge amount of energy to develop the brain, bones and other organs. With little energy intake, poor physical development can occur, which could cause a number of health problems in the future. This phenomenon is faced mainly by newborns in poorer countries.
According to the results of the study, the energy requirement of a child under one year of life is roughly double that of an adult on a per kg body weight basis. Unfortunately, what is behind this is not yet known. One of the study’s authors, Herman Pontzer, commented in an interview: “The baby’s cells are more active, but unfortunately, we don’t know exactly what’s going on in them yet. “There is still much to learn about the human body and its evolution.” [1, 4]
2. After the first year of life, our metabolism naturally slows by an average of 3% every year until the age of twenty years
During adolescence, scientists observed an increase in energy output. But this was caused by the natural growth of a person. A larger body simply burns more energy. When converting energy into 1 kg of weight, newborns still have a big head start regarding metabolic rate.
But the experts themselves were surprised by the energy expenditure during puberty, the period from 10 to 15 years. At this time, our body is undergoing a whole series of changes. In a short space of time, boys suddenly have more muscles and generally, their shape changes. Girls typically grow breasts and their first period due to hormones. This is only a small fraction of what happens in our bodies during puberty. Even a complete layperson would assume that during this dynamic period, our bodies burn calories at the rate of a Formula One car. Much to everyone’s surprise, the scientists found nothing of the sort in this study. 
3. From the age of twenty, the metabolism rate remains constant until the age of sixty
This finding is almost shocking to a lot of people. The often-blamed slow or damaged metabolism is thus innocent regarding those extra kilos from Christmas 2016. Not only in our thirties, but also in our forties and fifties. So, where to find the villain who has caused us to no longer dress in a size S, but XL?
Regarding our lifestyle, let’s take a little look into the past. Let’s think about how you lived and spent your free time 5, 10, 15 or 20 years ago.
- How many hours a day did sitting, walking, sports or any other form of movement take up compared to today?
- What about your diet? Do you eat about the same, or do you indulge in more foods that you can describe as unhealthy, but we just can’t help it?
- Is your drinking regimen still the same? Aren’t you drinking sugary or alcoholic beverages more often?
- All of these factors affect how many calories you take in per day, but also how many you burn. Small, and often almost imperceptible, lifestyle changes that lead to a positive energy balance (thus more energy than you burn) are enough. And this simply causes weight gain. 
For a group of participants over the age of twenty, scientists monitored the energy expenditure of pregnant women. They could also be expected to have an accelerated metabolism due to foetal development. However, this has not been confirmed in this case either. While women burned more calories during pregnancy, researchers said this was only due to their overall weight gain.
The old rule that pregnant women should eat for two certainly does not apply. 
4. After sixty, our metabolism naturally slows by 0.7% every year
Even after the age of sixty, the rate of metabolism does not decline as rapidly as we might expect. With each passing year, the slowdown in metabolism is an average of just 0.7%, according to the study. This decrease is mainly due to changes in the human body associated with this period of life. At sixty, we’re typically less active, we lose muscle mass, and our body doesn’t need as many calories to function as it does in our twenties.
Also, mitochondria, the cellular power plants that produce energy, are past their prime. Changes in the amount of hormones circulating in the blood also occur with age. The body typically no longer produces as much growth hormone, insulin, oestrogen or testosterone. All of this can lead to about 26% less energy expenditure after we pass the nineties’ threshold than we did at fifty.
But these changes can be slowed down by lifestyle. This is greatly aided by regular physical activity and a good, healthy diet. When it comes to sports, the ideal combination is a strength training and cardio. These activities promote the maintenance of muscle mass, the proper function of the heart, lungs and also have a beneficial effect on the hormonal system, which is important for overall health. [5-6]
What should you remember from the results of this study?
Just as we experience different life stages, our diet, physical activity and related energy needs change. But the increasing age minimally affect metabolism function. So, the extra kilos you’ve managed to gain over the last year, has nothing to do with the damaged or slowed metabolism or a genetic defect, but rather the change in lifestyle. That’s something to think about before you start complaining about how hard it is to maintain a nice figure in your thirties.
What affects the rate of metabolism?
Our body needs a sufficient amount of energy for maintenance and proper function of all processes that allow us to breathe, think, digest food, walk or even lift weights. The total energy expenditure is thus a bundle of all the calories burned that the body uses in twenty-four hours. [7-9]
5 essential components of metabolism:
- Basal metabolism – the energy our body needs to maintain essential vital functions such as breathing or heart activity during sleep or deep rest. We can simply calculate its value using an online basal metabolism calculator.
- Resting metabolism – the energy required to maintain essential vital functions at rest without additional activities accounts for 60-75% of the expenditure.
- Thermic effect of food – the energy required for digesting food makes up on average 10% of total energy expenditure.
- The thermal effect of normal daily activities, or NEAT, is the energy needed for daily physical activities such as walking to work, preparing food or brushing your teeth, and accounts for an average of 15% of expenditure.
- Thermic effect of activity – energy consumed during deliberate physical activity, such as training, running, cycling, etc., averages 5% of expenditure.
In addition to age, other factors such as body weight and height, amount of muscle mass, genetics, hormonal environment, ambient temperature, as well as diet composition influence the rate of metabolism. Some of these components we can influence ourselves and through changes in lifestyle our metabolism speeds up. If we play more sport and move more during the day, we will simply influence the two basic components of metabolism in our favour. 
If you think you have a slowed metabolism, get it moving by reading our article Can I Have A Slow Or Damaged Metabolism? 5 Tips To Speed Up Your Metabolism.
How do you speed up your metabolism and maintain or lose weight?
One cannot accelerate metabolism by drinking detox juices, taking miracle pills, or running through a meadow barefoot on a full moon. It will be more effective if you start exercising regularly, eat better and get enough rest. You don’t have to make any radical changes from one day to the next, but simply take baby steps to get to a sustainable lifestyle that will lead you to your goal sooner or later.
If you want to lose weight and make things easier for yourself, you shouldn’t miss our article Simple Weight Loss Basics: You’ll Be Surprised What’s Truly Important.
1. Diet for weight loss or weight gain
When losing or gaining weight, a person generally cannot do this without a change in our diet. You’ll probably have to cut back on midnight raids on the pantry that end with a packet of chips eaten, or weekend mode where you literally go off the rails.
It is necessary to reduce energy intake when losing weight and to increase energy intake when gaining it. Calorie counting works well, which can teach you how much cereal to eat for breakfast, meat for lunch or peanut butter with apple for a snack. Following a lightly adjusted diet, try to eat like this for several weeks and then evaluate if it gives you results in the form of changes in body weight and body measurements. Long-term compliance is also crucial. It’s not a diet for a week or a month. In order to maintain results, dietary changes will probably have to be followed for life.
To include the right amount of protein, fat and carbohydrates in your diet when setting caloric intake, read our article How To Calculate Energy and Macronutrient Intake For Weight Loss Or Muscle Gain?
2. More movement during the day
Less exercise throughout the day is an inconspicuous culprit for gaining weight. It is enough to trade the office for a home office, and you lose those walks to and from work. All of this adds up, and even though you’ve kept the weight down so far, you suddenly burn fewer calories than you eat and slowly start gaining weight.
The solution is to stay active, even if you work from home and have a sedentary job. For example, in the morning, walk for coffee or fresh pastries and during the working day, include active breaks to stretch and move the body.
Equally, is it necessary to consider if you really need to go shopping by car, or is a bicycle enough? You can burn some calories on the bike, and do your bit to save the planet. You can also burn calories when cooking, washing dishes or mopping the floor. Housework can increase energy expenditure nicely, so it’s time to finally embrace it. [9,11]
Did you know that you can lose weight just by walking? If you are interested, read our article How To Lose Weight Quickly With Walking?
3. Choose a sport that keeps you entertained and isn’t just a necessary evil
Discovering a sport that will be fun for you, and not just an unpleasant necessity, is like winning the lottery. Not everybody has to run or do CrossFit or go to the gym just because it’s in vogue. It’s about finding a sport that you can stick to for the long term.
Only then will there be long-term sustainable results. If you are a fan of moderately intense activity, fast walking, running, cycling or power yoga will be just great for you. In the case you prefer to work up a sweat with more intense sport, you can try HIIT, group fitness lessons or jump rope.
If you’re wondering how many calories you burn from different sports, read our article How To Lose A Kilogram Of Fat and How Much Energy Is Actually Hidden In It?
4. Exercise and strength workouts
The strength workout is a great tool for maintaining and growing muscle mass. The muscle mass is metabolically more active than, say, fat, and the body uses more energy to preserve it. All you have to do is find the time at least twice a week for some workout with weights, TRX or kettlebell. At the end of any strength workout, you can also experience an accelerated metabolism for another few hours, meaning that your body will be still burning calories. For a higher energy expenditure, a strength workout is the ideal activity. [12-13]
If you’re wondering how to exercise to achieve the most effective muscle gain, you shouldn’t miss our article How Many Reps Should You Do To Lose Weight Or Gain Muscle?
5. Sufficient regeneration and sleep
Sleep and rest are important to regenerate and build strength up for the next day. We’d have a hard time moving on without it. Sleep also affects metabolism through hormone levels, and lack thereof can disrupt the hormonal environment and therefore negatively affect metabolism. This is another reason to get seven to nine hours of quality sleep a day.
You can also support regeneration with massage aids, cold water therapy or stretching. When someone starts something new, they tend to eagerly jump into it at least 200%. Unfortunately, this ends in failure very soon. Therefore, it is important not to burn yourself out at start and not to devote all your time to sport, but to regularly include days off without demanding training and to rest sufficiently.[14-15]
Sleep can affect not only weight loss, but also sports performance and other important aspects of life. If you are more interested in the benefits of sleep, read our article What Happens To Your Body When You Don’t Get Enough Sleep?
What should you remember?
Thanks to a fairly unique study on metabolism, now you already know that age alone has a minimal effect on its rate and calorie burning. By far the biggest role is played by your overall lifestyle, which should include a healthy diet with ample amounts of all nutrients, regular exercise, sport, sleep, rest and a variety of other lifestyle factors. You can reliably influence these factors and use beneficial changes to start losing weight or gaining muscle. You don’t have to give up your efforts to maintain an attractive figure in our early thirties or early forties. And remember, if you take the future into your own hands, you can look great at any age.
Do you know anyone this article could help? Don’t hesitate to share it with your friends.
 Pontzer et al. Daily energy expenditure through the human life course. – https://doi.org/10.1126/science.abe5017
 DLW. – https://doubly-labelled-water-database.iaea.org/about
 Ktori, S. Study Suggests That Yes, Metabolism Does Start to Slow over a Lifespan, but Perhaps Not When We Might Think. – https://www.genengnews.com/news/study-suggests-that-yes-metabolism-does-start-to-slow-over-a-lifetime-but-perhaps-not-when-we-might-think/
 HuffPost UK. This Is The Age When Your Metabolism Actually Tanks. – https://www.huffingtonpost.co.uk/entry/the-age-when-metabolism-declines_uk_61162eaae4b07c1403139ceb
 López-Lluch, G. Mitochondrial activity and dynamics changes regarding metabolism in ageing and obesity. – https://doi.org/10.1016/j.mad.2016.12.005
 Pataky, M. W., Young, W. F., & Nair, K. S. Hormonal and Metabolic Changes of Aging and the Influence of Lifestyle Modifications. – https://doi.org/10.1016/j.mayocp.2020.07.033
 Anthanont, P., Levine, J. A., McCrady-Spitzer, S. K., & Jensen, M. D. – Lack of Seasonal Differences in Basal Metabolic Rate in Humans: A Cross-Sectional Study –– https://www.thieme-connect.de/products/ejournals/abstract/10.1055/s-0042-107793
 Chung, N., Park, M.-Y., Kim, J., Park, H.-Y., Hwang, H., Lee, C.-H., Han, J.-S., So, J., Park, J., & Lim, K. Non-exercise activity thermogenesis (NEAT): A component of total daily energy expenditure. – https://doi.org/10.20463/jenb.2018.0013
 Levine, J. A. Non-exercise activity thermogenesis (NEAT). – https://doi.org/10.1053/beem.2002.0227
 „Slow metabolism" causing weight gain? What really affects metabolism. – https://www.abc.net.au/news/health/2015-11-12/what-really-affects-your-metabolism/6934608
 Peters, H. Keep Up with NEAT: Less Sitting and More Calorie Burning. – https://www.nifs.org/blog/keep-up-with-neat-less-sitting-and-more-little-things-that-burn-calories
 Brellenthin, A. G., Lee, D., Bennie, J. A., Sui, X., & Blair, S. N. Resistance exercise, alone and in combination with aerobic exercise, and obesity in Dallas, Texas, US: A prospective cohort study. – https://doi.org/10.1371/journal.pmed.1003687
 Resistance Training and EPOC. – https://www.unm.edu/~lkravitz/Article%20folder/epoc.html
 Sharma, S., & Kavuru, M. Sleep and Metabolism: An Overview. – https://doi.org/10.1155/2010/270832
 Dupuy, O., Douzi, W., Theurot, D., Bosquet, L., & Dugué, B. An Evidence-Based Approach for Choosing Post-exercise Recovery Techniques to Reduce Markers of Muscle Damage, Soreness, Fatigue, and Inflammation: A Systematic Review With Meta-Analysis. – https://doi.org/10.3389/fphys.2018.00403