Metabolism and you: huge new study may shake your weight loss theories to the core

Decades-long metabolism research offers new insights into how metabolism changes as we age

how to lose weight
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Can you speed up metabolism for quicker weight loss results? This has been on the mind of many dieters in recent years, decades even, especially ever since the media started writing about the 'obesity epidemic'. We were told that metabolism gradually slows down as we age and our weight gain through our 30s and 40s is a result of the ageing process. A recently published research paper published in Science might put all these 'facts' and more to rest.

As reported by The New York Times, the research paper is called "Daily energy expenditure through the human life course" and although it's only been published recently, the study is the result of decades-long research that involved numerous universities and contributors. As a matter of fact, the paper has more than 80 co-authors listed.

“This new research is certainly groundbreaking and poses many new questions", says Olga Hamilton, Head of Nutrigenetic Science at NGX (Nutri-Genetix), "Hopefully, future research can answer all these questions and help with the fight against obesity.”

The paper, probably unintentionally, debunks a range of metabolism facts, including the rate of decline as we age the difference between energy expenditure of sexes. Of course, there are many research papers that tried to debunk similar metabolism-related facts before, but what makes this particular research credible is its scale: over 6,400 people were observed from ages 8 days to 95 years using what's called the "doubly labelled water method".

What's the doubly labelled water method?

As explained by the Cambridge Biomedical Research Centre, "The doubly labelled water (DLW) technique measures total carbon dioxide production by observing the differential rates of elimination of a bolus dose of the stable isotope tracers, 2^H (deuterium) and 18^O. Combined with an estimate of the respiratory quotient, this yields an estimate of total energy expenditure."

The doubly labelled water method is currently the gold standard for assessing total energy expenditure in "free-living" individuals. Its precision has been confirmed by other studies too.

new metabolism study: plates full of healthy food

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The beginning of a new era

Thanks to the researchers' cooperation through the decades, the research shone a light on the metabolic differences of people, or more like, the lack thereof: as it turns out, you won't be able to blame a slow metabolism for your weight gain anymore.

The paper states that "energy expenditure (adjusted for weight) in neonates was like that of adults but increased substantially in the first year of life. It then gradually declined until young individuals reached adult characteristics, which were maintained from age 20 to 60 years. Older individuals showed reduced energy expenditure. Tissue metabolism thus appears not to be constant but rather to undergo transitions at critical junctures."

To translate this and other parts of the study into something more comprehensible for an everyday Joe, the study suggests that there are four stages of metabolism: 

  • From one week old up until age one, your metabolism is at its highest level, "accelerating until it is 50% above the adult rate"
  • Surprisingly, from age 1 to 20, metabolism slows down gradually at about a rate of 3% per year
  • Even more surprisingly, between ages 20-60, your metabolism doesn't change at all, from a physiological point of view anyway
  • From 60 onwards, it slows down by about 0.7% a year

Based on this data, the sad truth is that your weight gain is probably the result of the over-consumption of energy over a long period of time, however uncomfortable this might sound.

Similarly, metabolism seems to not decline at the onset of menopause as previously thought. "This is a positive finding as I believe that if a person/woman keeps “healthy” and fit, there should be no reason why he/she should put on weight at least until they are 60 years old", adds Olga.

Understanding fat and its effects on the body is a whole different story we won't discuss here. In summary, people who accumulated a large amount of fat over decades might find it almost impossible to lose weight in a meaningful and sustainable way.

That's because the body will always fight back against efforts to depart its fat which acts as an energy reserve and is essential for daily energy management, regardless of how large it is. Not an impossible task but not a walk in the park either.

And it's just age-related metabolism facts that got abolished. As the aforementioned New York Times article also says that "Once the researchers controlled for body size and the amount of muscle [mass] people have, they also found no differences between men and women." Everyone needs to work equally as hard to lose weight it seems.

new metabolism study: person running across a bridge

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Is there a point in trying to accelerate metabolism?

Some might get disheartened looking at these results. It's similar to when Nietzsche declared that "God is dead": from now on, you won't be able to blame gradual weight gain on your ageing – it's really just you overeating over a long period of time and living a sedentary life.

The paper also throws a spanner in the works, at least seemingly, in terms of the effectiveness of exercising. Don't get fooled, though, as working out is still the best way to keep the body in check in the long run. After all, the researchers "controlled for... the amount of muscle [mass] people have", meaning if you have more muscle, you'll burn calories.

"Muscle mass has always been considered much more metabolically active tissue (compared to bone mass and fat mass) hence the more muscles a person has, the more calories he/she burns", Olga explains.

"It's a 'use it or lose it' kind of situation with muscle mass as we age", says Matt Gardner, Nutritional Therapist specialising in sports nutrition, "If you're not looking after that metabolically active tissue, it's quite easy to get into a calorie surplus."

This doesn't mean you have to start pumping iron in the nearest gym you can find ASAP, nor that you need professional bodybuilding-level muscle mass for it to elevate your basal metabolic rate efficiently. Many different forms of resistance training can help you build muscle mass, including kettlebell training, resistance band workouts, suspension trainer sessions (using your body weight as resistance), and more.

new metabolism study: person performing the dumbbell bench press exercise

Pumping iron is strictly optional

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Of course, resistance training is only one part of a successful, long-term weight loss program. You'll also need to adjust your diet – that's what got you in the pickle in the first place – plus burn off the calories by doing some form of cardio training. Running or cycling might come to mind first as viable options, but even activities such as brisk walking can help shift some of the stubborn fat.

"Not surprisingly, the research also found that although the metabolic rate patterns held for the population, individuals did differ quite significantly, by as much as 25% slower or faster", says Olga, "This again shows how different we all are and points to several various factors that could potentially determine or influence our metabolism."

Remember, weight gain took years to happen; it won't disappear overnight, no matter what Instagram or TikTok influencers might try to make you believe. As long as you persevere, you will see sustainable weight loss results eventually.

Matt Kollat
Matt Kollat

Matt is a fitness fanatic (a.k.a. fitness and nutrition writer) who's been rambling on about all things health and fitness for over two years now here at T3. His achievements include a short-lived fitness podcast called Fit Mentality Podcast and being a judge on the Fit&Well Awards 2021. In his free time, he works out at home, runs, cycles and loves a good ol' walk around the city. He writes about general fitness stuff, fitness tech, workouts, workout gear/equipment, nutrition and much, much more.