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New Study Challenges What We Think We Know About Metabolism

In a new study published in August 2021 in Science, we learn some shocking new findings that change our whole view of how metabolism works. In this study, one of the largest ever done on metabolism, researchers reveal that we can’t blame weight gain on a slowing metabolic rate

Turns out that it’s not until you reach your 60s that your metabolism, or the rate at which you burn calories, actually slows down. And after adjusting for size and percent body fat, there’s not much difference between the metabolic rates of men and women

So what exactly did researchers find and most importantly, what does this mean for your weight loss goals? We dug into the details of this brand-new study to find out. Read on to learn more… 

What Are the Results of the Research?

Using data from nearly 6,500 people, ranging from ages 8 days to 95 years, researchers discovered that there are four stages to metabolism:

  1. Infancy: Up until age 1 your calorie burning is at its highest, accelerating up to more than 50% of the adult metabolic rate. 
  2. Ages 1 to 20: Your metabolism gradually slows down by about 3% every single year.
  3. Ages 20 to 60: Your metabolism levels off and holds steady.
  4. After age 60: Your metabolic rate begins to slow down about 0.7% every year. 

The larger or more muscle mass you have, the more calories you burn throughout the day. But after adjusting for these body size and muscle mass factors, researchers found that there is no difference between the metabolism of men and women

What Do These Results Mean?

Before this study, the common belief around metabolism was that your built-in calorie-burning system starts slowing down as you enter your 20s. And it continues to decline as much as 2-4% every single year. For women, this metabolic rate is even slower, especially during menopause. 

Turns out, all this is incorrect. 

This study contradicts everything we thought we knew about metabolism. Here’s what we learned:

  • Your metabolism is stable from your 20s through your 50s, with life events like menopause and pregnancy having little impact on that metabolic rate.
  • It’s actually during your infancy, not your teenage years, when your metabolism is at its highest. 
  • A man and a woman of the same age, height, and body fat have the same metabolic rate

What’s So Different About This Study?

So why have we never discovered this before? Turns out that most research on metabolism has been pretty limited in size and scope. Metabolic research is expensive, so for the first time in this study, multiple labs decided to pool their resources and share their data to get a larger sample size.  

This international team of over 80 researchers collected data across 40 years using the popular “doubly labeled water” method, considered the gold standard for measuring energy expenditure. 

In the doubly labeled water method, participants drink water where the hydrogen and oxygen molecules have been replaced with isotopes of these elements. Using urine samples, scientists can then calculate how much carbon dioxide, a natural byproduct of burning calories, your body is producing throughout the day.

Over 6,500 people across 29 different countries performed this test. Only when researchers pooled that data together and measured it separately from height and weight did they notice a trend contrary to what we’ve long understood about metabolism.  

Like most research, this leaves us with more questions than answers. But one thing is clear from these results: your metabolism changes over your lifetime, but it’s not what we originally thought. 

What Does This Mean for Weight Loss?

This means we can’t use metabolism as an excuse for weight gain. And that might feel frustrating or discouraging. 

But this better understanding of metabolism is a good thing for your weight loss goals. Because now instead of focusing on something you can’t control (metabolism), you can shift the focus to something you can control (your diet and lifestyle). 

If it’s not a slowing metabolism putting on the pounds before the age of 60, that means there are other factors at play. This could be: 

  • Baby weight from pregnancy
  • Changes in your activity levels as you age (busier schedules, greater family obligations, less exercise, and so on)
  • Shifts or changes to your diet
  • Medical conditions impacting your health
  • Higher levels of stress
  • Change of location or lack of healthy food access 
  • Less sleep, etc. 

So although it’s common to gain weight as you get older, it’s not a slowing metabolism but rather a complex combination of life factors that might be the cause. 

If those life changes are leading to unhealthy weight gain it’s only by understanding its cause that you can find a solution. This is what moves the dial on your weight loss goals and why everyone’s journey to healthy weight loss looks so different. Because we all have different factors contributing to our overall health.

Focus on Diet Instead of Metabolism

Although the reason for weight gain from our 20s through our 50s is different for everyone, there is one common thread amongst them all: diet

Certain life events as we age impact our diet…

  • A divorce or breakup throws you into an unhealthy spiral
  • A medical condition impacts your eating patterns
  • A promotion keeps you at work for longer hours substituting frozen meals in replacement of healthy whole foods
  • Or a new addition to the family makes eating healthier even harder

Life looks different as you age! And sometimes that weight gain is perfectly normal. But for many Americans, this results in a higher intake of calories than the body can burn off, leading to unhealthy weight gain and rising levels of obesity. 

 And it's not just the amount of calories we’re consuming that’s the problem, but the quality of those calories. With increasing levels of sodium, unhealthy fats, added sugars, and processed foods in the average American diet, we’re feeding our bodies empty calories instead of the nutrition it needs.

So, what’s the solution? Clean and healthy eating and a diet that works for your individual needs and schedule. That’s why at 310 our focus is not just on cutting back unwanted calories through our 310 Shakes, but also on shifting your eating and lifestyle habits. 

It’s not about counting calories but about making those calories count.  

We do this by focusing on whole foods, healthy fats, fiber, protein, and complex carbohydrates. By eating foods that fill you up instead of leaving you feeling empty. And as you reach the age of 60, learning to adapt your diet to meet your changing metabolism and reduced hunger levels. 

The Big Takeaway

Your metabolism does decline as you get older, but not until you reach your 60s. That means the key to weight gain in your 20s through your 50s isn’t your shrinking metabolism, but other factors that might be at play

Keep a food diary, track your eating patterns, observe any lifestyle changes you might be experiencing or talk to your doctor. These will be the key to understanding your unwanted weight gain and finding your path forward towards healthy weight loss. 

And remember that 310 Nutrition is here to help! 

Check out our resources below for more information on healthy weight loss and finding a solution that works for you:

  • 310 Community: supportive guidance, recipes, and more! 
  • 310 Blog: access to unlimited resources and healthy weight loss information 
  • 310 Recipes: delicious shake recipes to help support your weight loss goals


Written by:

Megan Elizabeth Clark

310 Nutrition Content Writer 

Megan Elizabeth Clark is a freelance copywriter and content marketing specialist in the health, wellness, and fitness industry. As a NASM certified personal trainer and RYT-200 certified yoga instructor Megan is passionate about using her fitness background and writing skills to provide authentic, actionable, and accurate information to the world [...]

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