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The Metabolic Mystery: Why Do We Gain Weight As We Age?

Have you ever heard someone say (or maybe even said yourself),

“Ever since I turned “X” age, I just can’t seem to lose weight.”


“It used to be so much easier. When I was 20, I could eat whatever I wanted, and the weight would just fall off.”

Our metabolism often gets the bulk of the blame when looking for the culprit of unwanted weight fluctuations as we age.

We're often told our metabolism speeds up at puberty and slows down in middle age, particularly with menopause, and that men have faster metabolisms than women.

But is this true?

Well, let’s find out.

A groundbreaking study, led by Herman Pontzer and colleagues assembled an extensive, diverse database that encompassed more than 6,421 individuals, male and female, aged between 8 days and 95 years to shed light on the intricate dance between aging and metabolism.

This blog aims to explore common myths, clarify misconceptions, and reveal the real reasons behind age-related weight gain, providing a clearer understanding of our metabolic journey through life.

The Metabolism Myth

One of the most pervasive myths is that a dramatic slowdown in metabolism directly correlates with aging, leading to inevitable weight gain.

The assumption goes that as we get older, our body’s ability to burn calories diminishes, making it harder to maintain or lose weight.

However, the collaborative metabolic study led by Pontzer, challenges this notion, revealing a more nuanced picture of how our metabolism actually changes over the lifespan.

The Four Phases of Metabolic Rate

The research identifies four distinct phases of metabolic changes from infancy to old age, debunking the one-size-fits-all decline theory.

From birth to age one, infants experience a rapid metabolism, burning calories much faster than adults (about 50% more than you’d expect based on their size).

Metabolism stays elevated through childhood, slowly decelerating through adolescence to land at adult levels around age 20.

Perhaps the biggest surprise was the stability of our metabolism through middle age.

Daily energy expenditures hold remarkably steady from age 20 to 60. No middle age slowdown, no change with menopause.

Same goes for the metabolic differences between men and women. Women have lower daily energy expenditures on average, but that is only because women tend to be smaller and carry more of their weight as body fat vs. lean tissue.

If you compare men and women with the same body weight and body fat percentage, the metabolic difference disappears.

So, based on this, the weight gain so many of us experience in adulthood cannot be solely blamed on a declining metabolism.

Now with that said, metabolism does decline as we age.

However, it doesn't kick in until we hit 60. After 60, metabolism slows by around 7 percent per decade.

By the time men and women are in their 90s, their daily expenditures are 20 to 25 percent lower, on average, than those of adults in their 50s (accounting for body size and composition).

So, if it isn’t our declining metabolism, what’s really to blame for stubborn weight gain as we age?


The Real Culprits of Age-Related Weight Gain

If our metabolism remains relatively stable through most of adulthood, what causes the common weight gain associated with aging?

The study points to changes in lifestyle and body composition rather than a slowing metabolism.

As we age, muscle mass tends to decrease, and fat deposits increase. Since muscle is more metabolically active than fat, this shift can lower the number of calories our bodies burn at rest.

Additionally, physical activity often decreases with age, further reducing calorie expenditure.

This insidious cycle of less activity, lean muscle loss and body fat increase, creates a metabolic disaster that can make you feel like you’re fighting a losing battle.

Lifestyle Over Genetics

Another myth is that our genetic makeup is the primary determinant of our metabolic rate and, by extension, our weight.

While genetics do play a role, lifestyle choices have a far more significant impact.

Regular physical activity, including resistance training to build muscle, can counteract the effects of aging on metabolism.

Pro Tip: Resistance Training a minimum of 3 days per week and getting in 8,000+ daily steps will drastically reduce the effect of sarcopenia (naturally occurring lean tissue loss as we age) and maximize your metabolism, so you feel young and vibrant deep into your later years.

A balanced diet, rich in nutrients, also supports a healthy metabolic rate by providing the energy and materials our bodies need to function efficiently.

Pro Tip: Aim for at least 1 gram of protein per pound of body weight (or goal weight) per day. This will help to build/keep your hard-earned muscle for a strong capable body and robust metabolism regardless of age.

Zoom Out

Focusing solely on metabolism as the key to weight management overlooks the broader picture of health.

It’s like treating a symptom rather than the root cause.

The study underscores the importance of considering overall energy expenditure, including physical activity and dietary intake, rather than blaming metabolism alone for weight gain.

Maintaining a healthy weight as we age involves a multi-pronged approach to our overall lifestyle, encompassing diet, exercise, and other factors like stress management and sleep quality.

Once those key pillars are in place, you and your metabolism can get back to being a forged alliance, instead of friends lost due to a misunderstood conversation.

The Best Part

The study by Herman Pontzer and colleagues provides a fresh perspective on the relationship between aging and metabolism, challenging long-held beliefs and offering evidence-based insights.

It highlights that the stability of our metabolic rate through much of adulthood offers a window of opportunity for maintaining health through lifestyle choices.

Age-related weight gain is less about an inevitable metabolic slowdown and more about the complex interplay of physical activity, diet, and body composition.

Understanding these dynamics empowers us to make informed decisions about our health, debunking myths, and freeing us from becoming victims of circumstance.

It’s our diligence, and commitment to lifelong health that will determine how we age.

Ultimately, blaming metabolism for weight gain is like blaming the rain for getting wet when you chose not to open the umbrella you're holding.

The power has always been, and always will be, in our hands.

Committed to your Success,

Coach Michael

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