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Metabolic Health

What Is Metabolic Age and Why It Should Matter to You

By Brady Holmer
Metabolic age, unlike chronological age, is a measure of aging and integrity within your cells and tissues. Lifestyle factors like diet, exercise, and environmental and emotional stress can accelerate or delay metabolic or biological aging.

Everyone ages — it’s one of the indisputable facts of life. From the moment we are born, each one of us starts a linear process of growth and maturation, aging a bit more each day, experiencing, as Alex Comfort of Joy of Sex fame wrote in 1972, a “decrease in viability and an increase in vulnerability.”1 As of yet, we don’t have the technology to turn back time, which means our traditional concepts of aging will stay as they are for now.

But viewing aging as a passive process outside our control is becoming an outdated concept, especially in the eyes of scientists working on the biology of aging. While we can’t slow down time itself, we can do things to alter the trajectory of aging and perhaps slow down the rate at which we physically and mentally age. New science is showing that how old we are in years might not reflect how old we are on the inside, which is good news for those who want to take control of their own aging journey.

For those who claim that they “feel better now than I did when I was 20,” there may be some truth to your statement.

WHAT IS AGING?

When someone asks, “How old are you?”, the typical answer is a specific number of years. This is your chronological age — how many years you’ve been alive on earth, or your actual age.

When we speak of aging in the traditional sense, we are talking about chronological aging.

Typical views of aging involve an “increasing probability of death with increasing chronological age.” While perhaps a bit unpleasant, these are the facts of life. Chronological aging is also associated with a greater likelihood of several major diseases including cardiovascular disease (CVD), cancer, chronic lower respiratory disease, diabetes, and Alzheimer’s disease, and dementia.1

Why we age is complex and involves many cellular and molecular processes but, in general, increasing age brings an increase in cellular damage and a “loss of molecular fidelity.” A cornerstone of modern biology and aging theory is that aging is driven by a “purposeful genetic program” — implying that we may have very little control over the process.2

This “traditional” theory of chronological aging, however, is slowly being replaced by more modern views on the biology of aging — views that are more accepting of the malleability of the aging process.

WHAT IS METABOLIC AGE?

In contrast to chronological aging, metabolic aging, also known as biological aging, actually reflects the aging process that goes on inside our cells and tissues.

With each passing day and year, our bodies are subjected to the effects of chronic inflammation, cell breakdown, mitochondrial DNA damage, stem cell depletion and cellular senescence.1 These “theories of aging” attempt to explain the cellular processes behind why aging is associated with reduced functionality and a greater likelihood of disease.

Metabolic or biological aging is the result not of a single genetic program, but rather the random accumulation of many “stochastic” events outlined above. Aging, according to pioneering aging scientist Leonard Hayflick, is “an increase in molecular disorder.” This disorder occurs because our body becomes less efficient at repairing, turning over, and replacing worn-out or senescent cells. DNA, proteins, mitochondria, and other cellular structures become damaged, and when molecular disorder within cells exceeds our capacity to repair this damage, cells undergo changes that we refer to as aging.2

Metabolic age is the relative age of your cells and tissues and the damage they’ve accumulated. Metabolic age does not reflect a single genetic program, but rather many converging programs and can be affected by external factors.

HOW IS METABOLIC AGE DIFFERENT FROM CHRONOLOGICAL AGE?

We all age the same chronologically. Two people with the exact same birth date, down to the month and day, have the same chronological age.

Not so with metabolic age. The “molecular disorder” underlying the biological aging process varies from cell to cell and from tissue to tissue. Cells undergo changes at a different rate in your heart, brain, and lungs. Leonard Hayflick analogized this to a “clock shop” — there is very little chance that all of our molecular “clocks” are recording the passing of time identically.2

Cells within an individual “age” at a different rate, and so do people. This means that unlike chronological age, metabolic age can vary widely among individuals. Just because two people have the exact same chronological age does not mean they have the same metabolic age.

Think of two individuals, both 70 years of age. One is pretty inactive, not as mentally aware, and perhaps has lost some of their joie de vivre. The other, also in their eighth decade of life, has retained their youthfulness, vigor, and mental clarity. Disease, frailty, and cognitive decline are experienced by these two individuals at different rates. This illustrates the concept of metabolic age.

You may be asking why metabolic age is important? Metabolic age is a different and perhaps superior measure of your true age than chronological age because it takes into account factors including lifestyle, diet, genetic history, and disease conditions, and how these factors affect your aging process and overall vitality.

Metabolic age is the relative age of your cells and tissues and the damage they’ve accumulated. Metabolic age does not reflect a single genetic program, but rather many converging programs and can be affected by external factors.”

HOW IS METABOLIC AGE MEASURED?

The single numerical label giving your chronological or “actual” age is likely not an ideal way to quantify your quality of aging. Luckily, developments in modern aging science have brought us new ways to measure molecular and cellular processes that may provide insight into our “true” metabolic or biological age.

One of the traditional theories of aging puts forth how quickly we age may be the result of our basal metabolic rate, also known as BMR. This is known as the “rate of living” theory of aging.1 BMR is the amount of calories, or energy, that you utilize to maintain bodily functions. Metabolism produces energy, but also molecules called free radicals, which have been shown to contribute to the aging process by causing cell and DNA damage. Measuring BMR to indicate your “rate of living” and therefore rate of aging is proposed as one way to measure “metabolic age,” but some studies have found that a higher BMR may not actually lead to more oxidative stress, and may not be the best indicator of your true metabolic or biological age.3

For this reason, scientists are looking for biomarkers that might better predict your true metabolic age. A “biomarker” of age is a quantitative variable that can be measured (typically in a blood or tissue sample) to indicate your biological age.

Several laboratory biomarkers have been developed and tested as biomarkers of aging. For instance, simple clinical biomarkers including inflammation, glucose metabolism biomarkers, and thyroid hormone levels have all been shown to predict disease outcomes and mortality and could be one way to get a snapshot of one’s biological age.1

However, more advanced genetic methods of measuring biological age have taken the spotlight and grabbed the interest of aging biologists — telomere length and the “epigenetic clock.”

Telomeres are caps on the ends of our chromosomes that protect them from DNA damage. Think of them as the plastic aglets on the end of shoelaces. Every time a cell divides, telomeres shorten (the shoelace frays). The shortening of telomeres causes cells to grow nearer to their replicative capacity — also known as the “Hayflick Limit.” An enzyme called telomerase can help to replenish lost telomere DNA and “regrow” telomeres, but diminishes with age.1 For this reason, telomere length and the amount of the telomerase enzyme have both been proposed as biomarkers of aging. And while many have proposed that telomeres may play a critical role in the aging process, there is currently not enough evidence that telomere shortening is a valid measure of biological aging, and telomere length may not accurately predict one’s true biological age.4,5 More accurate and standardized tests of telomere activity could someday allow them to be a valid way to measure biological age.

Another promising biomarker for metabolic age is known as “Horvath’s clock.” This “clock” was developed by Steven Horvath and team in 2013 at UCLA. Also known as the “epigenetic clock,” Horvath’s clock measures epigenetic markers on DNA — known as methylation — to estimate one’s rate of aging. DNA methylation is the process of substitution of a hydrogen molecule in organic compounds with a methyl group. This change in methylation is directly proportional to age, so the greater your “methylation,” the higher your metabolic or biological age. “Horvath’s clock” is an accurate indicator of biological aging, with a +/- 2.7 years margin of error for indicating the rate of aging.1 Measuring DNA methylation using epigenetic clocks may be one of the most robust age biomarkers available to date, and this area is sure to explode in the coming years as better, more accurate techniques are developed.5

Measuring metabolic or biological age will provide the ability to find a discrepancy between one’s chronological and biological age, finding those who are “epigenetically older” or “epigenetically younger” than their true chronological age.

What is so intriguing about the epigenetic clock is that it allows the measurement of metabolic or biological age in many different tissues, providing a more accurate and complex view of the aging process and an insight into how various lifestyle factors and interventions may influence aging within individuals.

WHAT RISK FACTORS INCREASE METABOLIC AGE?

A long life expectancy might run in families due to “good genes.” However, when it comes to biological age, lifestyle factors may be the single most important determinant of how quickly your biological clock ticks.

Traditional risk factors like high blood pressure, cholesterol, and blood glucose are great for assessing cardiovascular and metabolic disease risk and are likely related to metabolic and biological aging. But when considering factors that increase metabolic or biological age, it may be more important to discuss lifestyle factors that have been shown to play a major role in the aging process.

Smoking and high alcohol consumption are linked to epigenetic changes that could increase biological age. This is because both cigarette (and perhaps e-cigarette) smoke and alcohol contain toxic, pro-inflammatory, and some pro-carcinogenic (cancer-causing) compounds that likely accelerate processes linked to biological aging. Furthermore, high alcohol consumption and smoking can cause epigenetic changes associated with a faster rate of aging.6

Environmental pollutants (air pollution) and high emotional, physical, and psychological stress may also contribute to speeding up the genetic clock, and limiting one’s exposure to these “stressors” is one way to reduce the rate of metabolic aging.6

Diet, physical fitness, and body composition are important factors for determining biological age. Diets high in sugar may be one of the most detrimental things to health and aging, as demonstrated by the association of sugar consumption with diabetes, dementia, and cardiovascular disease — all “diseases of aging”. Being overweight or obese is a significant risk factor for disease and a likely contributor to increasing one’s biological age.1 This may be largely due to the negative effects of having a large amount of visceral fat (fat stored around the abdomen). Visceral fat has been shown to be pro-inflammatory and may interfere with the effects of insulin, promoting metabolic dysfunction.7

By limiting exposure to negative lifestyle factors that increase the rate of aging, you can perhaps ensure that your biological age progresses slower than your chronological age.

HOW TO IMPROVE YOUR METABOLIC AGE

Preventing unwanted or “accelerated” aging can be done by avoiding negative lifestyle factors. But what can we do to actually improve or reduce biological age, if anything?

For one, maintain a healthy body weight and keep blood pressure, cholesterol, and insulin and glucose levels within normal ranges. These risk factors are involved in metabolic and cardiovascular regulation, and studies have shown that they are related to a slower rate of epigenetic aging.8

A diet high in polyphenols may contribute to reducing biological age. Polyphenols are natural compounds that have been shown to modify epigenetic markers including DNA methyltransferases, histone acetylases, and histone deacetylases — which are intricately involved in biological aging.6 A recent study found that a diet high in fruits and vegetables (which contain high amounts of polyphenols) was associated with anti-aging effects on the “epigenetic clock.”8 Other dietary factors associated with a lower epigenetic age include consumption of fish and poultry. This suggests that eating a diet high in lean meats, fruits, and vegetables may be one way to lower your biological age, likely due to the effects that the nutrients found in these foods have on your DNA.

Physical activity can also “turn back” the biological clock. Higher physical activity levels are associated with slower epigenetic aging, and exercise training has been shown to reduce biological age, likely due to the effects of exercise on DNA methylation and other epigenetic processes.8,9 Regularly breaking a sweat improves the function of your metabolism, builds muscle mass to protect against frailty and sarcopenia, and increases aerobic and cardiorespiratory fitness — exercise is anti-aging in the most complete sense and is one of the best ways to keep a youthful metabolic age.1

For those who want a less “vigorous” way to slow down metabolic aging, there is some evidence that meditation can actually reduce biological age.10 This is likely due to the stress-reducing effects of a meditative practice or maybe the fact that long-term meditators may be less “stressed out” than non-meditators. Either way, finding ways to reduce stress levels is another way to positively alter the trajectory of biological aging, since it is well known that higher stress can cause and accelerate biological aging.6

AGE IS JUST A NUMBER

The number of candles on your birthday cake might not say as much about your actual age as we once thought. As the science of aging uncovers more about how and why we age, it is becoming clear that age is truly “just a number.” How old we really are, that is, our biological age, can be influenced by what we eat, how we move, and our everyday exposures. The good news is, it appears that it’s possible to slow down the rate at which we age, and perhaps even reverse our biological age.

The saying “60 is the new 40” might be true after all, so long as you take the right steps to become more actively involved in your own aging process. The good news is that aging is not a predestined outcome.

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