Why your metabolic age matters

Metabolic age is a word that is bandied about a lot by fitness gurus. But what is metabolic age and what does it signify? If it is too high, how can you improve it? And is it relevant when you are trying to beat your diabetes?

Metabolic age is just a simple number. However it considered a useful indicator of the overall level of your health and fitness.

The number is obtained by comparing your Basal Metabolic Rate (BMR) with the average BMR of other persons who are the same age in years as you.

If your metabolic age is lower than your actual age, you are fitter and healthier than the average for your age group. But if your metabolic age is higher than your chronological age, it indicates that you need to improve your level of fitness.

This explanation begs the question … what is your basal metabolic rate?

Firstly, to answer this question, we need to discuss metabolism.

What is metabolism

The term metabolism refers to all the chemical transformations that take place in your body …. changes that are vital for sustaining your life.

These transformations are many and varied, and include:

  • your digestive processes … the complex biochemical processes by which what you eat and drink is combined with oxygen to release the energy your body needs to function
  • the transportation of substances into and between cells
  • the conversion of glucose inside your cells into the energy that the cells need to function
  • the conversion of food into the building blocks for proteins, lipids, nucleic acids etc
  • the elimination of nitrogenous wastes

These changes allow your cells to grow and reproduce, maintain their structures and respond to their environment.

Without them your body simple would not work.

Basal metabolic rate (BMR)

Every day your body must breathe, circulate blood, control its temperature, grow and repair cells, adjust your hormone levels, support the activities of your brain and nerves, and so on … even if you do nothing and just lie in bed all day.

Your basal metabolic rate (BMR) is the number of calories your body burns every day to carry out the basic functions needed to support the normal functioning of your vital organs … heart, lungs, nervous system, kidneys, liver, intestines, sex organs, muscles and skin … while you are at rest.

In other words BMR is the amount of energy expressed in calories that you would need to maintain your body function while resting for 24 hours … as if you were lying in bed all day and night.

Surprisingly, your BMR accounts for 60 to 75% of the total energy you burn each day, ie up to three quarters of the calories you consume is spent on just keeping you alive.

The rest of the energy you burn every day is used up in two ways:

Food processing … just digesting, absorbing, transporting and storing the food you consume uses up plenty of calories. For example, about 10% of the calories you get from the carbs and proteins you eat are expended during their digestion and absorption.

Physical activity … accounts for the rest of the calories your body burns during the day, 15 to 30% of the total energy you use up. It consists of normal every day activities (such as getting up and moving around) plus deliberate exercise (eg, playing tennis, swimming, taking the dog for a walk and so on).

The energy needs for your body’s basic functions, as well as food processing, stay fairly consistent and do not change easily.

However the calories you burn while undertaking physical activities can vary greatly from day to day. Indeed physical activity is the most variable of the factors that determine how many calories you burn in a day.

What influences basic metabolic rate (BMR)

Your BMR is influenced by several factors … muscle:fat ratio, gender, size, and age:

Muscle:fat ratio … or composition of your body, ie whether you have more muscle than fat or vice versa. Just maintaining muscle at rest requires more calories than maintaining fat. So the more muscular you are the higher your BMR will be.

Gender … men usually have more muscle and less body fat than women of the same age and weight, which means that men burn more calories at rest. Research indicates that the BMR of women is 5 to 10% lower than men.

Size … taller and heavier persons have a higher BMR because the more mass you have, the more fuel you need to sustain larger organs. When you lose weight your BMR goes down and you need fewer calories per day. And when you gain muscles your BRM will increase.

Age … your BMR decreases as you get older because you muscle mass declines by 5 to 10% each decade after the age of 40.

Heredity … you can inherit your metabolic rate from your ancestors.

Climate … the BMR of persons living in the tropics is can be between 5 and 20% higher than persons living in temperate zones, because keeping the body cool consumes energy.

How to calculate basic metabolic rate (BMR) and metabolic age

Strictly speaking, your digestive system should be inactive when you are calculating your BMR. But in human beings this takes about 12 hours of fasting. For this reason, the less strict Resting Metabolic Rate (RMR) is calculated in practice instead of BMR.

Calculating your RMR is a cinch. Formulas take into account your age, weight, height, activity level, body fat mass and lean body mass.

Not every formula takes the exact same variables into account. The formulae can vary depending on the preferences of the researcher or gym master who is using them. But for any particular person they all seem to come up with more or less the same answer.

You can find various formulae on the internet. Or you can try this one manually:

RMR = 9.99xw + 6.25xs – 4.92xa + 166xg-161, where:

  • s = height in centimetres; if you know your height in inches, multiply by 2.54 to get your height in centimetres
  • a = age in years
  • g = gender = 1 for males, 0 for females

Once who have worked out your BMR, you can calculate your metabolic age by comparing your BMR (or RMR) with the average for people of your chronological age who are of similar height. If your BMR matches with the average BMR of a lower chronological age then that age is your metabolic age, ie your metabolic age is lower than you calendar age. And vice versa.

To do this, you need a chart of the average BMR for various ages. A long search on Google did not turn up such a chart on the internet but you should be able to get one from your local gym.

How to change your metabolic age

There is not much you can do about your gender, height, age, hereditary traits and the climate you live in.

But you can change the ratio of your muscle to your fat.

Body fat requires much less energy than lean muscle, because lean muscle is much more metabolically active and therefore requires the expenditure of more energy.

If you compare two individuals, both of the same age and weight but with differing ratios of lean muscle mass to fat, the person with more lean muscle mass will have a higher basal metabolic rate, and therefore, a lower metabolic age in comparison to the person with a greater percentage of fat.

There are two basic ways you can improve your metabolic age, increase your muscle mass and reduce your body fat:

  • increase your exercise regime to gain more muscle tissue, and
  • control your intake of calories to ensure that you are getting the right mix of macro-nutrients to support your exercise regime.
Using exercise to improve your BMR

The only sure-fire way of increasing your BMR and reducing your metabolic age is to add strength training to your exercise regime.

Strength training … (such as push-ups, pull-ups and weightlifting) should be undertaken at least twice a week to build muscle and reduce fat. As well as improving your metabolic age, this will counteract the muscle loss associated with aging.

A pound of muscle burns six calories a day while a pound of fat only burns two calories a day, a ratio of 3:1. And every muscle cell you gain burns calories even while you sleep.

The more muscle you build, the higher your BMR will be and the lower your metabolic age, because muscle burns 73 more calories per kilogram a day compared to fat, even while you are resting.

Aerobic exercise … you should get a least 30 minutes of aerobic exercises, such as walking, cycling and swimming, every day. Aerobic exercise burns calories while you are exercising and keeps your metabolism elevated even after you finish.

If you find 30 minutes a day hard to fit into your schedule, try breaking it up into 10 minute sessions or even smaller intervals. Just make sure you do a minimum of 30 minutes a day without fail.

Incidental exercise … there are plenty of ways you can add extra movement to your day and burn additional calories. For example, take the stairs instead of the elevator, wash your car, cycle to work instead of driving, walk to the shops, and so on.

Using diet to improve your BMR

You need to use your diet to support your strength training and exercise routines by eating foods that tend to boost your metabolism.

Small frequent meals … most people eat less overall when they eat small but more frequent meals, say four to six meals a day. This will help you lose weight, ie reduce your fat, thus improving the muscle:fat ratio of your body.

Lean proteins … eat foodstuffs such as turkey, fish, beans and tofu. Eating a diet rich in lean proteins will increase your metabolism because it takes more energy to digest this type of protein.

Spices … such as hot peppers, crushed red pepper flakes or cayenne pepper, as well as hot sauces, added to your recipes can increase metabolism by about 8%. The effects are only temporary but if you add just a little spice each day to your meals your metabolism will continue to be boosted.

Water … studies show that increasing the amount of water you drink can increase you metabolic rate by up to 40%. The reason for this is not clear but it may be due to your body’s attempt to heat the water.

Coffee … has been shown to increase metabolism because of the caffeine it contains. However the metabolic effects are small compared to other measures such as exercise.

Green tea … in combination with diet and exercise can improve your metabolic rate, even if the tea is decaffeinated. Why green tea has this effect is not known. One study showed that combining decaffeinated green tea extract with exercise had a more dramatic effect than exercise alone.

Metabolic age and diabetics

Excess body fat underlies two-thirds of cases of type 2 diabetes in men and more than three-quarters of cases in women.

And, as we have seen, excess body fat is the primary cause of a low BMR and a metabolic age that is higher than your chronological age.

Improving your muscle:fat ratio through strength training, supported by an appropriate diet, will not only improve your metabolism and lower your metabolic age but it will also improve your insulin resistance. And that’s the secret of beating your diabetes.

Author: Paul Kennedy


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