Why Does Metabolism Slow Down As You Grow Old?

What slows our metabolism as we age?

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What slows our metabolism as we age?
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Cryogenic pods and Dorian Gray’s surreptitious deals over his soul, to name a few, might promise eternal youth and immortality, but unfortunately, until they become a reality for you and I, lesser mortals like us have to face the consequences of ageing. The inexorable passage of time leaves behind several travails in its wake which include - wrinkling, joint pain, fatigue and behold, the worst of them all - weight gain. In a nut-shell, one of the biggest factors of weight gain that comes with age is slow metabolism.

Metabolism is defined by Dr Anjana Bhan, Senior Consultant, Endocrinology, Max Mutli-Speaciality Centre, Panchsheel Park, New Delhi, as the sum of all chemical reactions that keep the body alive and organs functioning properly.

In simple terms, metabolism is the process in which your body turns food into energy. Dr (Brig) Pankaj Puri, Director Gastroenterology, Hepatology, Fortis Escorts Hospital, New Delhi, puts it in the following manner:

Metabolism is a complex process during which energy from the calories in the food we consume are used by the body for its normal functioning. Processes like breathing, blood circulation and cellular repair require energy even when the body is at rest. The rate at which calories are burnt for these functions is a body’s basal metabolic rate.
Dr (Brig) Pankaj Puri, Director Gastroenterology, Hepatology, Fortis Escorts Hospital

Understanding Basal Metabolic Rate

There are several factors that determine an individual's BMR, according to Mayo Clinic. They range from the body size (a bigger or more muscular person will burn more calories at rest than an otherwise smaller person), gender (since an average man is more muscular than an average woman, he would burn more calories) and age.

With age comes a fall in muscle mass and increase in the proportion of fat in the body. Consequently, the latter accounts for more of the body weight, thereby slowing down caloric burning.

In addition to this, there are three things that determine the speed of metabolism, that is the rate at which your body is burning its calories, according to Dr Bhan:

  • Resting Metabolic Rate: RMR or calories burned while resting or sleeping. It is the least amount of calories needed to keep a person alive. This is driven by sodium/potassium pumps that generate nerve impulses, and mitochondria, the main power centre of the cell. Mitochondria becomes less efficient and decreases in number with age, becoming a link between ageing and slow metabolism.
  • Thermic Effect of Food: TEF is the calories burnt through digestion and absorption of food. Generally it is about 10 percent of the calories used in a day.
  • Exercise: While calories can be burnt through exercise, which can also increase the rate of metabolism, there is also non-exercise activity thermogenesis or NEAT. This includes standing, fidgeting, cleaning, cooking, playing a musical instrument and so on. Both of these together can constitute from 10 to 30 percent of caloric usage every day.

But What is Slowing This Rate of Metabolism?

'While you may be a fit person and eating a clean diet, you may still notice that after a certain age, it takes an extra effort to achieve similar results as before.'
'While you may be a fit person and eating a clean diet, you may still notice that after a certain age, it takes an extra effort to achieve similar results as before.'
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While you may be a fit person and eating a clean diet, you may still notice that after a certain age, it takes an extra effort to achieve similar results as before. Why does it become harder to shed the same kilos which you could earlier drop in a wink, but now need to up your exercise and diet game regularly to get rid of them? Dr Bhan offers an answer.

Metabolism slows after 30 years of age. Muscle mass also decreases by 3-8 percent each decade after 30. Research has shown that being less active and losing muscle mass has the greatest negative effect on metabolism.
Dr Anjana Bhan

The BMR drops with age in a linear fashion, according to this report. It further points out that there is a fall in skeletal muscle of the body which further directly affects the rate of metabolism.

To list it down, this is all that is happening in your body with age that leads to weight gain and slow metabolism:

● Fall in BMR

● Fall in skeletal muscle therefore fall in the number of calories burnt during exercise as well as when at rest. From this follows the next point.

● Fall in the number of calories burnt during the same exercise and physical movement done before. As a result energy being used by the body decreases.

● Consequently, more muscle is replaced by fat in the body, further making weight loss harder and a more intensive activity.

The key is, to start building muscle as early in your adulthood as possible to fight the fat which starts accumulating with age.

Dr Bhan explains these ways to fight slowing metabolism in more detail.

Countering Metabolism That Slows Down With Age

The fall in the rate of metabolism perhaps begins to show its most significant signs around the mid-thirties for most people. However, it can be countered at any age, by following these solutions offered by Dr Bhan.

  • Resistance and weight training.
  • High intensity interval training (HIIT). In such a routine, calories continue to burn even after the exercise through a process called the afterburn effect.
  • Getting adequate sleep which helps with cell repair.
  • Eating adequate protein. Body burns more calories while digesting proteins than fat or carbohydrates. Protein also helps with muscle building, resulting in a win-win situation.
  • Avoiding a low calorie diet. This can slow down metabolism by pushing the body in what is known as ‘starvation mode’.
  • Consuming coffee and green tea in regulated amounts. Their caffeine content can increase the rate of metabolism.
  • Being alert and aware of medical conditions like hypothyroidism, steroid-use, antidepressant drugs, PCOS, stress and anxiety that can slow metabolism.

Further, ageing is mostly accompanied by a sedentary lifestyle - due to jobs, familial responsibilities and general fatigue that could sometimes also be the result of medical conditions. As a result, age-related weight gain could be triggered by several factors and is often a two-way road. Medical conditions come with age while ageing might get amplified or paced up due to medical conditions. The best that can be done to combat this is to stay fit and eat a clean diet. This in turn would ensure a high metabolic rate, plus an overall protection from medical ailments, thereby aiding you stay in your best shape.

(Rosheena Zehra is a published author and media professional. You can find out more about her work here.)

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