Why Does BMR Decline with Age?

As people grow older, they often feel the many changes that come with age. This includes a decline in muscle mass, having less energy for strenuous activities, and in some cases, aches and pains that pop up out of nowhere. For those who are conscious about their health and fitness, one of the most telling signs of age is a slower metabolism.

A slower metabolism usually manifests itself in different ways. However, the most telling is weight gain. This is because the body’s metabolism (or Basal Metabolic Rate), decreases as one grows older. Your BMR is the number of calories you burn to maintain your normal bodily functions even while at rest. All these calories are used to maintain your blood pressure, brain function, breathing, body temperature, and more.

You can use a BMR calculator to help you determine if your BMR is within the normal range. For men, the average BMR is at around 1600 calories a day. The number is slightly lower for women at 1400 calories a day. If you take a look at the calculator, you’ll need to input your weight and height, along with your age—a huge factor for determining BMR.

Try increasing the age you put into the BMR calculatorand you’ll see that the BMR decreases as the age goes up. So why does BMR decline with age? Here are some of the reasons:

You’re less active.

As people age, they tend to have less energy than they used to. When you’re in your teens and 20s, you had so much energy that you could do so much in one day. You could go to school, go to work, hang out with friends, and exercise all in the same day.

However, when you reach your 30s, 40s, and 50s, it takes a lot less for you to feel tired. This is especially true for people who lead more sedentary lifestyles (e.g. sitting at an office all day, etc.).

Combine the lack of energy with more responsibilities. Perhaps you have more work to do or have more children to take care of. This gives you less time to exercise, which in turn can weaken your lean muscles.

Your body composition has a huge effect on your BMR. Your body requires more calories to maintain lean muscles. But if you have less lean muscles due to lack of exercise, your BMR drops. That’s because your body has less lean muscles to maintain when at rest.

You have less muscle mass.

Muscle mass steadily decreases as you age. This is a natural occurrence called sarcopenia, wherein you can lose up to 5% of muscle mass every decade after you turn 30.

It may have been easy to build up muscle when you were younger, but the older you get, the harder it becomes. Sometimes, it’s due to poorer endurance. A combination of less energy and less muscle tonality come into play as well. This is why even if you maintain the same workout routine from your younger years, you either can’t build up the same amount of muscle mass or you end up feeling more tired.

As mentioned above, when you have less muscle mass, your BMR also decreases.

Your metabolic process slows down.

It may seem redundant to say that your metabolism slows down with a lower BMR. However, your BMR isn’t the only factor involved in your metabolic processes. You burn calories at a rate that’s determined by the chemical reactions in your body. These reactions are driven by two cellular components: mitochondria and sodium-potassium pumps.

The mitochondria use oxygen to create energy for your cells. The sodium-potassium pumps, on the other hand, generate signals that keep your nerves, muscles, and organs working.

As you age, both the mitochondria and sodium-potassium pumps become less efficient at their jobs. Since these two components are so important for bodily functions, their slowness affects your BMR immensely. This is why you feel a little more sluggish as you grow older as well.

You maintain the same diet.

Back when you were younger, you could eat as much as you wanted without gaining a lot of weight. However, as you age, your metabolism gradually slows down. If you maintain the same diet you had when you were younger, all the food you eat gets stored instead of burned into energy. Combine that with a less active lifestyle, and your food gets stored as body fat. If you store more body fat, your BMR declines.