Why Weight Loss Gets Harder as We Age (and How to Boost Metabolism)

Why Weight Loss Often Gets Harder as We Age

As we age, many people notice that the strategies that once helped them maintain or lose weight no longer seem to work as easily as they used to. You might notice that you still eat similarly to how you always did in your 20s or 30s, yet you’re gradually gaining weight. Or perhaps losing weight now feels slower and harder to maintain than it used to.

This experience is incredibly common, and it often gets blamed on a “slower metabolism.” But does metabolism actually slow down with age? The reality is that several subtle changes begin occurring in the body over time, many of which directly affect how many calories you burn each day. Fortunately, many of the factors behind this are not completely outside of your control.

Does Metabolism Actually Slow Down With Age?

For years, it was widely believed that metabolism steadily slowed throughout adulthood, especially after the age of 30. However, newer research has challenged this idea.

In a 2021 study, researchers analyzed energy expenditure across thousands of people from infancy through older adulthood. Researchers found that metabolism actually remains relatively stable throughout most of adult life, particularly between the ages of around 20 to 60. Significant metabolic slowing did not appear to occur until later older age (1).

This finding suggests that age itself may not reduce metabolism dramatically. If that’s the case, though, why does weight gain still become more common with age?

The key reason is that metabolism is heavily influenced by body composition, especially muscle mass, along with movement patterns, hormones and lifestyle changes that often shift gradually over time.

In other words, the issue is often not that the body’s metabolism suddenly slows down when you turn a certain age. Instead, the body may simply be using fewer calories than it once did because of changes occurring within it as we get older.

Why Muscle Mass and Metabolism Change With Age

One of the most significant changes that occurs with age is the gradual loss of muscle mass. Without intervention, research suggests muscle mass begins to gradually decline from mid-adulthood onward (∼1% lost per year), with the rate of loss often accelerating as we age (2).

This matters because muscle is metabolically active tissue, meaning your body requires calories to maintain it, even at rest. Therefore, the more muscle you have, the more calories your body naturally burns throughout the day.

When muscle mass decreases with age, the number of calories you burn at rest also tends to decrease. This means your body may gradually require fewer calories than it once did to maintain the same weight. As a result, eating the same way you always have can gradually lead to weight gain over time.

Here's how it typically unfolds:

• You gradually lose muscle mass
• Your resting calorie needs decrease slightly
• Your eating habits remain the same
• What was once maintenance intake may now become a small calorie surplus (ie, you are eating more calories than your body is burning)
• Even a relatively small daily surplus can slowly lead to weight gain across months and years

This is one of the biggest reasons why people often feel like they are “doing the same things” yet gaining weight more easily as they get older.

What Happens to Metabolism After 40?

Many people begin noticing changes in metabolism after 40. While muscle loss plays a major role in age-related metabolic changes, hormones can also influence how the body stores fat, regulates appetite and maintains muscle mass. As we age, these hormonal shifts can make weight management feel noticeably different than it once did.

For Women: Declining Estrogen

During perimenopause and menopause, estrogen levels decline significantly, and many women begin noticing changes in their bodies that feel frustratingly unfamiliar. Weight may start accumulating more around the abdomen, even though eating habits have not changed dramatically. It’s also common to notice feeling hungrier more often, less satisfied after meals or that the same habits no longer maintain weight as easily as they once did. Hormonal changes during this time can influence appetite, how the body stores fat and how efficiently the body uses energy.

At the same time, muscle mass and daily movement often decline gradually with age, which can reduce the number of calories the body burns each day. Together, these changes can make weight gain feel easier and weight loss feel noticeably harder than it once did.

For tips on how to boost metabolism during menopause or perimenopause, continue reading below.

For Men: Gradual Testosterone Decline

In men, testosterone levels also gradually decline with age. Testosterone plays an important role in maintaining muscle mass, strength and the body’s ability to build and preserve lean tissue over time. As levels decline, some men notice that maintaining muscle becomes harder than it once was, even if their exercise habits have stayed relatively similar. At the same time, fat accumulation, particularly around the abdomen, may become more common.

Because muscle is a metabolically active tissue, losing lean mass over time can gradually reduce the number of calories the body burns each day. Together, these changes can make weight gain easier and maintaining weight loss more challenging.

How to Boost Metabolism As You Age

While aging does bring real physiological changes, it does not mean weight management becomes impossible. If you’re wondering how to boost metabolism as you age, the key is to adapt your approach to work with the changes occurring in the body, not against them.

With that in mind, here are our top three tips for supporting your metabolism as you age:

Prioritise strength training

The loss of muscle mass as we age helps explain why strength training becomes increasingly important over time. Maintaining or building muscle helps preserve resting metabolic rate, supports physical function and can make weight management more manageable long term. It is one of the most effective ways to help counteract age-related muscle loss and the metabolic slowdown that can occur with age.

Importantly, strength training does not necessarily mean heavy weight-lifting workouts. Exercises that challenge the muscles consistently, including resistance bands and bodyweight exercises, can all help support muscle maintenance.

Eat enough protein

Protein becomes increasingly important with age because it directly supports the body’s ability to build and maintain muscle. As muscle mass gradually declines with age, getting enough protein becomes even more important for helping preserve muscle mass.

Protein also tends to be one of the most filling nutrients, helping support fullness and appetite control. This can make losing weight and maintaining a calorie deficit easier without feeling as hungry throughout the day.

Including a quality source of protein at all meals and snacks, such as eggs, Greek yogurt, meat, fish, tofu, legumes or dairy foods, can help maintain your metabolism and support muscle maintenance and growth.

Maintain daily movement

While structured exercise like weight training is important for maintaining muscle, overall movement across the day also plays a major role in the number of calories your body burns each day. This includes all of the energy burned outside of formal exercise through things like walking, standing, household tasks and general day-to-day movement.

This type of movement has a surprisingly large impact on total daily energy expenditure, but it’s the type of everyday movement that often declines gradually without being consciously noticed. Work may become more desk-based, free time may become more sedentary and busy schedules can leave less time and energy for general movement throughout the day.

This means that even if structured exercise stays the same, such as continuing to attend the same gym classes each week, total daily energy expenditure may still decline because overall movement across the day is lower. Over time, these small reductions in movement can reduce the number of calories the body burns each day, making weight gain gradually occur.

Finding ways to maintain or increase movement throughout the day can help support metabolism over time. Small habits like walking more, reducing prolonged sitting, taking the stairs or simply moving more regularly throughout the day can all add up and make a difference to the number of calories you burn each day.

While metabolism does change with age, many of the changes are gradual and closely linked to muscle loss and reductions in daily movement over time. Supporting muscle mass, staying active and maintaining good nutrition can all help slow this decline and make weight management more manageable as we age.

Key Takeaways

• Metabolism does change with age, but much of the shift is driven by gradual changes in muscle mass, movement and hormones.
• Losing muscle mass over time can reduce the number of calories the body burns each day, making weight gain easier even if eating habits stay relatively similar.
• Daily movement outside of formal exercise plays a major role in metabolism and small reductions in movement across the day can add up over time.
• Strength training and adequate protein become increasingly important with age because they help support muscle maintenance, metabolism and long-term weight management.
• While some metabolic changes with age are unavoidable, maintaining muscle, staying active and supporting overall nutrition can make a positive difference to your metabolism as you age.

References

1. Daily energy expenditure through the human life course (2021). doi: 10.1126/science.abe5017
2. The age-related loss of skeletal muscle mass and function: Measurement and physiology of muscle fibre atrophy and muscle fibre loss in humans (2018). doi: 10.1016/j.arr.2018.07.005