The Truth About Metabolism: What You Need to Know

As we age, our metabolism changes – we gain weight and lose energy. We will explain why metabolism slows down with age and how to keep your metabolic rate healthy.

Metabolism is the sum of all the chemical processes in your body to digest and absorb nutrients from food to sustain life.

This complex system includes total energy expenditure (TEE), the sum of basal metabolic rate (BMR), energy used for physical activities, and energy used to digest food.

Total daily energy expenditure (TDEE) is the total calories your body uses daily and is influenced by body composition.

Metabolism follows a specific pattern throughout our lives:

So, for most of our adult life, our metabolic rate is stable, not declining from early adulthood, as we are often told.

However, age-related changes in physical activity, tissue-specific metabolism, and body size impact total energy expenditure at different life stages.

In early life, tissue-specific metabolism is higher, so energy needs are higher; in later life, metabolism is slower so energy expenditure is lower,.

To support metabolic health throughout the human life course, we need to understand these changes.

Natural loss of muscle mass, which can start as early as 30, is one of the main reasons metabolism slows down with age.

This process is called sarcopenia and can result in a 3-5% loss of muscle mass per decade.

By 40, this muscle loss accelerates and is replaced by fat, further slowing it down.

A slow metabolism occurs when you burn fewer calories at rest because of the loss of muscle mass.

Decreased physical activity also plays a big role. Older adults are less active, contributing to muscle loss and directly affecting the number of calories burned through physical activity.

Muscle loss and reduced activity result in lower metabolic rate and energy expenditure. Hormonal changes, such as lower testosterone and estrogen levels, also worsen this decline.

While genetics play a role in muscle size and the ability to build muscle, their impact on metabolism is smaller than that of lifestyle factors.

Changes in sodium-potassium pumps and mitochondria are present but have a minimal effect on overall metabolism compared to muscle loss and reduced physical activity.

A higher metabolism is mainly due to the role of muscle mass.

More muscle mass means a higher metabolic rate, as muscles require more energy than fat.

That’s why strength training and other muscle-building activities are key to boosting metabolism and burning more calories at rest.

As we age, preserving muscle mass for both men and women cannot be emphasized enough.

Preserving muscle mass has many benefits.

It prevents weight gain, supports overall metabolic health, improves balance, reduces the risk of falls, and helps maintain mobility.

Focusing on muscle health and fat-free mass can reverse many of the declines in metabolism and energy expenditure that occur as we age.

For women, menopause leads to lower estrogen hormone levels, which can slow down metabolism and lead to weight gain.

Men experience a decline in testosterone levels, which also affects muscle mass and body composition changes, which impact metabolic rate.

The thyroid gland, which produces hormones that regulate metabolism, may become less efficient with age.

The adrenal cortex hormone aldosterone, which helps maintain fluid and electrolyte balance, also decreases with age.

Although cortisol levels in the blood do not decrease, they can still impact metabolic health by influencing appetite and fat storage.

Stress and sleep quality are also key factors.

Chronic stress triggers cortisol release, which can increase appetite, promote fat storage, and negatively impact metabolism.

Poor sleep quality disrupts hormonal balance and contributes to metabolic decline.

Addressing these hormonal changes through lifestyle changes can help maintain a healthy metabolism.

Adequate protein intake is crucial for preserving muscle mass and preventing metabolic decline.

Protein-rich foods have a higher thermogenic effect, meaning they require more energy to digest, which can help boost metabolism.

Besides protein, whole grains play a big role.

They are rich in fiber and nutrients, which help regulate blood sugar levels and support essential functions.

Additionally, avoid late-night eating as it can increase hunger signals, decrease leptin levels, and slow down calorie burn.

By incorporating these dietary strategies, you can have a stable and efficient metabolism.

Exercises like high-intensity interval training (HIIT) are particularly effective in boosting metabolism.

Moderate physical activity is also important for older adults to manage obesity, heart disease, and diabetes.

By keeping active, you can maintain a healthy weight, preserve muscle mass, and support overall metabolic health.

Metabolism is greatly affected by several lifestyle factors, including age, gender, sleep, and stress management.

Non-exercise activity thermogenesis (NEAT), which includes calories burned through activities other than exercise or resistance training, accounts for a large portion of daily energy expenditure.

Older adults burn 29% fewer calories through NEAT, so they may need to adjust their activity level or calorie intake.

There are several myths about aging and metabolism. One is that weight gain is inevitable with age.

While most adults gain 1-2 pounds yearly from 40 to 65, it doesn’t mean weight gain is unavoidable.

Hormones play a role in this as well, so it's good to have them checked.

Another myth is that metabolism slows down uniformly across all ages.

However, a study on women of all ages found no significant difference in resting metabolic rate (RMR) among different age groups; thus, metabolism doesn’t slow down equally.

Restrictive diets, such as calorie-restricted diets, can also slow down metabolism, telling the body to conserve energy by slowing down the metabolic process.

Understanding individual variation in energy expenditure is key to achieving and maintaining a healthy weight throughout life.

Exercising regularly, strength training, and adequate protein intake are essential to maintaining a healthy metabolism.

Staying hydrated, getting enough sleep, adjusting eating habits, and staying physically active can also help seniors maintain a healthy weight and prevent metabolic decline.

Adding green tea to your diet can boost metabolism due to its caffeine and plant compounds.

Drinking green tea can increase metabolism by 4-5%, making it a simple and effective addition to a healthy lifestyle.