Understanding Why Resting Energy Decrease Over Time

November 25, 2025 •

4 min read

Studies have shown that resting energy expenditure (REE) can decrease by 1–2% per decade after the age of 30, highlighting a natural metabolic change that causes resting energy decrease over time. Understanding the factors behind this decline is crucial for managing weight and maintaining overall health as you age.

Quick Summary

This article explores the primary reasons for a decrease in resting energy, including age-related muscle loss, prolonged calorie restriction, and hormonal imbalances. We cover the physiological mechanisms and offer actionable strategies to support a healthier metabolic rate.

Key Points

Age and Sarcopenia: As we get older, a natural loss of muscle mass (sarcopenia) leads to a lower resting energy expenditure, as muscle is more metabolically active than fat.
Calorie Restriction: Severe or prolonged calorie restriction can trigger adaptive thermogenesis, where the body slows down its metabolism to conserve energy, making weight loss more challenging.
Sedentary Lifestyle: A lack of physical activity, especially resistance training, directly reduces muscle mass and overall calorie burn, contributing to a lower REE.
Hormonal Health: Conditions like hypothyroidism (underactive thyroid) are a primary cause of a decrease in resting metabolic rate due to lower thyroid hormone production.
Quality Sleep: Poor and insufficient sleep can disrupt circadian rhythms and negatively impact your metabolism, contributing to a slower resting energy burn.
Protein Intake: Ensuring adequate dietary protein helps minimize the drop in REE during weight loss, as protein has a higher thermic effect than fats or carbohydrates.
Proactive Management: Incorporating strength training, prioritizing sleep, and eating a balanced diet are key strategies for mitigating a decrease in resting energy and supporting overall metabolic health.

The Fundamentals of Resting Energy

Resting Energy Expenditure (REE), often used interchangeably with Basal Metabolic Rate (BMR), represents the number of calories your body burns at complete rest to perform essential life-sustaining functions. This includes breathing, circulating blood, and regulating body temperature. REE accounts for the largest portion of your total daily energy expenditure (TDEE), making it a significant factor in weight management.

Several factors influence your REE, with some of the most critical being body composition, age, and hormonal status. A decrease in REE, for many, is an unwelcome development that can make weight loss difficult and weight gain more likely. However, by addressing the root causes, it's possible to mitigate the impact of a slower metabolism.

Key Reasons Why Resting Energy Decrease

Age-Related Changes: Sarcopenia and Organ Metabolism

As we get older, our bodies undergo a shift in composition. There is a natural tendency to lose lean muscle mass, a condition known as sarcopenia. Muscle is a more metabolically active tissue than fat, requiring more calories to maintain, even at rest. Therefore, as muscle mass declines and fat mass increases, resting energy expenditure naturally decreases. This shift often begins in the fourth decade of life and can be accelerated by a sedentary lifestyle. Research has also shown that a smaller intrinsic loss of REE may be due to a decline in specific organ and tissue metabolic rates with aging, though the loss of fat-free mass is the most significant contributor.

The Impact of Diet and Calorie Restriction

When you significantly reduce your calorie intake for a prolonged period, your body's survival instincts kick in. It perceives a state of starvation and conserves energy by lowering your metabolic rate. This phenomenon is called adaptive thermogenesis. This can make it incredibly challenging to continue losing weight or to keep lost weight off, as your body becomes more efficient at using fewer calories. The metabolic slowdown can persist even after the diet has ended, which is a major factor in weight regain. It is important to approach calorie deficits carefully and not drastically drop below certain thresholds to minimize this adaptive response.

Sedentary Lifestyle and Lack of Physical Activity

A lack of regular physical activity directly contributes to a lower REE. Consistent exercise, particularly strength training, builds and maintains muscle mass, which helps keep your metabolism humming. Conversely, a sedentary lifestyle promotes the loss of this metabolically active tissue, leading to a decreased resting energy output. Even non-exercise activity thermogenesis (NEAT), the energy expended for everything other than sleeping, eating, or sports-like exercise, plays a role. Those with low NEAT, such as individuals with desk jobs, burn significantly fewer calories throughout the day. The good news is that resistance training can increase your REE, providing a lasting metabolic boost.

Hormonal Imbalances: The Thyroid Connection

Your thyroid gland plays a crucial role in regulating your metabolism by releasing hormones that control the rate at which your body converts oxygen and nutrients into energy. An underactive thyroid, or hypothyroidism, leads to a decrease in the production of these hormones, causing a significant metabolic slowdown. This can result in weight gain, fatigue, and other symptoms. In addition to the thyroid, other hormonal shifts can also impact REE:

Testosterone levels naturally decline with age in both men and women, and this drop can contribute to muscle loss and a slower metabolism.
The appetite-regulating hormone leptin is also known to have a positive correlation with REE, and changes in its levels can affect energy expenditure.

Poor Sleep Quality

Rest and recovery are vital for metabolic function. Numerous studies have linked poor sleep quality and insufficient sleep duration to a lower metabolic rate. This is believed to be due to disruptions in the body's natural circadian rhythms. Prolonged sleep restriction can significantly decrease resting metabolic rate, compounding other factors that cause a decline in energy expenditure. Prioritizing 7-9 hours of quality sleep per night is an important, often overlooked, strategy for maintaining a healthy REE.

Comparison Table: Factors That Influence Resting Energy


Factor	Effect on Resting Energy	Why it Changes REE	How to Counteract the Effect
Age	Decreases	Loss of muscle mass (sarcopenia) and potential changes in organ metabolism	Engage in regular strength training and maintain an active lifestyle
Weight Loss	Decreases (adaptive)	The body conserves energy in response to reduced calorie intake	Avoid overly restrictive 'crash diets' and implement a moderate, balanced approach
Muscle Mass	Increases	Muscle tissue is more metabolically active and burns more calories at rest	Incorporate resistance and weight training to build and preserve muscle
Hormonal Health	Decreases (e.g., hypothyroidism)	Underactive thyroid gland and declining levels of hormones like testosterone	Manage any underlying conditions with a healthcare provider and maintain a healthy weight
Sleep Quality	Decreases	Inadequate sleep and disrupted circadian rhythms negatively impact metabolism	Prioritize consistent sleep duration and quality, aiming for 7-9 hours per night
Dietary Protein	Increases	Protein requires more energy to digest than carbohydrates or fats (higher thermic effect)	Ensure adequate protein intake, especially during weight loss, to minimize metabolic slowdown
Sedentary Lifestyle	Decreases	Lack of activity leads to lower overall energy expenditure and muscle loss	Increase both structured exercise and non-exercise activity (NEAT)

Conclusion: Taking Control of Your Metabolism

A decrease in resting energy expenditure is a common concern, but it is not an irreversible fate. Many of the contributing factors are within our control. By focusing on building and maintaining muscle mass through strength training, prioritizing quality sleep, and approaching diet in a balanced, sustainable way, you can support your metabolic health. Addressing underlying hormonal issues with professional guidance is also an essential step. Taking a proactive approach can help you manage your weight and feel more energetic, regardless of age. For more information on strategies for healthy aging and metabolism, consider consulting resources from trusted health organizations like the Mayo Clinic.

Frequently Asked Questions

REE is the number of calories burned at rest under normal conditions, while BMR is measured under stricter, more controlled conditions (e.g., in a dark room after a 12-hour fast). For most practical purposes, the terms are used interchangeably, but REE is slightly higher than BMR.

A slower resting metabolism means your body burns fewer calories at rest, which can make it easier to gain weight if your calorie intake is not adjusted accordingly. However, it does not guarantee weight gain; managing diet and physical activity remains key.

On average, resting energy expenditure can decrease by 1–2% per decade after the age of 30. This decline is primarily driven by age-related muscle loss and changes in body composition.

Yes, you can. The most effective way is to build and maintain muscle mass through regular resistance training. Muscle tissue is more metabolically active, meaning it burns more calories at rest than fat tissue.

During a diet with significant calorie restriction, the body reduces its REE to conserve energy, a process called adaptive thermogenesis. This can slow down weight loss and increase the likelihood of regaining weight later.

Poor sleep quality and duration can lower your resting metabolic rate and disrupt circadian rhythms, negatively impacting your body's energy regulation. Prioritizing 7-9 hours of restful sleep per night is crucial for metabolic health.

Yes, certain conditions can affect your REE. Hypothyroidism, an underactive thyroid gland, is a well-known cause of a reduced metabolic rate. Other chronic illnesses or hormonal imbalances can also play a role.

It is challenging to prevent an adaptive decrease in REE during weight loss, but you can minimize it. Strategies include avoiding severe calorie restriction, ensuring adequate protein intake, and incorporating regular strength training into your routine.

A sedentary lifestyle leads to a gradual loss of muscle mass, which is a primary driver of a lower REE. A lack of movement also decreases non-exercise activity thermogenesis (NEAT), reducing your overall daily calorie burn.