Menopause brings about significant changes in a woman's body, including shifts in energy expenditure that can affect weight management and overall health. One of the key components of daily energy expenditure is Resting Metabolic Rate (RMR), which accounts for 60-75% of the energy we use each day. RMR represents the amount of energy the body needs to maintain basic functions like breathing, circulation, and cellular processes while at rest. However, as women age, RMR tends to decline, and this reduction can accelerate during and after menopause.
Starting as early as the age of 20, a woman’s RMR begins to decline by approximately 2% per decade. This decline is influenced by several factors, including changes in hormone levels and body composition. As women transition through menopause, the decrease in estrogen levels plays a crucial role in these changes. Estrogen has been shown to have a protective effect on muscle mass and energy expenditure, so when estrogen levels drop, there's a corresponding reduction in lean body mass (muscle) and an increase in fat mass. This shift in body composition can further decrease RMR, as muscle tissue burns more calories at rest compared to fat tissue.
Predictive equations have been developed to estimate RMR based on factors like body mass, height, gender, and age. However, these equations often fall short when applied to postmenopausal women. For instance, popular equations like the Harris-Benedict and Mifflin-St Jeor were developed using data from younger populations and do not account for the hormonal changes and body composition shifts that occur during menopause. As a result, these equations can overestimate RMR, potentially leading to inaccurate recommendations for energy intake and weight management.
Menopause not only affects RMR but also influences how the body uses energy during exercise. Some studies suggest that postmenopausal women may have a lower energy expenditure during physical activity compared to premenopausal women. This reduction in energy expenditure could be due to a decrease in muscle mass, changes in fat oxidation, and reduced metabolic flexibility—the body's ability to switch between burning fat and carbohydrates for energy.
In research involving animal models, the absence of estrogen has been linked to decreased energy expenditure, both at rest and during physical activity. Similar trends have been observed in human studies, where premenopausal women with normal estrogen levels tend to burn more fat and have a higher resting energy expenditure compared to postmenopausal women.
Understanding these changes in energy expenditure is crucial for managing weight and overall health during menopause. As RMR declines, it's important to adjust calorie intake and increase physical activity to maintain a healthy weight. Strength training can help preserve muscle mass, which is vital for maintaining a higher RMR. Additionally, being mindful of the types of fats consumed—favouring unsaturated fats like those found in nuts, seeds, and fish—can support metabolic health and reduce the risk of weight gain.
The transition through menopause is accompanied by changes in energy expenditure that can challenge weight management efforts. While predictive equations can provide a rough estimate of RMR, they may not be entirely accurate for postmenopausal women. Understanding the influence of estrogen on metabolism and making appropriate lifestyle adjustments can help mitigate the effects of these changes. Maintaining a balanced diet, staying physically active, and focusing on muscle-preserving exercises are key strategies to navigate these metabolic shifts and support overall well-being during menopause.