Experts Debunk Metabolism Myth, Explain Why Weight Loss Gets Harder with Age

The common belief that metabolism significantly slows down with age, making weight loss increasingly difficult, is largely a myth, according to recent scientific evidence. A 2021 study published in the journal Science concluded that energy expenditure remains relatively consistent between the ages of 20 and 60. However, experts explain that several other factors contribute to the perception and reality of weight gain becoming more challenging as people age.

In one's twenties, individuals typically have a higher proportion of muscle mass and lower body fat. Muscle tissue is metabolically active and requires more energy to maintain compared to fat. This higher muscle-to-fat ratio means a greater resting metabolic rate, allowing for more calorie consumption without leading to significant fat storage. Additionally, younger adults often have higher activity levels, engaging in more physical movement throughout the day, whether through exercise, commuting, or social activities. This combination of higher muscle mass and greater overall activity makes it easier to manage weight.

Experts note a shift around the age of 35. From this point onward, adults begin to lose muscle mass at a rate of about one percent per year, unless engaging in strength training. This decline in metabolically active tissue can lead to a decrease in the calories burned at rest. Concurrently, sedentary behavior often increases. A 2018 study tracking individuals between 38 and 50 found that sedentary time rose by approximately 40 minutes per day, while light physical activity decreased by half an hour daily. Factors such as longer working hours, increased family responsibilities, and subtle changes in eating habits, like consuming children's leftovers, can contribute to a small calorie surplus that accumulates over time.

For women, hormonal changes associated with perimenopause and menopause can also influence weight distribution. A decline in estrogen can lead to an accumulation of fat around the abdomen rather than the hips and thighs. While this visceral fat may respond to calorie restriction, its internal location can make changes less visible externally. Sleep disturbances due to hot flashes can also elevate cortisol levels, potentially increasing hunger hormones.

As individuals enter their sixties and beyond, a phenomenon known as anabolic resistance affects aging muscle, making it less responsive to protein for repair and growth. This accelerates muscle mass loss. While the overall calorie needs may not drastically change, the requirement for protein increases to help preserve muscle mass and maintain mobility. Experts suggest older adults aim for 1.0–1.2 grams of protein per kilogram of body weight daily, compared to the general adult recommendation of 0.8 g/kg. Maintaining adequate energy and protein intake is crucial for preserving strength and independence in later life, with recommendations suggesting around 30 calories per kilogram of body weight per day.