Seemingly unexplainable and stubborn weight gain is a common complaint amongst middle age populations. It is estimated that the average American will gain 30 pounds by the age of 50 or about 1-2 pounds per year. It has long been believed that the main driver for this weight gain is caused by a slowing metabolism, however emerging research suggests that metabolism itself may not be to blame.
Researchers analyzed data from a diverse database of over 6,000 people aged 8 days to 95 years. Findings published in the journal Science revealed that our metabolism peaks during infancy and begins to slow through our childhood and late adolescence. By the time we are 20 years old, our metabolism has slowed by approximately 3% each year.
"...energy expenditure actually decreases after the first year of life."
Although these early years are often associated with an increased metabolism and the seeming ability to consume just about anything without weight gain, these findings suggest energy expenditure actually decreases after the first year of life.
More interestingly, researchers found that metabolism remains exceptionally steady from the age of 20 to 60, and only after 60 does it begin to slow. The metabolism of adults older than 90 is approximately “26% below that of middle-aged adults.”
This emerging evidence contradicts what many have been led to believe about metabolism and energy expenditure, and prompts further questioning into why adults tend to gain weight if not for a slowing metabolic rate.
"A body composition made up of more muscle and less fat contributes to a higher metabolic rate and energy expenditure."
One likely explanation is the propensity for adults to lose muscle mass as they age, also known as sarcopenia. Muscle is more metabolically active than fat, which means muscle burns more calories at rest. A body composition made up of more muscle and less fat contributes to a higher metabolic rate and energy expenditure.
While sarcopenia is thought to be a natural aging process, inactivity and an unhealthy diet can contribute to excessive muscle loss. In order to prevent the loss of muscle and replacement by intramuscular fat and consequent decline in metabolism, engage in regular exercise that includes strength training and prioritize a balanced diet with adequate amounts of protein.
"...metabolism may slow as we age, but likely not at the rate in which we have been led to believe."
In summary, metabolism may slow as we age, but likely not at the rate in which we have been led to believe. Gaining weight in the form of fat may contribute to a slower metabolism rather than a slower metabolism contributing to weight gain.
Additionally, the slowing of the metabolism is likely influenced by common lifestyle habits in middle age and adulthood such as a more sedentary life and a poor diet as well as increased stress and inadequate sleep. As discussed many times previously in the Mind Gut Connection newsletter, maintaining an active lifestyle, eating a balanced diet, managing stress and getting enough sleep can help to promote optimal health and longevity.