According to new research published in Science, metabolism peaks much earlier in life and slows much later than much later than we think. Before we delve into the specifics of the new research, it's necessary to establish a few terminology.
Metabolism is a term that refers to the collection of chemical process that enable an organism to live. This involves the conversion of energy from food into energy for life-sustaining processes such as breathing, circulating blood, growing and repairing cells, digesting food, and removing waste in humans.
The amount of energy required to carry out these essential processes while an organism is fasting or at rest is referred to as the basal metabolic rate, or BMR, and may be determined using a variety of online calculators that take an individual's height, weight, age, and gender into account. The term basal metabolic rate, or BMR, is frequently used interchangeably with resting metabolic rate, or RMR. Total energy expenditure (TEE) is calculated as the sum of BMR, energy used on physical activities, and energy spent on food digestion (known as dietary thermogenesis). BMR contributes for around 50% to 70% of total energy output in sedentary individuals, dietary thermogenesis accounts for 10% to 15%, and physical activity accounts for the remaining 20% to 30%.
Although we know that certain factors such as age, sex, body mass, body composition, physical activity, and illness all affect energy expenditure, the most recent comprehensive study, which included data from people worldwide, revealed surprising information about the timing of age-related metabolism changes throughout the lifespan.
Who took part in the study?
The study enrolled 6,421 participants (64 percent female) ranging in age from 8 days to 95 years from 29 nations worldwide.
What was the purpose of the study?
The researchers computed TEE in all participants using measurements of doubly labeled water (the gold standard for measuring energy expenditure). They employed additional datasets, mathematical models, and changes to account for differences in body size, age, and reproductive status. Over the life span, their studies revealed 4 different stages of adjusted total and basal energy expenditure.
What were the findings of the research?
The study describes the following phases of energy expenditure:
Neonatal (1 month to 1 year): Neonates had a similar size-adjusted energy expenditure to adults during their first month of life. Energy use grew rapidly throughout the first year, peaking at 0.7 years of age. Between the ages of 9 and 15 months, subjects' adjusted energy expenditures were nearly 50% higher than those of adults.
Childhood and adolescence (1 to 20 years): Throughout childhood and adolescence, total and basal expenditures, as well as fat-free mass, continued to increase with age, size-adjusted expenditures steadily declined. Sex had no effect on the decline's rate. TEE and RMR adjusted to adult levels hit a plateau at 20.5 years. Notably, there was no increase in adjusted total or basal energy expenditure between the ages of ten and fifteen years.
Adulthood (20 to 60 years): Total and basal metabolic expenditure, as well as fat-free mass, remained constant from 20 to 60 years, regardless of sex. Even during pregnancy, adjusted TEE and RMR remained steady, and any increase in unadjusted energy expenditure was accounted for by the rise in body mass. Age 63 was the time at which adjusted TEE began to fall, while age 46.5 was the point at which adjusted BMR began to decline (although the researchers indicate a small number of BMR measurements reduced their confidence in this estimate).
Adulthood (>60 years): Around the age of 60, TEE and BMR began to fall, as did fat-free and fat mass. However, decreases in energy expenditure exceeded what would be predicted solely from decreased body mass. TEE and BMR decreased by 0.7% per year, and adjusted total expenditure was around 26% lower in subjects 90 years old and older than in middle-aged people.
Additional findings from the study
The authors of the study were interested in the impact of physical activity and tissue-specific metabolism (the notion that certain organs, such as the brain and liver, consume more energy than others and account for a greater proportion of body weight in younger persons) across the lifetime. They determined that age-related changes in physical activity level and tissue-specific metabolism contribute to TEE at various ages; in particular, elevated tissue-specific metabolism in early life may reflect decreased energy expenditure in later life may reflect organ-level metabolic decline, whereas increased energy expenditure in early life may reflect growth or development.
What are the study's takeaways?
This finding contradicts commonly held assumptions that metabolism correlates strongly with organ-specific metabolic activity throughout children and adolescence, peaking throughout infancy, childhood, and adolescence and gradually declining during adulthood and old age. Rather than that, the authors noted that BMR was 30% higher than expected for children aged 1 to 20, and 20% lower than expected for individuals aged 60 and over. These differences in anticipated TEE and BMR in childhood and old age support the notion that age-related metabolic alterations may have a greater impact than previously recognized. Additionally, these findings clearly suggest that we may no longer be able to blame middle-age weight increase on a slowing metabolism.
What can folks do to maintain a healthy weight throughout their lives?
We must also recognise that individual differences in energy expenditure can influence a person's weight trajectory or reaction to weight-loss treatments. The findings of the study, however, do not contradict our current knowledge of how to acquire and maintain a healthy weight throughout life. The evidence is still heavily in support.
- consuming a healthy, well-balanced diet rich in nutritious foods such as fruits, vegetables, lean protein, and whole grains
- maintaining an active lifestyle with a weekly physical activity target of at least 150 minutes, including strength training to grow or maintain lean muscle mass
- obtaining enough sleep, which for most people is seven to eight hours every night
- Mindfulness, meditation, and other calming activities can help you manage stress.
