According to new research published in the journal Science, metabolism peaks far earlier in life and slows much later than previously assumed. Let's establish a few concepts before getting into the specifics of the new study. 

Metabolism refers to the collection of chemical reactions that allow an organism to live. This involves the conversion of food energy into energy for life-sustaining processes like breathing, circulating blood, growing and repairing cells, digesting food, and removing waste in humans. The basal metabolic rate, or BMR, is the amount of energy required to carry out these essential functions while an organism is fasting and at rest. Resting metabolic rate, or RMR is another term for BMR. Total energy expenditure (TEE) is the sum of BMR, energy expended on physical activity, and energy expended on digestion (known as dietary thermogenesis). BMR contributes for roughly 50% to 70% of total energy output in sedentary adults, dietary thermogenesis accounts for 10% to 15%, and physical activity accounts for the remaining 20% to 30%. We know that age, sex, body mass, body composition, physical activity, and disease all affect energy expenditure, but the most recent comprehensive study, which included data from people all over the world, uncovered interesting information on the timing of age-related metabolic changes across time. 

Who was involved in the research?  

The study included 6,421 individuals (64 percent female) ranging in age from 8 days to 95 years old from 29 countries throughout the world.  

What was the purpose of the research?  

TEE was estimated in all participants using water measures that were twice labeled (the gold standard for measuring energy expenditure). To account for disparities in body size, age, and reproductive status, they used additional datasets, mathematical models, and adjustments. Throughout a lifetime, they discovered four unique periods 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): In the first month of life, neonates had equivalent size-adjusted energy expenditure to adults. Over the first year, energy expenditure climbed rapidly, peaking at 0.7 years old. The adjusted energy expenditures of subjects aged 9 to 15 months were about 50% higher than those of adults.  

-Childhood and adolescence (1 to 20 years): While total and basal expenditures, as well as fat-free mass, increased with age throughout childhood and adolescence, size-adjusted expenditures decreased steadily. Sex had no bearing on the outcome. TEE and RMR adjusted to adult levels hit a plateau at 20.5 years. During the pubertal years of 10 to 15, there was no rise in adjusted total or basal energy expenditure.  

-Adulthood (20-60 years): Total and basal expenditure, as well as fat-free mass, remained constant from 20 to 60 years old, regardless of gender. Even during pregnancy, adjusted TEE and RMR remained steady, and an increase in unadjusted energy expenditure was accounted for by the rise in body mass. Adjusted TEE began to fall at age 63, while adjusted BMR began to decline at age 46.5 (although the researchers note that a small number of BMR measures reduced their confidence). 

-TEE and BMR, as well as fat-free mass and fat mass, began to fall at the age of 60. Energy expenditure decreases, on the other hand, were more than would be expected from a reduction in body mass alone. TEE and BMR decreased by 0.7 percent each year, and adjusted total expenditure was around 26% lower in patients 90 years and older than in middle-aged adults.  

Additional findings from the research  

Physical activity and tissue-specific metabolism (the assumption that some organs, such as the brain and liver, utilize more energy than others and account for a higher percentage of body weight in younger people) were studied over the lifetime by the researchers. They discovered that age-related changes in physical activity level and tissue-specific metabolism contribute to TEE at various ages, with elevated tissue-specific metabolism in early life possibly related to growth or development, and reduced energy expenditure in later life possibly reflecting organ-level metabolic decline, using various modeling scenarios.  

What are the key takeaways from this research?  

This research casts doubt on long-held assumptions that metabolism is tightly linked to organ-specific metabolic activity throughout growth and development, peaking in infancy, childhood, and adolescence before gradually declining into adulthood and old age. Instead, the authors discovered that BMR in children 1 to 20 years old was 30% higher than expected based on body and organ composition, and 20% lower than expected in seniors 60 and older. These differences in anticipated TEE and BMR in childhood and old age support the idea that age-related metabolic alterations play a bigger role than we previously thought. Furthermore, these findings strongly suggest that a slowing metabolism may no longer be the cause of weight increase in middle age.  

What can folks do to maintain a healthy weight throughout their lives?  

We must also recognize that individual differences in energy expenditure can have an impact on a person's weight. 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 overwhelmingly in favor.  

• 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 goal of at least 150 minutes of physical activity, including -strength training to increase or maintain lean muscle mass getting enough sleep, which for most -people is seven to eight hours per night managing stress through mindfulness, meditation, or other relaxing activities