Many of us can recall a time when food was easy and we didn't gain weight. A new study has shown that your metabolism, which is the rate at calories are burned, rises earlier than you think and begins to decline sooner than you think.These findings are published in Science."As we age there are many physiological changes that take place in different phases of our lives, such as puberty and menopause. . It is strange that our'metabolic stages' don't seem to correspond with the markers we associate growing up and getting old," Jennifer Rood PhD, study co-author and Associate Executive Director for Cores and Resources, Pennington Biomedical Research Center.The international team of scientists that analysed the daily calories consumed by over 6,600 people included four Pennington Biomedical researchers. Participants were aged from one week to 95 years old and lived in 29 countries. Other Pennington Biomedical scientists include Peter Katzmarzyk (PhD), Associate Executive Director Population and Public Health Sciences Sciences; Corby Martin (PhD), Professor and Director Ingestive Behavior Laboratory; and Eric Ravussin (PhD), Associate Executive Director Clinical Science.Large-scale studies have measured the amount of energy our bodies use to perform basic functions like breathing, digestion, and blood pumping. These are the essential calories we need just for living. Basic functions only account for 50 to 70% of calories burned each day. These calories don't account for the energy that we use to do everything else, such as washing dishes, walking the dog or going to the gym.Researchers used the "doubly-labeled water" method to calculate the daily energy expenditure. This is a urine test in which a person drinks water in which the hydrogen or oxygen has been replaced by naturally occurring "heavy" forms. Then, it measures how fast they are flushed out.AdvertisementSince the 1980s, scientists have used this technique to measure human energy expenditure. It is considered the best method for measuring daily energy consumption during daily life outside of the laboratory. However, previous studies were small and limited in scope due to costs. Multiple labs shared data to overcome this limitation.Some surprises were revealed by analyzing the energy expenditures over the whole life span and pooling them together.Dr. Katzmarzyk stated that some people view their teens and 20s the time when their calorie-burning potential reaches its peak. The study showed that infants had the highest metabolic rate of any group, pound-for-pound.During the first 12 months, energy needs increase. Babies burn calories 50 per cent faster than adults by their first birthdays.This is not because infants are constantly trying to triple their birth weight within their first year.AdvertisementThe effect is largely due to the fact that babies grow quickly. Dr. Martin explained that their energy needs are higher than you would expect given their size.The infant's rapid metabolism could explain why children who aren't able to get enough food during this stage of development may have a lower chance of surviving and growing up healthy.To better understand babies' metabolism, more research is required. Dr. Martin stated that we need to understand what drives higher energy expenditures.After an initial surge during infancy, the metabolism slows down by around 3 percent per year until your 20s when it stabilizes into a new normal.After taking body size into consideration, it was surprising that the growth spurts during adolescence did not result in an increase in daily calories. Another surprise? Another surprise? People's metabolisms were the most stable between their 20s and their 50s. Pregnancy did not require more calories than was expected.These findings indicate that there are other factors behind the so-called middle-age spread.Data suggests that metabolism doesn't start to decline after 60. This slowdown is only 0.7 percent per year. However, a person in their late 90s requires 26 percent less calories per day than someone in their midlife.Researchers believe that losing muscle mass may partly be to blame as we age, because muscle burns more calories per calorie than fat. However, it is not the only problem."We also took into consideration the dwindling muscles mass. Dr. Ravussin stated that after 60, cells in a person's body slow down."Even when different activity levels were considered, the patterns held.It is difficult to understand why energy expenditure shifts occur when there are so many physiological changes associated with aging. The new research suggests that this is more than just age-related changes in lifestyle and body composition."This study shows how the work cells change over time in ways that we didn't understand before. Dr. Ravussin stated that large data sets such as the one that we shared allow us to address questions we didn't know were possible.This research was funded by the United States National Science Foundation (BCS-1824466) and the International Atomic Energy Agency (Taiyo Nippon Sanso, SERCON).
