You have probably heard this before. Your metabolism is slow because of your age! WRONG AGAIN! It will change if you don’t do anything about it! If anyone is physically capable of helping their activity level, why not do it?
Most of us remember a time when we could eat anything we wanted and not gain weight. But a new study suggests your metabolism, the rate at which you burn calories, actually peaks much earlier and starts its inevitable decline later than you might think. If you don’t do anything about it.
“What’s odd is that timing of our ‘metabolic life stages’ doesn’t appear to match the markers we associate with growing up and getting older,” said study co-author Jennifer Rood, Ph.D. Associate Executive Director for Cores and Resources at Pennington Biomedical Research Center.
Four Pennington Biomedical researchers were part of an international team of scientists who analyzed the average calories burned by more than 6,600 people as they went about their daily lives. The participants’ ages ranged from one week old to 95 years, and they lived in 29 different countries. The other Pennington Biomedical scientists are Peter Katzmarzyk, Ph.D., Associate Executive Director for Public Health Sciences; Coby Martin, Ph.D., Professor and Director, ingestive Behavior Laboratory; and Eric Ravussin, Ph.D., Associate Executive Director for Clinical Science.
Most previous large-scale studies measured how much energy the body uses for basic vital functions – breathing, digesting, and pumping blood — the calories you need just to stay alive. But basic functions account for just 50 percent to 70 percent of the calories we burn each day. They don’t include the energy we spend doing everything else: washing the dishes, walking the dog, breaking a sweat at the gym, even just thinking or fidgeting.
To come up with a number for total daily energy expenditure, the researchers turned to the “doubly labeled water” method. It’s a urine test that involves having a person drink water in which the hydrogen and oxygen in the water molecules have been replaced with naturally occurring “heavy” forms, and then measures how quickly they’re flushed out.
The double labelled water method is used for measuring total daily energy expenditure (TDEE) over 1-3 weeks under daily living conditions is the indicated method to study effects of exercise and extreme environments on energy balance. Subjects consume a measured amount of doubly labelled water to increase background enrichment of body water, and the subsequent difference in elimination rate as measured in urine, saliva or blood samples, is a measure for carbon dioxide production and thus allows calculation of TDEE. In untrained subjects, an exercise induced increase in activity energy expenditure is compensated by a training-induced increase an exercise efficiency.
Scientists have used the technique — considered the gold standard for measuring daily energy expenditure during normal daily life outside of the lab — to measure energy expenditure in humans since the 1980s. But previous studies were limited in size and scope due to cost. To get around the limitation, multiple labs shared their data in a single database, to see if they could tease out truths hidden or only hinted at in previous studies.
Analyzing energy expenditures across the entire lifespan revealed some surprises.
“Some people think of their teens and 20s as the age when their calorie-burning potential hits its peak.” Dr. Katzmarzyk said. “But the study shows that, pound for pound, infants had the highest metabolism rates of all.”
Energy needs shoot up during the first 12 months of life. By their first birthdays, babies burn calories 50 percent faster for their body size than adults.
And that’s not just because infants are busy tripling their birth weight in their first year.
“The babies grow rapidly, which accounts for much of the effect. However, after you control for this, their energy expenditures tend to be higher than what you would expect for their body size.” Dr. Martin said.
An infant’s explosive metabolism may help explain why children who don’t get enough to eat during this developmental stage are less likely to survive and grow up to be healthy adults.
“More research is needed to better understand the metabolism of babies. We need to know what is driving higher energy expenditures,” Dr. Martin said.
Researchers H. Shimokata and F. Kuzuya found that skeletal musculature is a fundamental organ that consumes the largest part of energy in the normal human body. The total volume of skeletal muscle can be estimated by 24-hours creatinine excretion. The volume of skeletal musculature decreases and the percentage of fat tissue increase with age. It is shown that the decrease in muscle mass relative to total body may be wholly responsible for the age related decrease in basal metabolic rate. Energy consumption by physical activity also decrease with atrophic changes of skeletal muscle. Thus energy requirement in the elderly decreases. With decrease of energy intake of essential nutrients also decrease. If energy intake, on the other hand exceeds individual energy needs, fat accumulates in the body. Body fat tends to accumulate in the abdomen in the elderly. Fat tissue in the abdominal cavity is connected directly with the liver through the portal vein. Accumulation of abdominal fat causes disturbance in glucose and lipid metabolism. It is shown that glucose tolerance, the decrease in glucose tolerance may be partly prevented through changes of life- style variables, energy metabolism is essential for the physiological functions. It may also be possible to delay the aging process of various physiological function by change of dietary habits, stopping smoking, and increase physical activity.
In terms of dietary options, calorie restriction has long been studied as a way to extend lifespan in animals. It has been associated with the ability to reduce the risks of cardiovascular and other diseases and to improve overall health. Now, researchers at Chang Gung University in Taiwan have found that calorie restriction can also be beneficial to muscles, improving muscle metabolism and mass at an important time, during middle age. The article “Late-onset Calorie Restriction Alters Skeletal Muscle Metabolism by Modulating Pyruvate Metabolism” is published ahead of print in the American Journal of Physiology-Endocrinology and Metabolism.
“To date, caloric restriction (CR) is the only non-pharmaceutical and non-genetic strategy that increases the lifespan of animals and provides health benefits.” the research team wrote. “Regarding skeletal muscle, an organ that is critical for movement and fuel metabolism, studies have reported that CR attenuates age-related muscle loss.”
Calorie restriction is thought to have a protective effect on muscle cells and may help cells better use antioxidants, avoid damage caused by free radicals and function better. While studies that observed the effects of lifelong calorie restriction have shown mixed results in animals of different ages, recent studies have suggested that age may play a role in how CR affects individual animals. The research team hypothesized that because CR can help reprogram metabolism, the most benefit can be reaped from aging muscles in which cellular metabolism is impaired.
Researchers focused on two pathways that produce energy in muscles, glycolysis (sugar metabolism) and mitochondrial oxidative phosphorylation (OXPHOS) in both young and middle-aged rats that were fed a normal diet or a calorie-restricted diet. In the 14-week study, rats on the calorie-restricted diet received 10-percent calorie restricted in the first week, 25 percent restriction in the second and 40 percent restriction for the remaining 12 weeks. The control rats received no calorie restriction. After 14 weeks, the researchers studied changes in the rats’ muscles.
“We investigated whether CR reprogrammed muscle metabolism and whether this improvement was associated with the observed increases in muscle mass. In addition, we examined whether the CR-induced changes were age-dependent.”
Not surprisingly, the middle-aged rats had less muscle mass than the young rats did. However, while 14 weeks of calorie restriction did not significantly affects the middle-aged rats, it reduced muscle mass in the young rats. Calorie restriction slowed the glycolytic rate in the muscles and increased the cells’ dependency for OXPHOS versus glycolytic rate in the muscles and increased the cells’ dependency for OXPHOS versus glycolysis in older rats, which was linked to improvement of normalized muscle mass. The team also found that “14 weeks of CR reprogrammed cellular metabolism, where the relative contribution of OXPHOS and glycolysis in muscles of middle-aged rats with CR was similar to that in muscles of young rats.”
Reference:
American Physiological Society (APS). “Caloric restriction: A fountain of youth for aging muscles?” Science Daily. 22 April 2015. www.sciencedaily.com/releases/2015/04/150422134612.htm.
Pennington Biomedical Research Center “Metabolism changes with age, just not when you might think.” Science Daily. 12 August 2021. www.sciencedaily/releases/2021/08/210812145028.htm.
