Does Metabolism Really Change With Age?

Aging, Emergency Tips, Nutrition Steward Health Care

Sure, it does. Just not when we might think.

How many of us remember when we could eat anything we wanted and not gain weight? A new study released in August 2021 now suggests that our metabolism…or the rate at which we burn calories…actually peaks much earlier and starts its inevitable decline a lot later than we all think. A recent study appeared in the Journal of Science that states that the timing of our metabolic life stages doesn’t appear to match the markers we normally associated with growing up and getting older according to the study’s co-author Jennifer Rood, Ph.D., associate executive director of Cores & Resources at Pennington Biomedical Research Center.

The 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 the participants lived in 29 different countries. In the past studies measured how much energy the body uses for basic vital functions – breathing, digesting, pumping blood, etc., the calories we need to stay alive. But basic functions account for just 50% to 70% of the calories we burn each day. In other words, they don’t include the energy we expend doing everything else – washing the dishes, walking the dog, breaking a sweat at the gym, or just even thinking and fidgeting.

To come up with the number for total daily energy expenditure the researchers turned to a “doubly labeled water method.” That’s a urine test that involves having the person drink water in which the hydrogen and oxygen in the water molecules have been replaced with naturally occurring “heavy” forms and measures how quickly they’re flushed out. Water washes out things that cause us to gain weight, but more on that later.

Pooling and analyzing energy expenditures across the entire lifestyle revealed some real surprises. Some people think of their teens and twenties as the age when their calorie burning potential hits its peak, but the recent study showed that pound for pound, infants had the highest metabolic rates of all. Energy needs shoot up during the first 12 months of life and by their first birthdays babies burn calories 50% faster for their body size than adults.

After the initial surge in infancy a person’s metabolism slows by 3% each year until our 20s when it levels off to a new normal. Now here’s the surprising thing, people’s metabolisms were most stable from their 20s through their 50s. Even calorie needs during pregnancy grew no more than expected. The findings suggest that other factors lie behind the so-called “middle age spread.” The data suggests that our metabolism doesn’t really start to decline again until after age 60. And guess what – the slowdown is gradual. Only 0.7% a year, but a person in their 90s needs 26% fewer calories each day than someone in mid-life.

Another factor is that lost muscle mass as we get older may be partially to blame researchers say. Since muscle burns more calories than fat, but that’s still not the whole picture. “We took dwindling muscle mass into account. After 60 a person’s cells slow down,” said one of the researchers.

“The findings from this research are likely to reshape the science of human physiology and it can also have implications for some medical practices, like determining appropriate drug doses for children and older people,” said Dr. Robert Watine, board certified in internal medicine and on the staff at Sebastian River Medical Center.

There are more than 80 coauthors on the study combining efforts from half a dozen labs collected over 40 years. They had sufficient information to ask general questions about changes in metabolisms over a lifetime.

“People used to think maybe it’s because we’re less active or maybe it’s because people tend to lose muscle mass as they get into their 60s, 70s and older,” said Dr. Watine, “but we can correct for all of these things. We can say no, no, no, it’s more than that. It’s that our cells are actually changing.”

What factors cause weight gain?

Registered dietitian Colleen Tewksbury, a senior research investigator at the University of Pennsylvania, and a spokesperson for the Academy of Nutrition & Dietetics, said the new study is surprising. “Historical convention was really that the different life cycle changes – puberty, pregnancy and menopause – we thought that there was some shift in metabolism, and it impacted nutrition status and how we approached things from the nutrition standpoint,” she said. “This high level, rigorous assessment does not show that. But if changing metabolism is not changing a role in weight gain at certain points in adult life, there could be other contributing factors. Tewksbury said there are lots of things that impact weight status and also sometimes nutritional status. It’s not as simple as just one food or one lifestyle or one change from a biological standpoint. It’s more likely a much more complex web of lots of different changes happening at once so that could be changes to food intake. It could be changes in activity levels. It can be where people are living, what they have access to, and what are their sleep changes.”

According to Steven Malin, an associate professor of kinesiology and health and Director of the Rutgers Applied Metabolism & Physiology Laboratory, called the study results “illuminating on something that we thought we knew a lot about and realized that there is a lot more to be discovered.” It’s not as if the weight gain is occurring because you don’t “burn the same calories anymore,” said Dr. Watine.

How do we increase our metabolism?

According to WebMD’ a lot of factors figure into increasing our metabolism. Metabolism is different for everyone. Some people have a faster one and some have a slower one, but as you age your metabolism does slow down. Metabolic rate is an umbrella term for all the chemical reactions and processes in our bodies that turn food into energy. If we use more calories than we take in, we lose weight. If we use fewer calories you may gain weight. But there’s more tour metabolism than that.

The good news is that you don’t need to live with lower metabolism after you’re 50.

A few simple life changes can help to boost it:

  • Build muscle mass. Sarcopenia, or the loss of muscle mass, speeds up after we’re 60 but metabolism, protein and muscle are connected so when muscle mass decreases so does metabolism. To boost your metabolism, try strength training and lifting weights. Building muscle mass also helps your body burn more calories so you don’t convert them to fat as easily. Weight, resistance bands, and body weight exercises can also help build muscle.
  • Get aerobic exercise. Aerobic exercise is still the key to boost our metabolism. Aerobic or cardio exercise offers the following benefits: lower blood pressure, good lung health, lower resting heart rate, helps control weight and blood sugar, lower risks of heart disease.
  • Examples of aerobic exercises are walking, swimming and water aerobics, bike riding, jogging, dancing.

Last but certainly not least…drinking water helps our metabolism. When we drink H2O our body goes through thermogenesis (body heating) to process the liquid and heat it to body temperature. This is the same process your body uses to metabolize food using energy to create heat requires burning calories and this can boost your metabolism by as much as 30%. While the process only lasts about an hour it happens each time you drink water. Staying hydrated helps when you exercise, and it helps your body dissolve important minerals and vitamins. Water helps keep skin, hair, and brain healthy.

“Last but not least,” says Dr. Watine, “Water is not just any liquid. Water is water, not flavored water, not coffee, juice, or any other liquid. This process works best with pure, clear water.”

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