🤩 Research debunks old wisdom on Metabolism 🤩
Metabolism studies have revealed surprising insights into how we burn calories! Should we eat that cake?
For all the talk about metabolism in the exercise and dieting worlds, you would think the science was settled. In reality, we've been embarrassingly short on hard data about the calories we burn each day.
But recently research has made important strides in understanding how our bodies use energy. The findings have overturned much of the perceived wisdom about the ways human energy requirements change over the course of a lifetime.
Today, I’ll share with you the new research and the good news; providing the clearest picture yet of the inner workings of the human engine - and how our strategy for burning calories underpins our extraordinary success as a species.
Before we get started, if you missed last week’s blog on“The best habits of Sex-cessful couples”, you can use this link, Here.
OK, ready to find out what the latest research says about metabolism?
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ENERGY BUDGETS
Our bodies are wonders of coordinated chaos. Every second of every day, each of your 37 trillion cells is hard at work, pulling in nutrients, building new proteins and doing the myriad other tasks that keep you alive. All of this work takes energy. Our metabolism is the energy we expend (or the calories we burn) each day. That energy comes from the food we eat, and so our metabolism also sets our energy requirements. Calories in, calories out.
Biologists often think about metabolism as an organism's energy budget. Life's essential tasks, including growth, reproduction and bodily maintenance, require energy. And every organism must balance its books.
Humans are a striking example of this evolutionary bookkeeping in action. The traits that distinguish us from the other apes, including our huge brains, big babies and long lives, all require a lot of energy. We pay for some of these costs by spending less on our digestive system, having evolved a shorter intestinal tract and smaller liver. But we have also increased our metabolic rate and the size of our energy budget. For our body size, humans consume and burn more calories each day than any of the other apes. Our cells have evolved to work harder.
The work our bodies do changes as we age, the activities of our cells waxing and waning in a choreographed dance from growth to adulthood to senescence. Tracking those changes through our metabolism can provide a better understanding of the work our cells do at each age as well as our changing calorie needs. But a clear audit of our metabolism over the human life span has been hard to obtain.
It's obvious that adults need more calories than infants - bigger people have more cells doing more work, so they burn more energy. We also know that elderly people tend to eat less, although that's often accompanied by a loss of body weight, particularly muscle mass. But if we want to know how active our cells are and whether metabolism gets faster or slower as we grow up and grow old, we need to separate the effects of age and size, which is not easy. You need a large sample with people of all ages, measured with the same methods. Ideally, you'd want measures of total daily energy expenditure, a full tally of the calories used each day.
Researchers have been measuring metabolic rates at rest for more than a century, with some evidence for faster metabolism in children and slower metabolism among the elderly. Yet resting metabolism accounts for only 60 percent or so of the calories we burn over 24 hours and doesn't include the energy we spend on exercise and other physical activity.
Online calorie calculators purport to include activity costs, but they're really just a guess based on your self-reported weight and physical activity. In the absence of solid evidence, a kind of folk wisdom has developed, cheered on and cultivated by charismatic hucksters selling metabolic boosters and other snake oil.
We're often told our metabolism speeds up at puberty and slows down in middle age, particularly with menopause, and that men have faster metabolisms than women. None of these claims is based on real science.
A METABOLIC DATABASE
In 2014 researchers in metabolism, organized an international effort to develop a large metabolic database. They ended up with more than 6,400 measurements of people ranging from babies just eight days old to men and women in their 90s.
In 2021, after years of collaborative effort, the research was published showing the first comprehensive study investigating the effects of age and body size on daily energy expenditure. As expected, it was found that metabolic rates increase with body size: bigger people burn more calories. In particular, fat-free mass (the muscles and other organs) is the single strongest predictor of daily energy expenditure.
This makes good sense. Fat cells aren't as active as those in the liver, brain, or other tissues, and they don't contribute much to your daily expenditure. More important, with the relation between mass and metabolic rate clearly established from thousands of measurements, they could finally test whether metabolism at each age was faster or slower than we'd expect from size.
The results were a revelation, the first clear road map of metabolism over the human life span. The research found that, metabolically, babies are born like tiny adults, reflecting their development as part of their mom's energy budget. But metabolism skyrockets over the first year of life, so that by their first birthday children are burning 50 percent more energy than we'd expect for their size. Their cells are far busier than adults' cells, hard at work on growth and development.
Metabolism stays elevated through childhood, slowly decelerating through adolescence to land at adult levels around age 20. Boys decline more slowly than girls, consistent with boys' slower development, but there's no bump at puberty in males or females.
Perhaps the biggest surprise was the stability of our metabolism through middle age. Daily energy expenditures hold remarkably steady from age 20 to 60. No middle age slowdown, no change with menopause.
The weight gain so many of us experience in adulthood cannot be blamed on a declining metabolism. As a middle-aged man, I had sort of believed the folk wisdom that metabolism slowed as we aged. My body definitely feels different than it did 10 or 20 years ago.
Same for the much touted metabolic differences between men and women. Women have lower daily energy expenditures on average, but that is only because women tend to be smaller and carry more of their weight as fat. Compare men and women with the same body weight and body fat percentage, and the metabolic difference disappears.
Research did find a decline in metabolism with age, but it doesn't kick in until we hit 60. After 60, metabolism slows by around 7 percent per decade. By the time men and women are in their 90s, their daily expenditures are 20 to 25 percent lower, on average, than those of adults in their 50s. That's after accounting for body size and composition.
Weight loss with old age, especially diminished muscle mass, compounds the decline in expenditure. As with all age groups, there's a good amount of individual variability. Maintaining a younger, faster metabolism into old age might be a sign of aging well, or perhaps it is even protective against heart disease, dementia and other age-related disease.
WHAT ABOUT EATING THAT CAKE?
What is already apparent, however, is that a bite of birthday cake does different things for a seven-year-old girl, her middle-aged dad and her elderly grandmother. A preschooler's bite is likely to be gobbled up by busy cells, fueling development. A 40 year old’s bite of cake might go to maintenance, repairing all the little bits of damage accrued through the course of the day. As for Grandma, her aging cells might be slow to use the calories at all, storing them instead as glycogen or fat. Indeed, for any of us, the cake will end up as fat if we eat more calories than we burn.
Maybe trying a smaller piece or a healthier treat (dark chocolate square, fruit, nuts) would be the better option for all of us. No one benefits from stored fat or the impending sugar rush speeding us towards hyperglycaemia.
Chances are you've experienced a sugar rush – that euphoric, energeticfeeling you have after eating certain foods – and the dreaded crash that follows. While the initial bite of a favorite snack may bring joy, the potential health impacts aren't so thrilling.
THE BOTTOM LINE
“You can dramatically affect the expression of your metabolism and your biochemistry by the way you eat and the way you live.”
“Give up sugar, stevia, aspartame, sucralose, sugar alcohols like xylitol and malitol, and all of the other heavily-used and marketed sweeteners unless you want to slow down your metabolism, gain weight, and become an addict.”
“All those spices and herbs in your spice rack can do more than provide calorie-free, natural flavorings to enhance and make food delicious. They're also an incredible source of antioxidants and help rev up your metabolism and improve your health at the same time.”
“The cakes and pains of old age.”
We're often told our metabolism speeds up at puberty and slows down in middle age, particularly with menopause, and that men have faster metabolisms than women. None of these claims is based on real science.
In short, after investigating the effects of age, body composition, and sex , new research has found that total expenditure and its components, varies as we age, with four distinct metabolic life stages reflecting changes in behavior, anatomy, and tissue metabolism.
Metabolism stays elevated through childhood, slowly decelerating through adolescence to land at adult levels around age 20. Boys decline more slowly than girls, consistent with boys' slower development, but there's no bump at puberty in males or females.
Perhaps the biggest surprise was the stability of our metabolism through middle age. Daily energy expenditures hold remarkably steady from age 20 to 60. No middle age slowdown, no change with menopause.
Women have lower daily energy expenditures on average, but that is only because women tend to be smaller and carry more of their weight as fat. Compare men and women with the same body weight and body fat percentage, and the metabolic difference disappears.
Research did find a decline in metabolism with age, but it doesn't kick in until we hit 60. After 60, metabolism slows by around 7 percent per decade. By the time men and women are in their 90s, their daily expenditures are 20 to 25 percent lower, on average, than those of adults in their 50s. That's after accounting for body size and composition.
Hopefully these new findings will give you added hope if you are just now working on your best self and helping your body overcome past years of neglect. To read the full PubMed research text, click Here.
Make an appointment and come talk with us if you are having doubts or questions about your family’s health. We will give you the honest truth, and the clinical research that supports it.
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