Many Americans worry about the extra pounds they gained during the pandemic. But if you believe your sluggish middle-aged metabolism contributed to your weight gain, it’s time to rethink.
Researchers who conducted a study recently published in Science have come up with new and surprising insights into how metabolism actually works in old age.
“Our paper provides the first life-span metabolism roadmap,” said study co-researcher Herman Pontzer, professor of evolutionary anthropology at Duke University in Durham, NC, and author of the book Burn, which is about metabolism and health. “Metabolism is incredibly stable between the ages of 20 and 60, although it is widely believed that our metabolism slows down as we age.”
Let’s take a look at how the researchers came to their conclusions and what it means to strive to maintain a healthy weight for a lifetime.
Metabolism is the process your body uses to break down food and turn it into energy. Previous studies of metabolism and aging failed to provide a clear understanding of how the two related because their sample sizes weren’t large enough, and that’s because of the cost of the best way to measure energy use, known as the double-labeled water technique.
In order to overcome the hurdle of costly research, more than 80 co-authors have bundled 40 years of studies for this report. Data from more than 6,400 participants, ages 8 days to 95 years, provided a wide-angle view of metabolism over many years, and the researchers found that changes in metabolic rate over life span were greater than expected.
According to the new study, the metabolism can be divided into four different life stages: At the age of 1 year, energy consumption quickly increases to 50% above the adult value; slowly declines to adult level at the age of 20; remains stable between the ages of 20 and 60; and decreases steadily after the age of 60.
“We knew in the study that body size, especially lean mass, would be the biggest factor influencing the calories burned daily: taller people burn more energy,” said Pontzer. “Our study was able to show the relationship with size very clearly and then ask new questions: How do age and gender affect metabolism if we take size and fat percentage into account?”
The discovery that the metabolism slows down after the age of 60 and not only after the age of 30 or 40 came as a surprise to the researchers, as was the difference between men and women. Men have long been believed to have “faster metabolisms” than women, but Pontzer says the theory hasn’t really been backed by research.
“Men, on average, burn more calories a day than women, but only because men tend to be taller and have slightly less body fat,” said Pontzer. “Once you have these differences under control, your metabolism will be the same. A man and a woman with the same body weight and fat percentage have the same expected metabolic rate. “
At this point, many of you may remember the mid-life weight gained and think, “This study is wrong!” And maybe after the age of 40 you gained weight. But this study suggests that this was due to reasons outside of metabolism, perhaps a change in lifestyle, diet, exercise level or hormones, or a medical condition.
Or, you might be an outlier in the population-based results. The researchers’ data showed that some people had a metabolic rate of 25% below or above the average of their age. But these outliers did not change the overall pattern of metabolic rates over the life span.
If you’ve spent years buying metabolism-boosting supplements like cayenne pepper, caffeine, and green tea, you are wasting your money. “Our work supports the view that our metabolism is difficult to shake: our bodies follow a programmed course for life, and there is not much we can do to change our daily energy consumption,” says Pontzer.
Catherine M. Champagne, professor of nutritional epidemiology at Pennington Biomedical Research Center at Louisiana State University-Baton Rouge, said there is “insufficient research on nutritional supplements that boost metabolism. The evidence for supplements like green tea or cayenne pepper comes from anecdotal advertising – not from evidence-based research. “
Champagne explains that products like caffeine and ephedrine – which are touted for metabolism boosting and weight loss – can negatively impact metabolism and are potentially dangerous for some.
Does exercise help boost the metabolism? It can help a little. Yoni Freedhoff, associate professor of family medicine at the University of Ottawa and medical director of the Bariatric Medical Institute in Ottawa, said that weight training that increases muscle mass can boost your metabolism, but he adds that the increase isn’t dramatic. He also said, “We decondition quickly when injuries or lives get in our way.”
I wasn’t surprised to learn that slow metabolism is not a major cause of midlife weight gain. In my 22 years as a nutritionist, I’ve learned how complex weight management can be, and I know that many different factors can cause obesity. The calorie-in-calorie-out theory (you lose weight if you eat fewer calories than you burn) is always important, but it’s not the whole story of weight management. It doesn’t take into account how different foods affect your hormones, nutritional needs, and satiety levels.
“Studies have shown that behavioral, medical, and socioeconomic factors often trigger obesity incidence,” said Mary L. Rosser, director of integrated women’s health, Obstetrics and Gynecology at Columbia University’s Irving Medical Center in New York City . “Sedentary lifestyle, poor diet, stress, mental health, sleep deprivation, medical problems like hypothyroidism, PCOS [polycystic ovary syndrome], Diabetes and others contribute to it. “
For these other factors I would add genetics, medications, muscle wasting (sarcopenia), hormones, the gut microbiome, and any social determinants of health. The last category includes access to and quality of education, health care, neighborhood help, economic stability, gender, race, and more.
Pointing out unhealthy food environments as another problematic factor, Freedhoff says: “There is no event too small to be celebrated with food where highly processed foods and their advertising are omnipresent.”
Rosser also believes that weight changes in women between the ages of 20 and 60 are related to pregnancy and menopause. Weight gained during pregnancy is not always lost, and multiple pregnancies are often responsible for weight gain in middle age.
And menopause, a normal part of aging characterized by a decrease in estrogen and progesterone, can also be related to changes in body composition and fat distribution. “Changes related to fluctuations in these hormones begin in the mid to late 1940s and can last four to ten years,” said Rosser. She adds that estrogen therapy does not prevent weight gain in postmenopausal women, although it can minimize fat redistribution.
“Several studies have shown that perimenopause, regardless of age, is associated with an increased amount of fat in the abdomen and reduced lean body mass,” said Rosser. This explains the transition from a pear-shaped body with more weight below the waist to an apple-shaped body with more weight above the waist.
There are as many ways to lose weight as there are reasons why we are gaining weight in the first place. But first think about whether this excess weight is putting your health at risk. Remember, just one number on the scale is not a sufficient determinant of your overall health. Perhaps your height is just right for your age and you can learn to love her even if you are a few pounds heavier than you were when you were 30.
If your weight gain is unhealthy or bothering you for any other reason, the key to losing weight is figuring out why you put it on. You can rule out a slow metabolism, but it’s worth researching your diet, exercise patterns, sleep schedule, stress levels, hormones, and general health. Consider keeping a diet, exercise, and sleep diary to get a clear picture of your current habits, then find a sustainable plan that will work long-term (so not a fad).
While it can be frustrating to learn that you can’t blame your metabolism for the extra pounds, it also provides an opportunity to dig deeper and learn more about your weight. A doctor can help you determine if a lifestyle change is needed or if you need medical advice for a more complex weight-related problem involving a poor eating environment, hormonal issues, or unresolved past trauma affecting your eating habits.
Look for a practitioner who has no weight stigma and who practices with unbiased, intuitive eating principles in mind.
Registered Nutritionist Cara Rosenbloom is President of Words to Eat By, specializing in writing, nutrition education and recipe development. She is the co-author of “Food to Grow On”.