Some individuals hold aging and a decline in metabolism responsible for their weight gain in middle age, and they surrender to their excess weight as if it were an inevitable fate, so the solution is to buy new clothes instead of those that have become tight, and they continue to console themselves that this is the year of life.
Is gaining weight in the middle of work really inevitable? Is slowing metabolism solely responsible for weight gain?
Amidst the avalanche of health advice and dietary fluctuations, Dr. Matthias Fehervari, a consultant obesity surgeon at Nuffield Health in the United Kingdom, with extensive experience in metabolic issues, provides an explanation about this to the British newspaper The Independent.
What is metabolism?
“Metabolism is the chemical processes that keep our bodies functioning, from converting food into energy, repairing cells and supporting organ function,” Fehervari says.
Metabolic rate expresses the amount of energy the body uses to maintain these vital processes.
“Even when you are resting, your body is still working to keep your heart beating, your lungs breathing, and your brain active, and this is what is known as the basal metabolic rate,” Fehervari adds.
Misconceptions about metabolism
A common misconception is that metabolism alone determines body weight. “Weight regulation is shaped by a complex network of factors that extend beyond burning calories,” explains Fehervari. “These factors include diet quality, muscle mass, sleep, and physical activity, as well as deeper physiological mechanisms such as changes in bile flow, modifications in stomach function and size, vagal nerve signaling, and modulation of gut hormones.”
The gut microbiome also plays a vital role, affecting how well we extract energy from food, how we process bile acids, and how our metabolism works overall.
Some people assume that metabolism declines steadily after early adulthood, but that is inaccurate. “Large-scale, high-quality studies show that it remains remarkably stable for decades before gradually slowing down later in life,” Fehervari says.
How does metabolism change with age?
Fehervari says: “The metabolism is not a straight descending curve, as an important study published in the journal Science in 2021, which included more than 6,000 people, showed that energy expenditure peaks in childhood – where it can be 50% higher than in adults – and then gradually decreases until approximately the age of twenty.”
Metabolic rate remains remarkably stable when adjusted for body size and composition from the twenties until about sixty, and after sixty the metabolic rate tends to decline slowly, but measurably.
What are the reasons for this decline from the age of sixty onwards?
“After age 60, metabolic rate typically declines by about 0.7% per year,” says Fehervari. “The main reasons are loss of muscle mass, decreased physical activity, and minor hormonal changes such as declining levels of growth hormone and sex hormones.”
The efficiency of mitochondria – the body’s energy production mechanism – may decrease slightly with age. This does not mean that the body forgets how to burn energy, but rather that it becomes less efficient at doing so.
What lifestyle factors affect metabolism?
Many lifestyle habits can support or slow metabolic function.
Low muscle mass or lethargy
“Muscle tissue burns more energy than fat, even at rest,” Fehervari explains.
Follow a strict diet
“Severe calorie restriction can temporarily suppress metabolic rate,” explains Fehervari.
Lack of sleep
“Lack of sleep may affect hunger and energy-regulating hormones such as leptin and ghrelin,” Fehervari points out.
Chronic stress
“High cortisol can promote fat storage and affect energy use,” says Fehervari.