Outside of science or anatomy class, there are a couple ways to speak about metabolism. It usually operates in comparisons of speed and sex. Boys’ metabolisms, the thinking goes, are “fast,” therefore permitting them to eat whatever they want—much to the chagrin of girls, who have “slow” metabolisms that require them to perhaps be more “mindful” of what they eat.
In most living organisms, metabolism refers to a suite of chemical processes that enable the body to access the nutrients it needs to live. Food (carbohydrates, proteins, fats, vitamins, and minerals) goes into the body, is broken down, and duly distributed via metabolic “pathways.” These lead to the heart, liver, kidneys, and brain—organs that altogether account for 65 percent of metabolic rate in humans.
Metabolism alone, of course, does not determine weight, nor does it abide by gender roles. A recent study published in Science confirms that it is much trickier than that.
Source: Science Magazine
The research, which some scientists suggest could change the way human anatomy and physiology are taught, used data from more than 6,000 people from an age of eight months to 95 years. Through the data, the authors charted the trajectory of metabolism through the years. Oh, and sorry boys and girls: there is “no real difference” of metabolic rate between sexes.
Instead, “metabolism differs for all people across four distinct stages of life.” For about a month after babies are born, their metabolism is like that of the mother. Then, “something kicks in” until age one, when metabolism works at its peak, 50 percent above the adult rate.
From age one to 20, the rate slows down gradually at about 3 percent a year. From age 20 to 60, metabolism “holds steady,” experiencing no major changes. Then, from age 60, metabolic rate declines at just under 1 percent a year.
That 1 percent a year equals a decline of 20 percent at age 95. Such a decline in metabolic rate, the study seems to suggest, brings about the effects of old age. While the heart, liver, kidneys, and brain take up 65 percent of resting metabolic rate, the organs only make up 5 percent of body weight. A slower metabolism “may mean that crucial organs are functioning less well as people age.” Compromised organs in turn have a higher chance of suffering from chronic disease.
Those extra pounds added on after college? You may blame food intake, lifestyle, or lack of exercise –but you may not blame them on a “slower metabolism!”
Educators: how may you illustrate changes in metabolic rates on Anatomy in Clay® Learning System models?