Genetics, Environment, Inclination, and Destiny

Astonishing as this might seem, the debate about exercise has been going on for decades. After all the years and all the studies, and all the documented personal experience, one might think that by now, consensus would have been reached on the usefulness of exercise as a weight-loss tool. But no. Some people are firmly convinced that exercise is the only savior; others believe it makes no difference, and a very large number is still thoroughly confused.

Once in a while, fate provides the perfect opportunity for research. Thanks to life’s well-known randomness and weirdness, looking at nature’s matched sets enables scholars to make interesting conclusions of various kinds.

Curious Scandinavians

For years, Finland has been collecting statistics from identical twins and compiling them in the FinnTwin16 database. When the volunteers are 16 years old, they sign up to answer a batch of questions, then periodically fill out the questionnaires again every few years.

Heredity has a lot to do with how people’s bodies respond to exercise, and the amount of endurance capacity they have, as well as how much they enjoy sweating. Some people have never in their life experienced a “runner’s high” and have no desire to.

Scientists wanted to zero in on genetically identical pairs of males in their twenties, who had grown up with similar patterns of physical exertion. For the purpose of this study, each pair needed one twin who had exercised regularly in adulthood, and one who, hampered by work or family obligations, had not done so. These were surprisingly difficult to find. Set after set of male twins, even though living apart, adhered to remarkably similar exercise patterns.

In this case, the diet was not a major concern, which is just as well, because even among the relatively few pairs who exercised differently, food choices did not vary enough to be significant. Eventually, the scholars settled on 10 sets of twin brothers, whose exercise habits had diverged mostly within the past three years. Journalist Gretchen Reynolds explained,

The scientists invited these twins into the lab and measured each young man’s endurance capacity, body composition and insulin sensitivity, to determine their fitness and metabolic health. The scientists also scanned each twin’s brain.

The sedentary twins had lower endurance capacities, higher body fat percentages, and signs of insulin resistance, signaling the onset of metabolic problems.

The twins’ brains also were unalike. The active twins had significantly more grey matter than the sedentary twins, especially in areas of the brain involved in motor control and coordination.

At the University of Jyvaskyla, research team leader Dr. Urho Kujala noticed a common thread in each pair of twins, no matter what their genes dictated, and regardless of what their early training and habituation had entailed. In the realm of individual behavior, none of the influences is guaranteed to “take.” Apparently, it is not carved in stone that either heredity or environment can rule uncontested. Genetics and environment can both foster tendencies, but neither factor inevitably signals destiny.

Your responses and feedback are welcome!

Source: “One Twin Exercises, the Other Doesn’t,”, 03/04/15
Image by Lily Ballard/CC BY 2.0

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About Dr. Robert A. Pretlow

Dr. Robert A. Pretlow is a pediatrician and childhood obesity specialist. He has been researching and spreading awareness on the childhood obesity epidemic in the US for more than a decade.
You can contact Dr. Pretlow at:


Dr. Pretlow’s invited presentation at the American Society of Animal Science 2020 Conference
What’s Causing Obesity in Companion Animals and What Can We Do About It

Dr. Pretlow’s invited presentation at the World Obesity Federation 2019 Conference:
Food/Eating Addiction and the Displacement Mechanism

Dr. Pretlow’s Multi-Center Clinical Trial Kick-off Speech 2018:
Obesity: Tackling the Root Cause

Dr. Pretlow’s 2017 Workshop on
Treatment of Obesity Using the Addiction Model

Dr. Pretlow’s invited presentation for
TEC and UNC 2016

Dr. Pretlow’s invited presentation at the 2015 Obesity Summit in London, UK.

Dr. Pretlow’s invited keynote at the 2014 European Childhood Obesity Group Congress in Salzburg, Austria.

Dr. Pretlow’s presentation at the 2013 European Congress on Obesity in Liverpool, UK.

Dr. Pretlow’s presentation at the 2011 International Conference on Childhood Obesity in Lisbon, Portugal.

Dr. Pretlow’s presentation at the 2010 Uniting Against Childhood Obesity Conference in Houston, TX.

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