Scientists discovered what happens when one twin exercises and the other does not


probiotic illustration twins fat skinny

Skye Gould / Business Insider

We all know that exercise is good for us. But many of us still can't seem to drag ourselves to the park or gym to break a sweat - only 20% of Americans meet the CDC's guidelines for aerobic and muscle-strengthening workouts.


Anyone who holds back because they're just not sure how much of a difference exercise can make should take a look at a new study out of Finland, where researchers came up with a way to show just how crucial exercise can be to a healthier life.

As the New York Times reports, those researchers looked at ten pairs of identical twins (so they'd be genetically the same), and chose pairs in which as adults, one twin exercised regularly and the other didn't. (Both had been active as children.) In most cases the twins had similar diets but one had stopped exercising, usually within the past three years, mostly due to family or work pressures.

The study showed that exercise was powerfully associated with changes in the body and the brain, even when the people involved were starting with the same basic genetic material.

The active twins had lower body fat and greater endurance capacity, while the less active twins showed signs of insulin resistance, which can be precursor of metabolic problems and eventually diabetes. As the Times points out, the exercisers also showed increased grey matter in their brains, especially in the parts of the brain associated with coordination and motor control - in other words, not only did a few years of exercise make a huge difference in physical fitness, it was also associated with significant brain changes.


The study was very small and not randomized, so while exercise has long been associated with better health, this particular experiment can't prove cause-and-effect. And the twins' lives as adults may have diverged in many ways beyond exercise: diet, family life, stresses, and sleep schedule, to name just a few. A small study can't possibly control for all the possible confounding factors, and the results will need to be confirmed in much larger groups.

Still, the researchers explained to the Times, doing the study with twins showed things that would be impossible to demonstrate otherwise. The fact that twins have the same genes meant the researchers could control for genetic differences, which is hard to do with fitness studies.

It also shows how just a few years of lifestyle change might actually make a difference over time, no matter what your genetic predispositions are.

That's an encouraging reason to get out and exercise.

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