NYT –

The researchers were looking for young adult identical twins in their early- to mid-20s whose exercise habits had substantially diverged after they had left their childhood homes. These twins were not easy to find. Most of the pairs had maintained remarkably similar exercise routines, despite living apart.

But eventually, the researchers homed in on 10 pairs of male identical twins, one of whom regularly exercised, while the other did not, usually because of work or family pressures, the researchers determined.

The dissimilarities in their exercise routines had mostly begun within the past three years, according to their questionnaires.

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.

Then they compared the twins’ results.

It turned out that these genetically identical twins looked surprisingly different beneath the skin and skull. The sedentary twins had lower endurance capacities, higher body fat percentages, and signs of insulin resistance, signalling the onset of metabolic problems. (Interestingly, the twins tended to have very similar diets, whatever their workout routines, so food choices were unlikely to have contributed to health differences.)

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.

Presumably, all of these differences in the young men’s bodies and brains had developed during their few, brief years of divergent workouts, underscoring how rapidly and robustly exercising – or not – can affect health, said Dr. Urho Kujala, a professor of sports and exercise medicine at the University of Jyvaskyla who oversaw the study.

Of course, the study was small and not a formal randomized trial, although it involved identical twins.

But Dr. Kujala said he believes that the results strongly imply that the differences in the twin’s exercise habits caused the differences in their bodies.

The above is already being panned as not being a randomized study — and that’s clearly true.

But, think about it: No researcher would ever be allowed to force the unwilling to exercise at gunpoint. And, with all we already know about health and fitness, could anyone ever get a university ethics review board to approve stopping people from exercising for a lifetime?

Critics can call this whatever they want. The fact of the matter remains, this is the best we are ever going to get — and it’s very close to definitive.

You can take two people who have identical genetics and who were raised in an identical environment with identical fitness levels who still eat pretty much the same and, with the simple addition or subtraction of exercise, change nearly everything that matters about the person’s health in about three years.

Obviously, there are stupid things you can do with your diet that can override nearly any level of exercise but, with all other elements remaining largely equal what we have always guessed to be true has just been proven:

Exercise is still, hands down, the key element of health and fitness.